SEARCH · PubMed Health

Results for “Tachyglossidae”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources

PubMed1988

The lamina cribrosa of Ornithorhynchus (Monotremata, Mammalia).

A vestigial and transitory lamina cribrosa was found in nestling platypus (Ornithorhynchus anatinus). The heads of two nest-young (180 and 333 mm length), one subadult and one adult Ornithorhynchus were serially sectioned and studied with special reference to the development of the nasal region. In nest-young Ornithorhynchus an irregularly shaped bar of cartilage develops at the foramen olfactorium advehens. In the subadult it is largely resorbed, and in the osseous skull of the adult it is completely lacking. Ontogeny and topographical relationships of this bar of cartilage indicate that it is part of a lamina cribrosa. It embraces the ramus medialis of the nervus ethmoidalis and the arteria ethmoidalis, as do the corresponding parts of the lamina cribrosa of Tachyglossus. Compared to other parts of the chondrocranium this bar develops late in ontogeny, as does the lamina cribrosa of other mammals. Therefore, it can be concluded that part of the lamina cribrosa is present for a short period during the ontogeny of Ornithorhynchus, contrary to earlier reports. As in many other water-adapted mammals, the olfactory system of Ornithorhynchus is reduced. This suggests that the rest of the lamina cribrosa of Ornithorhynchus is secondarily reduced. The common ancestor of Ornithorhynchus and Tachyglossidae most probably possessed a lamina cribrosa which can be traced back to the common mammalian stock. The lamina cribrosa developed only once in the phylogeny of mammals. Its lack in the adult Ornithorhynchus is not a "reptilian" character.

Animals↗

PubMedDate not supplied

[Evolution of tetrapod locomotion].

Fish-like ancestors of tetrapods did not need strong limb musculature because they inhabited waters and were practically imponderable. In the primitive tetrapods, principal function of the limbs was initially restricted to passive anchoring in the course of animal movements on the substrate by means of lateral bending of the body (undulation). However, progressive development of carrying function of tetrapod limbs lead to clearing the body off the substrate which reduced friction costs and made the tetrapods less dependent on the substrate properties. Along with this, the limbs became more important as the active locomotory organs. But at the beginning, this diminished locomotory speed as the momentum caused by undulation could no longer provide additional forward sliding. Locomotory function of the tetrapod limb could be carried out due to both retraction and pronation at the shoulder joint. Relatively short humerus of the primitive tetrapods made it indifferent which of these two particular actions lead to elongation of the steps. In most of the recent tetrapods with sprawling limbs (Urodela, Lacertilia Sphenodontia, Crocodilia), step elongation was carried out mainly by retraction at the shoulder joint. Contrary to this, in Tachyglossidae (Mammalia: Monotremata) retraction is absent while pronation at the shoulder joint becomes the most important component of step elongation. This made it possible to recognize two principal types, pronatory and retractory, of locomotion on the basis of the main movement in the phase of support. A mathematical model describing changes in step length during the phase of support in both of these types is elaborated. It takes into account relative sizes of stylopodium and zeugopodium, the angles of pronation and retraction at the shoulder joint, the angle of adduction at the elbow joint, and the angle of body undulation arc. It is shown on the basis of this model, varying of which of the above parameters is advantageous and which is disadvantageous in each of the locomotory types. In the pronatory locomotory type, adduction (lateral mobility) at the elbow joint is employed. It leads to special changes in morphology of the elbow joint due to which humeral condyle becomes spherical and promotes both adduction and rotation of the entire antebrachium. In the retractory locomotory type, amplification of pronation is to be limited in order to provide step elongation, so certain morphological adaptations occur in the elbow joint which prevent adduction at this joint. For step elongation, retraction at the shoulder joint is usually more advantageous than pronation, therefore historical emergence of the pronatory type could be considered as inadaptive. However, transversal horizontal axis of rotation at the shoulder joint appeared to be a prerequisite of the subsequent appearance of the most perfect locomotion in the therian mammals with their parasagittal limbs. Transition to the parasagittal limb construction was associated with adaptation to jumping asymmetric locomotion. It caused elongation of the shoulder bone downward which lead to widening of rotation cone of the humerus and, at the same time, to reduction of the coracoid portion of the glenoid fossa, the latter became horizontal rather than lateral. As a part of this process, the longitudinal axis of the scapula was displacing caudally with destruction of the suture-like articulation of the acromion process with the clavicle. The latter became articulated with the sternum directly or via much reduced interclavicle (or via procoracoid rudiment). This increases amortisatory function of the shoulder girdle during landing at the final stage of jump.

Amphibians↗

PubMed1996

Morphology of the monotreme organ of Corti and macula lagena.

The organ of Corti and macula lagena were studied by scanning and transmission electron microscopy in two species of monotreme, the platypus and echidna. In both species, the organ of Corti had a fundamentally mammalian conformation, with distinct outer and inner hair cells, separated by a tunnel of Corti. However, unlike eutherian mammals, the monotremes had three or four rows of pillar cells, and four to five rows of inner hair cells. The organ of Corti was much shorter than in eutherian mammals, at 4.4 mm (platypus), and 7.6 mm (echidna). While the total number of outer hair cells (3,350 platypus, 5,050 echidna) was many fewer than in most eutherian mammals, the total number of inner hair cells (1,600 platypus, 2,700 echidna) was comparable with that in eutherian mammals. The stereocilia on both inner and outer hair cells underwent a systematic change in orientation across the cochlear duct, with those nearest the tunnel of Corti having their axis of symmetry oriented transversely across the duct, and those on the outer edge of the organ having the axis oriented nearly longitudinally along the duct. The macula lagena had signs of a vestibular epithelium, with tall bundles of stereocilia, a division into areas with bundles of opposing orientation and type I and type II hair cells.

Animals↗

PubMed1999

Parathyroids and ultimobranchial bodies in monotremes.

Only scant information is available in the scientific literature on the parathyroids and ultimobranchial bodies in the primitive mammals, the echidna (Tachyglossus aculeatus) and platypus (Ornithorhynchus anatinus). The major aim of this paper is to describe the morphology of the monotreme parathyroid gland and to compare it with parathyroids in mammals and reptiles. The gross anatomy and light microscopic structure of the ultimobranchial body, thymus, and thyroid are also given. Animals were dissected and routine light and electron microscopic techniques used to examine the microscopic morphology. The locations of parathyroid hormone, calcitonin and calcitonin gene-related peptide in tissue sections were identified by immunostaining. Monotremes have one pair of parathyroid glands located in the thorax and they are often associated with thymic tissue but never with the thyroid which is also present in the mediastinum. Ultimobranchial bodies are ventrolateral to the commencement of the trachea. Thymic lobules with Hassall's corpuscles are scattered in the fibrofatty tissue of the mediastinum and the ventral surface of the pericardium. Histologically, principal cells, water-clear cells, and non-secretory cells were identified in the parathyroid glands. Principal cells showed polarity and had microlamellar projections that formed intercellular canaliculi. Non-secretory cells had features similar to those of thymic epithelial reticular cells. Immunostaining of parathyroid hormone showed a diffuse distribution in parathyroid principal cells and none in ultimobranchial bodies. Identification of the ultimobranchial bodies was confirmed by immunostaining. The monotreme parathyroid gland, ultimobranchial bodies and thyroid show reptilian as well as mammalian features.

Animals↗

PubMed2000

Descriptive study of the diaphragm and lungs in the short-nosed echidna, Tachyglossus aculeatus (Mammalia: monotremata).

In this descriptive study, we characterize the diaphragm and lungs of the short-nosed echidna, Tachyglossus aculeatus, using a combination of gross anatomical, light-microscopic, electron microscopic, and morphometric techniques, including airway casting. The diaphragm is inclined from ventro-cranial to dorso-caudal and possesses a large central tendon (centrum tendineum). The crural and costal muscle groups and the associated trigoni are located in the same positions as in other mammals. The bronchial branching pattern reveals cranially broad, tapering stem bronchi and an unusually small number of first order bronchi. The asymmetrical primary branching pattern and possibly also the asymmetry of right and left lungs are plesiomorphic within the Mammalia. The histology and ultrastructure of the airways and lung parenchyma reveal no unusual features: alveolar type 1 and type 2 cells in the parenchyma; type 2 cells, exocrine bronchiolar cells (Clara cells), ciliated cells, and goblet cells in the terminal airways and the latter two cell types in the bronchi. Both a double and a single capillary net are found on the interalveolar septa. The high capillary loading of the double net may be of selective advantage because of long apneas and low metabolic rate in the echidna.

Animals↗

PubMed1979

An evolutionary view of the male reproductive tract and sperm maturation in a monotreme mammal--the echidna, Tachyglossus aculeatus.

In exploring the evolution and adaptive significance of epididymal function, we have studied the male excurrent duct and spermatozoa of a monotreme mammal--the echidna. Sperm maturation in the echidna excurrent duct appears simpler than that in most therians examined. Furthermore, neither the duct nor the spermatozoa of the echidna display specific therian characteristics; they bear a much closer resemblance to those of non-passerine birds. The echidna spermatozoon is filiform, the sperm tail has no distinctive features, and the anterior seventh of the undulating nucleus is covered by a modest acrosome. Immediately behind this a restricted apposition between plasma membrane and nuclear envelope constitutes a post-acrosomal ring. This is evident also in some reptiles and marsupials, whereas in Eutheria such a membrane association appears as the posterior ring at the base of the sperm nucleus. Maturation of spermatozoa in the Wolffian duct of the echidna appears to be expressed only in a changing capacity for motility and in loss of the cytoplasmic droplet. Neither surface, structural nor acrosomal changes that characterize sperm maturation in therian mammals have been detected in maturing echidna spermatozoa. The echidna duct displays little of the regional complexity of the epithelium that typifies this duct in the Theria. Of five regions distinguishable on the basis of epithelial morphology, the first two appear to be counterparts of efferent ducts by virtue of a low columnar, partially ciliated epithelium. The tall pseudo-stratified Golgi-rich epithelium of the major portion of the duct broadly resembles that of the therian epididymis, but it displays only two structurally distinguishable regions, the more distal being the site of a dense luminal secretion. The foamy epithelial cells of the fifth and terminal region, characterized by a mass of supra-nuclear vesicles and rough ER, suggest a secretory function that may in some way contribute significantly to the ejaculate, for accessory glands are poorly developed in monotremes. The possibility is considered that the relative complexity of epididymal function and sperm structure in therian mammals could have been determined by evolutionary change in the milieu of the female tract, and/or in the character of the egg vestments that the fertilizing spermatozoon must penetrate.

Animals↗

PubMed1991

Cartilaginous bone extremities of growing monotremes appear unique.

Cartilage canals are present in the epiphyseal cartilage of most mammals and birds. They are considered necessary for the maintenance of chondrocytes and for the formation of epiphyseal ossification centers. The epiphyseal cartilage of marsupials was recently shown not to contain cartilage canals, and placental rats appear not to have cartilage canals, although some confusion exists in the literature. The present study examines the cartilaginous epiphyses and physes from the knee and hip of the rat and the two Australian monotremes (platypus, Ornithorhynchus anatinus and echidna, Tachyglossus aculeatus). In all three species, cartilage canals were absent. Vessels to epiphyseal ossification centers were present, however. In the center of the cartilaginous femoral head of the echidna, but not in the platypus or rat, there was a large cavity, which contained connective tissue and was lined by an endochondrium of chondroproginator cells. These appeared to be contributing to growth of the cartilaginous epiphysis. No similar structure has previously been described in the cartilaginous epiphysis of other species. There was no ligament of the femoral head in the hip joints of the monotremes, and it is suggested the absence of a ligament may be significant in the development of the cavity. It was noted in all specimens that despite being avascular the epiphyseal and physeal cartilage appeared viable and functionally normal. The small size of the cartilaginous epiphyses of the rat may account for their avascularity; but the epiphyses of the monotremes were much larger, especially the echidna, yet still avascular. These features provide strong evidence for fundamental differences between the avascular cartilage of monotremes and the vascular cartilage of most mammals.

Animals↗

PubMed2005

Distribution of caspase-14 in epidermis and hair follicles is evolutionarily conserved among mammals.

Caspase-14, a member of the caspase family of cysteine proteases, is almost exclusively expressed in the epidermis. Studies on human and mouse cells and tissues have implicated caspase-14 in terminal differentiation of epidermal keratinocytes and in the formation of the stratum corneum. Here we investigated evolutionary aspects of the role of caspase-14 by analyzing its distribution in the epidermis and hair follicles of representative species of placental mammals, marsupials, and monotremes. Immunocytochemical staining showed that caspase-14 is consistently expressed in the granular and corneous layer of the epidermis of all mammalian species investigated. Ultrastructural analysis using gold-labeled anticaspase-14 antibodies revealed that caspase-14 is associated preferentially with keratin bundles and amorphous material of keratohyalin granules, but is also present in nuclei of transitional cells of the granular layer and in corneocytes. In hair follicles, caspase-14 was diffusely present in cornifying cells of the outer root sheath, in the companion layer, and, most abundantly, in the inner root sheath of all mammalian species here analyzed. In Henle and Huxley layers of the inner root sheath, labeling was seen in nuclei and, more diffusely, among trichohyalin granules of cornifying cells. In summary, the tissue expression pattern and the intracellular localization of caspase-14 are highly conserved among diverse mammalian species, suggesting that this enzyme is involved in a molecular process that appeared early in the evolution of mammalian skin. The association of caspase-14 with keratohyalin and trichohyalin granules may indicate a specific role of caspase-14 in the maturation of these keratinocyte-specific structures.

Animals↗

PubMed2003

Tactile sensory function in the forearm of the monotreme Tachyglossus aculeatus.

Peripheral tactile neural mechanisms in the forepaw of the echidna (Tachyglossus aculeatus, from the order Monotremata) were investigated to establish the extent of correspondence or divergence that has emerged over the widely different evolutionary paths taken by monotreme and placental mammals. Electrophysiological recordings were made in anesthetized echidnas from 29 single tactile sensory nerve fibers isolated in fine strands of the median or ulnar nerves of the forearm. Controlled tactile stimuli were applied to the forepaw glabrous skin to classify fibers, initially, into two broad divisions, according to their responses to static skin displacement. One displayed slowly adapting (SA) response properties, and the other showed a selective sensitivity to the dynamic components of the skin displacement. The SA class was made up of low-threshold SA fibers and other less sensitive SA fibers, and the purely dynamically sensitive tactile fibers could be subdivided according to vibrotactile sensitivity and receptive field characteristics into a rapidly adapting (RA) class, sensitive to low-frequency (< or =50-Hz) vibration, that resembled a corresponding RA class in placental species, and another class, sensitive to a broader range of vibrotactile frequencies (approximately 50-300 Hz), that may represent a monotreme equivalent of the Pacinian corpuscle (PC)-related fiber class of placental mammals. The differential tactile sensitivity of the three principal fiber classes and their individual coding characteristics, determined by quantitative stimulus-response analysis, indicate, first, that this triad of fiber classes can subserve high-acuity tactile signalling from the echidna footpad and, second, that peripheral tactile sensory mechanisms are highly conserved across evolutionarily divergent mammalian orders.

Afferent Pathways↗

PubMed2004

Cyto- and chemoarchitecture of the cerebral cortex of the Australian echidna (Tachyglossus aculeatus). I. Areal organization.

We have examined the topography of the cerebral cortex of the Australian echidna (Tachyglossus aculeatus), using Nissl and myelin staining, immunoreactivity for parvalbumin, calbindin, and nonphosphorylated neurofilament protein (SMI-32 antibody), and histochemistry for acetylcholinesterase (AChE) and NADPH diaphorase. Myelinated fibers terminating in layer IV of the cortex were abundant in the primary sensory cortical areas (areas S1, R, and PV of somatosensory cortex; primary visual cortex) as well as the frontal cortex. Parvalbumin immunoreactivity was particularly intense in the neuropil and somata of somatosensory regions (S1, R, and PV areas) but was poor in motor cortex. Immunoreactivity with the SMI-32 antibody was largely confined to a single sublayer of layer V pyramidal neurons in discrete subregions of the somatosensory, visual, and auditory cortices, as well as a large field in the frontal cortex (Fr1). Surprisingly, SMI-32 neurons were absent from the motor cortex. In AChE preparations, S1, R, V1, and A regions displayed intense reactivity in supragranular layers. Our findings indicate that there is substantial regional differentiation in the expanded frontal cortex of this monotreme. Although we agree with many of the boundaries identified by previous authors in this unusual mammal (Abbie [1940] J. Comp. Neurol. 72:429-467), we present an updated nomenclature for cortical areas that more accurately reflects findings from functional and chemoarchitectural studies.

Acetylcholinesterase↗

PubMed2005

Cyto- and chemoarchitecture of the cerebral cortex of an echidna (Tachyglossus aculeatus). II. Laminar organization and synaptic density.

We have examined the distribution and morphology of neurons immunoreactive for nonphosphorylated neurofilament protein (SMI-32 antibody), calcium-binding proteins (parvalbumin, calbindin, calretinin), and neuropeptide Y as well as neurons reactive for NADPH diaphorase in the cerebral cortex of the Australian short-beaked echidna (Tachyglossus aculeatus). We have also studied synaptic morphology and density in S1 somatosensory cortex and assessed parameters associated with metabolic activity of the cerebral cortex (vessel volume density, mitochondrial volume density, and mitochondrial numerical density) in semi- and ultrathin sections. SMI-32 immunoreactivity was found mostly in layer V pyramidal neurons in selected cortical regions (S1, PV, V1, A). These neurons often showed atypical morphology compared with therian cortex. Neurons immunoreactive for calcium-binding proteins were broadly similar in both morphology and distribution to those seen in therian cortex, although calretinin-immunoreactive neurons were rare. Both Gray type I and Gray type II synapses could be identified in echidna S1 cortex and were similar to those seen in therian cortex. Peak synaptic density was in upper layer IV, followed by layer I, lower layer II, and upper layer III. Most synapses were of type I (72%), although types I and II were encountered with similar frequency in lower layer II and upper layer III. The capillary volume fraction values obtained for the echidna (from 1.18% in V1 to 1.34% in S1 cortex) fall within the values for rodent cortex. Similarly, values for mitochondrial volume fraction in echidna somatosensory cortex (4.68% +/- 1.76%) were comparable to those in eutherian cortex.

Animals↗

PubMed1984

Thalamic projections to the somatosensory cortex of the echidna, Tachyglossus aculeatus.

Evoked potential studies (Lende, '64) suggest that echidnas have a single, topographically organized somatosensory area (SMI) that spans a mediolaterally oriented sulcus called sulcus alpha. A motor area (MI) is situated on the prealpha gyrus. This study examines the cytoarchitecture and thalamic afferents of SMI in the echidna, Tachyglossus aculeatus. SMI contains two cytoarchitectonic fields. A caudal field extends across the postalpha gyrus and onto the floor of sulcus alpha. It has a well-developed layer 4 and a relatively small number of medium-sized pyramidal cells in layer 5. The rostral field extends from the floor of sulcus alpha onto its rostral bank. It also has a well-developed layer 4 but has a large number of large pyramidal cells in layer 5. Layer 4 thins as it is followed onto the crown of the prealpha gyrus. The remainder of this gyrus contains a single cytoarchitectonic field with a thin layer 4 and a layer 5 heavily populated with larger pyramidal cells. This field corresponds to the physiologically defined motor area MI. Thalamic afferents to SMI were examined by placing pressure injections of horseradish peroxidase into the two cytoarchitectonic fields. An injection that involved both fields retrogradely labeled neurons throughout the ventral posterior nucleus of the thalamus. An injection restricted to the caudal field labeled a band of neurons that extends rostrocaudally throughout the ventral part of the ventral posterior nucleus. An injection restricted to the rostral field labeled a band of neurons situated dorsally in the ventral posterior nucleus. No other thalamic groups contained labeled neurons comparable to the labeling seen in the intralaminar or posterior nuclei following a horseradish peroxidase injection into SI of marsupial or placental mammals. These results indicate that SMI in Tachyglossus contains two cytoarchitectonic fields that resemble areas 3a and 3b in some placental mammals, suggesting that the constellation of cytoarchitectonic fields corresponding to areas 4, 3a, and 3b is a basic mammalian character which has been modified in marsupial and many placental mammals.

Afferent Pathways↗

PubMed1992

Müller cells in vascular and avascular retinae: a survey of seven mammals.

Eight monoclonal antibodies were used to label Müller cells in four mammals that have vascular retinae (cats, dogs, humans, and rats) and in three with avascular retinae (echidnas, guinea pigs, and rabbits). Müller cells were found to have a fairly uniform retinal distribution in seven species, with a mean density of 8,000-13,000 cells mm-2. Müller cells in avascular retinae differ from their vascular counterparts in four respects. First, they are shorter than those in vascular retinae. This difference is mainly due to a reduction in the thickness of the outer nuclear layer. Second, the trunks of Müller cells in avascular retinae tend to be thicker, although those in echidnas are an exception to this trend. Third, Müller cell rootlets in avascular retinae follow a more tortuous course than those in vascular retinae, reflecting the fact that photoreceptor nuclei in the two types of retina have different shapes and stacking patterns. Fourth, due to a reduction in the density of photoreceptors in avascular retinae, there are fewer neurones per Müller cell. Although these four features may enable Müller cells to assist the nutrition of neurones in the inner layers of avascular retinae, they are unlikely to be morphological specializations that have evolved for that purpose. Rather, these features appear to be a direct consequence of the fact that avascular retinae are thinner and have a differently organised outer nuclear layer. These features aside, Müller cells in avascular retinae closely resemble their counterparts in vascular retinae.

Animals↗

PubMed1993

Innervation of the monotreme gastrointestinal tract: a study of peptide and catecholamine distribution.

The distribution of neurons and endocrine cells containing various peptides or catecholamines was examined in the digestive tracts of the echidna (Tachyglossus aculeatus) and the platypus (Ornithorhynchus anatinus). Comparisons were made with published studies in other species in order to obtain a broader view of the phylogenetic distribution and possible functions of gut peptides and catecholamines. Further comparisons between the echidna and platypus were made in light of their different dietary features and gut histology. The distribution of neurons and axons containing catecholamines or various peptides resembled that in other species (such as the frequent appearance of axons containing substance P and vasoactive intestinal peptide in the intestinal mucosa, and axons containing substance P or enkephalins in the circular muscle). In both species, the stomach histologically resembles the esophagus, being aglandular and lined with stratified squamous epithelium. Innervation of these two organs was similar but not identical, with a greater array of peptides found in the gastric muscle. The intestinal mucosa was densely innervated in both species. The platypus small intestine is unusual in having a thick and deeply folded mucosa (but no villi), in which the superficial epithelium is absent or incomplete at many sites; many axons travel close to these luminal surfaces. Many (putative noradrenergic) axons associated with blood vessels contained neuro-peptide Y, but there was no evidence for intrinsic catecholamine-containing neurons. Somatostatin and cholecystokinin were present in some endocrine cells, but unlike many mammals, absent in neuronal tissue. These studies have shown that there are many strong similarities between monotremes and other mammals in the distribution and array of peptides found within nervous and endocrine tissues of the digestive tract. However, numerous small differences of the echidna and platypus innervation may be correlated with their different digestive structures.

Animals↗

PubMed1995

Organization of somatosensory cortex in monotremes: in search of the prototypical plan.

The present investigation was designed to determine the number and internal organization of somatosensory fields in monotremes. Microelectrode mapping methods were used in conjunction with cytochrome oxidase and myelin staining to reveal subdivisions and topography of somatosensory cortex in the platypus and the short-billed echidna. The neocortices of both monotremes were found to contain four representations of the body surface. A large area that contained neurons predominantly responsive to cutaneous stimulation of the contralateral body surface was identified as the primary somatosensory area (SI). Although the overall organization of SI was similar in both mammals, the platypus had a relatively larger representation of the bill. Furthermore, some of the neurons in the bill representation of SI were also responsive to low amplitude electrical stimulation. These neurons were spatially segregated from neurons responsive to pure mechanosensory stimulation. Another somatosensory field (R) was identified immediately rostral to SI. The topographic organization of R was similar to that found in SI; however, neurons in R responded most often to light pressure and taps to peripheral body parts. Neurons in cortex rostral to R were responsive to manipulation of joints and hard taps to the body. We termed this field the manipulation field (M). The mediolateral sequence of representation in M was similar to that of both SI and R, but was topographically less precise. Another somatosensory field, caudal to SI, was adjacent to SI laterally at the representation of the face, but medially was separated from SI by auditory cortex. Its position relative to SI and auditory cortex, and its topographic organization led us to hypothesize that this caudal field may be homologous to the parietal ventral area (PV) as described in other mammals. The evidence for the existence of four separate representations in somatosensory cortex in the two species of monotremes indicates that cortical organization is more complex in these mammals than was previously thought. Because the two monotreme families have been separate for at least 55 million years (Richardson, B.J. [1987] Aust. Mammal. 11:71-73), the present results suggest either that the original differentiation of fields occurred very early in mammalian evolution or that the potential for differentiation of somatosensory cortex into multiple fields is highly constrained in evolution, so that both species arrived at the same solution independently.

Animals↗

PubMed2005

High variability in complementarity-determining regions compensates for a low number of V gene families in the lambda light chain locus of the platypus.

Based on the analysis of a panel of variable (V) region sequences from the Australian duck-billed platypus and the Australian short beaked echidna, the monotremes were found to express a highly diversified Vlambda repertoire. High variability was observed both in sequence and in length of all three CDR regions. However, all monotreme sequences were found to form a separate branch on a distance tree, and the monotremes appear to express only two Vlambda gene families. The appearance of all Vlambda gene segments in one branch on the distance tree gives further support for the notion that deletions of entire V region clans or families, followed by successive rounds of gene duplications may be a relatively common phenomenon during vertebrate evolution. Four different constant region sequences were also identified and a preferential use of certain J segments to each constant region was observed. A more detailed picture of the locus was obtained by analysis of genomic DNA by Southern blot and PCR. The organization of the lambda locus involves multiple V and several constant region genes with one or several joining segments positioned upstream of each constant region, similar to the organization in mouse and man. An mRNA frequency analysis shows that the lambda light chain accounts for more than 90% of the light chain transcripts in the spleen. The abundance and the high variability indicate that light chain diversity at the lambda locus contributes significantly to the antigen-binding repertoire in monotremes. A high lambda to kappa light chain ratio also indicates that variability in the CDR regions is more important for the repertoire size than the total number of V gene families.

Amino Acid Sequence↗

PubMed2001

Monotreme IGF2 expression and ancestral origin of genomic imprinting.

IGF2 (insulin-like growth factor 2) and M6P/IGF2R (mannose 6-phosphate/insulin-like growth factor 2 receptor) are imprinted in marsupials and eutherians but not in birds. These results along with the absence of M6P/IGF2R imprinting in the egg-laying monotremes indicate that the parental imprinting of fetal growth-regulatory genes may be unique to viviparous mammals. In this investigation, we have cloned IGF2 from two monotreme mammals, the platypus and echidna, to further investigate the origin of imprinting. We report herein that like M6P/IGF2R, IGF2 is not imprinted in monotremes. Thus, although IGF2 encodes for a highly conserved growth factor in chordates, it is only imprinted in therian mammals. These findings support a concurrent origin of IGF2 and M6P/IGF2R imprinting in the late Jurassic/early Cretaceous period. The absence of imprinting in monotremes, despite apparent interparental conflicts over maternal-offspring exchange, argues that a fortuitous congruency of genetic and epigenetic events may have limited the phylogenetic breadth of genomic imprinting to therian mammals. J. Exp. Zool. (Mol. Dev. Evol.) 291:205-212, 2001.

Amino Acid Sequence↗

PubMed1998

Calcium-binding and structural stability of echidna and canine milk lysozymes.

For echidna and canine milk lysozymes, which were presumed to be the calcium-binding lysozymes by their amino acid sequences, we have quantitated their calcium-binding strength and examined their guanidine unfolding profiles. The calcium-binding constants of echidna and canine lysozymes were determined to be 8.6 x 10(6) M(-1) and 8.9 x 10(6) M(-1) in 0.1 M KCl at pH 7.1 and 20 C, respectively. The unfolding of decalcified canine lysozyme proceeds in the same manner as that of alpha-lactalbumin, through a stable molten globule intermediate. However, neither calcium-bound nor decalcified echidna lysozyme shows a stable molten globule intermediate. This unfolding profile of echidna lysozyme is identical to that of conventional lysozymes and pigeon egg-white lysozyme, avian calcium-binding lysozyme. This result supports the suggestion of Prager and Jolles (Prager EM, Jolles P. 1996. Animal lysozymes c and g: An overview. In: Jolles P, ed. Lysozymes: Model enzymes in biochemistry and biology. Basel-Boston-Berlin: Birkhauzer Verlag. pp 9-31) that the lineage of avian and echidna calcium-binding lysozymes and that of eutherian calcium-binding lysozymes diverged separately from that of conventional lysozymes.

Animals↗