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At least 19 recordsLinked to original sources

PubMed2005

Possible differences in pathogenicity between cane toad-, frog- and platypus-derived isolates of Mucor amphibiorum, and a platypus-derived isolate of Mucor circinelloides.

Platypuses (Ornithorhynchus anatinus) in the north of the island state of Tasmania, Australia, suffer from a serious disease called ulcerative mycosis, which is responsible for high morbidity and, presumably, mortality rates in areas where it occurs. The disease is caused by the dimorphic fungus Mucor amphibiorum, which is also found in Queensland, New South Wales and Victoria. However, it does not cause disease in platypuses in those states. It has been previously reported that a closely related fungus, Mucor circinelloides, may also be capable of causing this disease. This paper describes pathogenicity trials involving cane toads (Bufo marinus) as the experimental model. The toads were infected with either Tasmanian, platypus-derived M. amphibiorum, West Australian, frog-derived M. amphibiorum, Queensland cane-toad-derived M. amphibiorum or Tasmanian platypus-derived M. circinelloides. The Tasmanian isolates of M. amphibiorum were more likely to cause a serious, long-term infection than were Queensland or West Australian isolates, and (+) mating types caused a more serious infection than the (-) mating type. The isolate of M. circinelloides was incapable of infecting the toads, lending further weight to the theory that it represents an environmental contaminant. The results suggest that an endemic strain of M. amphibiorum has mutated and become pathogenic to platypuses. Alternatively, a pathogenic strain of M. amphibiorum may have been introduced into Tasmania, where it is infecting a naïve population.

Animals↗

PubMed1998

Early development and embryology of the platypus.

Information on the pre-hatching development of the platypus, Ornithorhynchus anatinus, is reliant on a small number of specimens, whose precise age is unknown. Material collected for J. P. Hill and now housed in the Hubrecht International Embryological Laboratory, Utrecht, contributes a major source of specimens. This paper presents new observations on developmental stages from the Hill collection, which allow for a more complete description of pre-hatching development. A feature of the pre-embryonic development of the platypus is the incomplete meroblastic cleavage. A column of fine yolk spheres extends from beneath the embryonic blastodisc towards the centre of a yolky vitellus, as seen in birds. The major expansion of extra-embryonic membranes occurs after the formation of the primitive streak. The primitive streak develops within an embryonal area as part of the superficial wall of the yolk-sac, a feature also shared with marsupials, birds and reptiles. The full-term, subspheroidal, intrauterine egg of the platypus has a major axis of about 17 mm and contains a flat, 19-20 somite, neurula-stage embryo which has prominent trigeminal ganglion primordia. The embryo at this stage is in a period of rapid modelling of the major early organ primordia of the nervous system, cardiovascular system, excretory system, and somite-derived components of the body wall. Soon after laying, five primary brain vesicles are present, the trigeminal ganglia CN5 as well as CN7, CN8, CN9, CN10, CN11 and CN12 are well developed. The alimentary system has an expanded stomach, pancreatic primordia and a gall bladder. Mesonephric tubules are associated with patent mesonephric ducts, which empty laterally into the cloaca. Extra-embryonic membranes at this stage show an extensive chorioamniotic connection that extends through the greater part of the caudal half of fused amniotic folds. The vascularized yolk-sac consists of a superficial yolk-sac omphalopleura and a deep yolk-sac splanchnopleure. The non-vascularized yolk-sac comprises one-quarter of the ahembryonal pole. Some distinctive monotreme features have developed by the mid-incubation period. The head is bent at an acute angle to the main body axis. The blunt upturned snout marks the site of the future oscaruncle and on the maxilla there is a median primordial papilla representing the egg tooth. The eye is open with a partly pigmented retinal ring. The forelimbs have partly separated digits, and the hindfeet are paddles. Just before hatching the upturned snout contains an oscaruncle and a sharp recurved median egg tooth. Forelimbs are pronated with separate digits possessing claw primordia. Portions of the highly vascularized extra-embryonic membranes are attached to the umbilical region and the flattened vesicular allantois has a distal region fused with the chorion. Prominent features of the hatchling are the presence of a bluntly conical oscaruncle and a translucent, horn-like egg tooth. These structures are though to enable the hatchling to extricate itself from the egg shell. At hatching, the forelimbs exhibit clawed digits and are capable of digitopalmar prehension. Hindlimbs are still paddles with digital rays. A prominent yolk-sac navel is present. The newly hatched platypus has an external form similar to that of a new-born marsupial. The early development of the platypus has many major differences to the developmental sequence for humans, which has been categorized by the use of Carnegie Stages. The rate of somitogenesis of the platypus is faster in relation to the central nervous system morphogenesis than seen in humans, and the size of the early platypus embryonal area is massive in relation to that of humans. The unique morphology and function of extra-embryonic membranes in the platypus defies comparative staging with human development. Structures adapted for altricial survival of the platypus hatchling require the acquisition of functional competence at an earlier stage of organogenesis than seen in eutherians, although they are reminiscent of those found in new-born marsupials.

Allantois↗

PubMed2006

DMRT gene cluster analysis in the platypus: new insights into genomic organization and regulatory regions.

We isolated and characterized a cluster of platypus DMRT genes and compared their arrangement, location, and sequence across vertebrates. The DMRT gene cluster on human 9p24.3 harbors, in order, DMRT1, DMRT3, and DMRT2, which share a DM domain. DMRT1 is highly conserved and involved in sexual development in vertebrates, and deletions in this region cause sex reversal in humans. Sequence comparisons of DMRT genes between species have been valuable in identifying exons, control regions, and conserved nongenic regions (CNGs). The addition of platypus sequences is expected to be particularly valuable, since monotremes fill a gap in the vertebrate genome coverage. We therefore isolated and fully sequenced platypus BAC clones containing DMRT3 and DMRT2 as well as DMRT1 and then generated multispecies alignments and ran prediction programs followed by experimental verification to annotate this gene cluster. We found that the three genes have 58-66% identity to their human orthologues, lie in the same order as in other vertebrates, and colocate on 1 of the 10 platypus sex chromosomes, X5. We also predict that optimal annotation of the newly sequenced platypus genome will be challenging. The analysis of platypus sequence revealed differences in structure and sequence of the DMRT gene cluster. Multispecies comparison was particularly effective for detecting CNGs, revealing several novel potential regulatory regions within DMRT3 and DMRT2 as well as DMRT1. RT-PCR indicated that platypus DMRT1 and DMRT3 are expressed specifically in the adult testis (and not ovary), but DMRT2 has a wider expression profile, as it does for other mammals. The platypus DMRT1 expression pattern, and its location on an X chromosome, suggests an involvement in monotreme sexual development.

Amino Acid Sequence↗

PubMed1999

Haematological, serum biochemical and serological features of platypuses with and without mycotic granulomatous dermatitis.

OBJECTIVE: To determine whether there are haematological, serum biochemical and serological differences between platypuses (Ornithorhynchus anatinus) with and without granulomatous dermatitis due to Mucor amphibiorum infection. An additional objective was to establish reference haematological and serum biochemical ranges for the species in Tasmania. DESIGN: A clinicopathological and serological study. ANIMALS: A total of 37 free-living adult platypuses captured from streams and dams in Northern Tasmania were used in the clinicopathological study. Twenty-seven were clinically normal and 10 had mycotic granulomatous dermatitis. A total of 22 platypuses (20 adult and 2 juvenile) were used for the serosurvey. Eighteen were captured from streams in Northern Tasmania, and four were submitted for necropsy. RESULTS: Platypuses with mycotic ulcerative dermatitis had significantly smaller packed red cell volumes, haemoglobin concentrations, lymphocyte counts, serum cholesterol and calcium concentrations, and higher serum globulin and potassium concentrations than clinically normal animals. The lymphopenia and hyperkalaemia were thought to be clinically significant. Numbers of Trypanosoma binneyi in blood smears were similar between the two groups. Diseased platypuses had higher concentrations of serum antibody against Mucor amphibiorum as determined by ELISA compared to clinically normal platypuses. CONCLUSION: Platypuses affected by mycotic granulomatous dermatitis showed haematological and serum biochemical changes when compared to clinically normal animals from the same Tasmanian sites. A serological survey may be a useful method for detecting the prevalence of exposure to Mucor amphibiorum and humoral immunity in platypus populations both in Tasmania and the mainland of Australia.

Animals↗

PubMed2001

Energetics of foraging and locomotion in the platypus Ornithorhynchus anatinus.

We measured the energy requirements of platypuses foraging, diving and resting in a swim tank using flow-through respirometry. Also, walking metabolic rates were obtained from platypuses walking on a conventional treadmill. Energy requirements while foraging were found to depend on water temperature, body weight and dive duration and averaged 8.48 W kg(-1). Rates for subsurface swimming averaged 6.71 W kg(-1). Minimal cost of transport for subsurface swimming platypuses was 1.85 J N(-1)m(-1) at a speed of 0.4 m s(-1). Aerobic dive limit of the platypus amounted to 59 s. Metabolic rate of platypuses resting on the water surface was minimal with 3.91 W kg(-1) while minimal RMR on land was 2.08 W kg(-1). The metabolic rate for walking was 8.80 W kg(-1) and 10.56 W kg(-1) at speeds of 0.2 m s(-1) and 0.3 m s(-1), respectively. A formula was derived, which allows prediction of power requirements of platypuses in the wild from measurements of body weight, dive duration and water temperature. Platypuses were found to expend energy at only half the rate of semiaquatic eutherians of comparable body sizes during both walking and diving. However, costs of transport at optimal speed were in line with findings for eutherians. These patterns suggest that underwater locomotion of semiaquatic mammals have converged on very similar efficiencies despite differences in phylogeny and locomotor mode.

Animals↗

PubMed1998

Some related aspects of platypus electroreception: temporal integration behaviour, electroreceptive thresholds and directionality of the bill acting as an antenna.

This paper focuses on how the electric field from the prey of the platypus is detected with respect to the questions of threshold determination and how the platypus might localize its prey. A new behaviour in response to electrical stimuli below the thresholds previously reported is presented. The platypus shows a voluntary exploratory behaviour that results from a temporal integration of a number of consecutive stimulus pulses. A theoretical analysis is given, which includes the threshold dependence on the number of receptors and temporal integration of consecutive stimuli pulses, the close relationships between electrical field decay across the bill, electroreceptive thresholds and directionality of the platypus bill acting as an antenna. It is shown that a lobe shape, similar to that which has been measured, can be obtained by combining responses in a specific way from receptors sensing the electric field decay across the bill. Two possible methods for such combinations are discussed and analysed with respect to measurements and observed behaviour of the platypus. A number of factors are described which need to be considered when electroreceptive thresholds are to be determined. It is shown that some information about the distance to the source is theoretically available from the pattern of field decay across the platypus's bill. The paper includes a comparative analysis of radar target tracking and platypus prey localization.

Animals↗

PubMed1991

The survival of platypuses in captivity.

Data are presented on the duration of survival of 228 platypuses at six Australian zoos between 1934 and 1988. Only 22.4% of all platypuses survived more than 1 year in captivity. Of 15 living platypuses, 3 had been held in captivity for less than 1 year, 5 for between 1 and 5 years, 6 for between 5 and 10 years and 1 for 21 years. Of 213 platypuses that died in captivity, 81.7% had died within 1 year; most within the first month. The duration of survival was unrelated to the age of animals at acquisition or to sex. The survival rate of animals donated to zoos, including "refugees", was similar to that of purpose-caught animals. Clearly, only a small proportion of platypuses adapted to captive husbandry. The cause of death of most platypuses was not established. However, infectious disease did not appear to be significant. Approximately 28% of deaths were related to inadequate husbandry. Recommendations are made to improve the survival of platypuses in captivity. Research has commenced in zoos to facilitate this goal.

Animal Husbandry↗

PubMed1998

A sedimentation equilibrium study of platypus insulin: the HB10D mutant does not associate beyond dimer.

An extensive study of the self-association patterns of zinc-free synthetic native and mutant (HB10D) platypus insulin in solution (pH = 7.0; I = 0.1 M; 25 degrees C) has been undertaken using the method of sedimentation equilibrium. The data was fitted to a mathematical equation describing the indefinite duoisodesmic (IDI) model of self-association [A.E. Mark, P.D. Jeffrey, Biol. Chem. Hoppe-Slayer, 371 (1990) 1165]. From this the relevant association constants, KA and KB, describing the polymerising system were calculated. This information allows the calculation of the complex distribution of odd and even numbered polymeric species within the insulin system in solution. In the studies on the self-association of the synthetic native and mutant platypus insulin, each was compared with bovine insulin as well as with each other. It is concluded that there is some reduction in the extent of the self-association of native platypus insulin compared to bovine insulin. A reduction, in specifically the dimer-dimer interaction, is indicated by the higher KA and lower KB values. HB10D platypus insulin shows a dramatic reduction in self-association compared to native platypus and to bovine insulin. Analysis of the self-association pattern yielding a KB value of effectively zero suggests that the substitution of an aspartic acid residue for a histidine at B10 virtually abolishes its dimer-dimer interaction. Platypus insulin has essentially the same biological activity as that of porcine (submitted for publication) but a somewhat lower self-association, while the introduction of one amino acid in a critical region increases the activity twofold while abolishing self-association beyond dimer.

Animals↗

PubMed1999

Histological and immunohistological investigation of lymphoid tissue in the platypus (Ornithorhynchus anatinus).

The gross and histological appearance and the distribution of T and B lymphocytes and plasma cells are described for lymphoid tissues obtained from 15 platypuses. The spleen was bilobed and surrounded by a thick capsule of collagen, elastic fibres and little smooth muscle. White pulp was prominent and included germinal centres and periarterial lymphoid sheaths. Red pulp contained haematopoietic tissue. A thin lobulated thymus was located within the mediastinum overlying the heart. The cortex of lobules consisted of dense aggregates of small and medium lymphocytes, scattered macrophages and few reticular epithelial cells. In the medulla, Hassall's corpuscles were numerous, lymphocytes were small and less abundant, and reticular cells were more abundant than in the cortex. Lymphoid nodules scattered throughout loose connective tissue in cervical, pharyngeal, thoracic, mesenteric and pelvic sites measured 790 +/- 370 microm (mean +/- S.D., n = 39) in diameter, the larger of which could be observed macroscopically. These consisted of single primary or secondary follicles supported by a framework of reticular fibres. Macrophages were common in the germinal centres. The platypus had a full range of gut-associated lymphoid tissue. No tonsils were observed macroscopically but histologically they consisted of submucosal follicles and intraepithelial lymphocytes. Peyer's patches were not observed macroscopically but histologically they consisted of several prominent submucosal secondary follicles in the antimesenteric wall of the intestine. Caecal lymphoid tissue consisted of numerous secondary follicles in the submucosa and densely packed lymphocytes in the lamina propria. Bronchus-associated lymphoid tissue was not observed macroscopically but was identified in 7 of 11 platypus lungs assessed histologically. Lymphoid cells were present as primary follicles associated with bronchi, as aggregates adjacent to blood vessels and as intraepithelial lymphocytes. The distribution of T lymphocytes, identified with antihuman CD3 and CD5, and B lymphocytes and plasma cells, identified with antihuman CD79a and CD79b and antiplatypus immunoglobulin, within lymphoid tissues in the platypus was similar to that described in therian mammals except for an apparent relative paucity of B lymphocytes. This study establishes that the platypus has a well-developed lymphoid system which is comparable in histological structure to that in therian mammals. It also confirms the distinctiveness of its peripheral lymphoid tissue, namely lymphoid nodules. Platypus lymphoid tissue has all the essential cell types, namely T and B lymphocytes and plasma cells, to mount an effective immune response against foreign antigens.

Animals↗

PubMed1998

The development of the electroreceptors of the platypus (Ornithorhynchus anatinus).

A series of developmental stages of the platypus were examined to obtain an anatomical description of the development of the periphery of the electroreceptive system. Putative electroreceptors, composed of modified mucous glands, were observed to appear at 10 days post hatching (p.h.). The typical striped arrangement of peripheral electroreceptors in the platypus was seen at 12 days p.h. The arrangement of the stripes was modified during development with a range of additions and divisions of stripes occurring until the adult pattern is obtained, approximately 6 months p.h. After appearing at 10 days p.h., the number of electroreceptors increases rapidly until sometime between 24 and 28 days p.h. when there is massive death of electroreceptors, the number present at 28 days p.h. being 60% of the number present at 24 days p.h. This massive death of receptors is coincident with the appearance of other sensory structures in the epidermis of the bill skin, the push-rod mechanoreceptors and the sensory serous glands. Histological examination of a range of developmental stages demonstrated poorly differentiated innervation at 28 days p.h., which became differentiated and reached the adult configuration between 11 weeks p.h. and 6 months p.h., the time at which nestling platypuses leave the burrow. Lamination of the cells lining the duct of the electroreceptors showed a similar developmental profile. This study indicates that the electroreceptive system of the developing platypus is not functional, in a similar manner to the adult, until it is time for the platypus to leave the nesting burrow. However, the system may be functional in the developing platypus, and may be used speculatively in the location of the mammary region for suckling.

Animals↗

PubMed1993

The survival of platypus in captivity: a reappraisal with recommendations for veterinary management and future research.

Data are presented on the duration of survival of platypus held in the collections of the 5 Australian zoos displaying the species over the period 1987-1991. Of 10 living platypus, five had survived for 7 or more years. Similarly, of 10 captive animals that died during the period, six had survived for 6 or more years. Five purpose-caught animals were integrated into captive collections over the period; all of these were alive at the end of 1991. The high survival of captive platypus documented in this study contrasts with the conclusion of Whittington (1991) that the duration of survival of platypus in captivity is generally short. This primarily reflects differences in the nature of the two sets of data: Whittington's analysis was based on incomplete records dating back to 1934, and also categorised as 'managed in captivity' those wild platypus that died at zoos while under veterinary care. A series of recommendations on current captive management issues includes the need for improved veterinary knowledge of platypus.

Animals↗

PubMed1996

Ultrastructure, number, distribution and innervation of electroreceptors and mechanoreceptors in the bill skin of the platypus, Ornithorhynchus anatinus.

The platypus is presently the only mammal demonstrated to use electroreception to obtain food. The electroreceptive system of the platypus is far more complex than that of its close relative the echidna. This paper presents an anatomical study of the basis of electroreception in the platypus. The innervation of the bill by the trigeminal nerve is described, as are three sensory structures, associated with food gathering, within the bill skin. There are 40,000 mucous gland electroreceptors found in the bill skin of the platypus. The papillary portion of each of these sensory mucous glands is modified to accommodate electrosensory nerve terminals. In contrast to fish electroreceptors, the electrosensory terminals of the platypus are not associated with a sensory cell. These mucous gland electroreceptors are arranged in a series of parasagittal stripes on the bill. This array suggests a basis for the ability of the platypus to quickly and accurately locate the origin of an electrical stimulus. A push-rod mechanoreceptor, similar in morphology to Eimer's organ of the mole, and bill-tip organs in birds, was also found in the bill skin. The slightly differing morphology of these mechanoreceptors when compared to their avian and talpid counterparts suggests that this is another example of convergent evolution, with the common need to provide a solution to increasing tactile sensitivity on bare rhinarial skin. These push-rods are found to be most dense around the labial margins of the bill, with a marked decrease in density towards the middle and caudal portions of the bill. The distribution of the push-rods is similar to the distribution of the third sensory structure found on the bill, the sensory serous gland. Although less numerous than the mechanoreceptors (46,500 mechanoreceptors compared with 13,500 sensory serous glands), these sensory serous glands have a similar distribution and similar changes in density. These concurrent distributions argue for some functional correlation of these two sensory structures. The papillary region of the serous gland is modified in a manner similar to that of the mucous gland electroreceptor to accommodate sensory input. The sensory terminals of the serous glands are very similar to those of the mucous gland electroreceptors, and so it is presumed that these sensory serous glands are a type of electroreceptor that might be involved in detection of electrical signals at close quarters where the mechanoreceptors are also engaged.

Animals↗

PubMed1999

Isolation of Mucor circinelloides from a case of ulcerative mycosis of platypus (Ornithorhynchus anatinus), and a comparison of the response of Mucor circinelloides and Mucor amphibiorum to different culture temperatures.

The fungus Mucor circinelloides was isolated from a platypus (Ornithorhynchus anatinus) suffering from ulcerative mycosis. On horse blood agar at 20, 25 and 30 degrees C, the fungus formed sphaerule-like bodies, a morphology previously associated with Mucor amphibiorum, the species thought to be responsible for the disease in platypus. A biopsy taken from the ulcer was fixed, cut and stained. The sections were compared with sections taken from other platypuses suffering from ulcerative mycosis, and from which M. amphibiorum had been isolated. There were no discernible differences between the sphaerule-like bodies found in any of the sections. The presence of sphaerule-like bodies in tissues of ulcerated animals can, therefore, probably no longer be relied upon as a definitive method for the diagnosis of M. amphibiorum infection. It is possible that M. circinelloides is either a primary or a secondary pathogen of platypuses, and further work is required to resolve this point. The isolate of M. circinelloides grew at temperatures up to 38 degrees C, with an optimum temperature for growth of 30 degrees C. Of six isolates of M. amphibiorum derived from both platypus and amphibians, two grew well at 38 degrees C. The growth of one of these isolates at elevated temperatures may be explained by the hot climate of the area in Queensland in which it was found. All of the isolates tested had maximum temperatures for growth in excess of the body temperature of platypuses (32 degrees C).

Animal Diseases↗

PubMed2002

Evidence for an early appearance of modern post-switch immunoglobulin isotypes in mammalian evolution (II); cloning of IgE, IgG1 and IgG2 from a monotreme, the duck-billed platypus, Ornithorhynchus anatinus.

To trace the emergence of the modern post-switch immunoglobulin (Ig) isotypes in vertebrate evolution we have studied Ig expression in mammals distantly related to eutherians. We here present an analysis of the Ig expression in an egg-laying mammal, a monotreme, the duck-billed platypus (Ornithorhynchus anatinus). Fragments of platypus IgG and IgE cDNA were obtained by a PCR-based screening using degenerate primers. The fragments obtained were used as probes to isolate full-length cDNA clones of three platypus post-switch isotypes, IgG1, IgG2, and IgE. Comparative amino acid sequence analysis against IgY, IgE and IgG from various animal species revealed that platypus IgE and IgG form branches that are clearly separated from those of their eutherian (placental) counterparts. However, the platypus IgE and IgG still conform to the general structure displayed by the respective Ig isotypes of eutherian and marsupial mammals. According to our findings, all of the major evolutionary changes in the expression array and basic Ig structure that have occurred since the evolutionary separation of mammals from the early reptile lineages, occurred prior to the separation of monotremes from marsupial and placental mammals. Hence, our results indicate that the modern post-switch isotypes appeared very early in the mammalian lineage, possibly already 310-330 million years ago.

Amino Acid Sequence↗

PubMed1990

"Intermediate zone" of mammalian spleens: light and electron microscopic study of three primitive mammalian species (platypus, shrew, and mole) with special reference to intrasplenic arteriovenous communication.

The intermediate zone (IZ) of nonperfused and perfused spleens in three species of primitive mammals (shrew, mole, platypus) was studied morphologically. The IZ is a tissue zone consisting of plexiform vessels, probably venous capillaries, and is located transitionally between the white and red pulp. The IZ is separated from the white pulp by the arterial net (AN), in which the white pulp arteries terminate. Development of the IZ differs between the three species examined being distinctive in the platypus and shrew. The IZ is thin in the mole spleen. A closed type of arteriovenous (A-V) anastomosis was demonstrated in or around the IZ in the two Insectivora species examined. In the shrew spleen, peripheral arterial branches running within the IZ anastomose with the AN around the follicle. The AN anastomoses eventually with venous plexiform vessels of the IZ around the nonfollicular area of the white pulp to form a closed system. In the mole spleen, A-V anastomoses were noted between white pulp arteries (follicular and AN) and veins of the red pulp, either by direct communication or through fenestrated IZ vessels compatible with the plexiform vessels of the shrew spleen. A-V anastomosis in the IZ is probable, but not confirmed, in the platypus spleen, as analysis was limited to a nonperfused specimen. Well-developed ellipsoids were noted around arterial terminals of the IZ in the shrew spleen. Ellipsoids were also noted around all arterial terminals of the mole spleen directed to the red pulp. Most ellipsoids of the mole spleen appeared located within the IZ. No ellipsoids were present around arterial terminals of the IZ in the platypus spleen. Closed circulation was noted in terminals of the pulp artery in spleens of all three species. All pulp arteries of the mole spleen are postellipsoid segments of white pulp (AN and follicle) arteries. No ellipsoids were found around terminals of the pulp artery (penicillar artery) in shrew and platypus spleens. The IZ is probably homologous to the perilymphatic sinusoid (vein) of the lungfish spleen and may be regarded as part of the red pulp. The IZ may be representative of primitive mammalian spleens that have closed circulation. The marginal zone (MZ) of common mammalian spleens is probably a modified IZ by differentiation (remodelling) of the intrasplenic vein. In this process, withdrawal of venous vessels from the IZ occurred, leaving a lymphoreticular zone with open circulation (MZ). The marginal sinus reported in some mammalian spleens is probably a modified AN formed during this process. Possible morphological alterations of the spleen in vertebrate phylogeny are discussed.

Animals↗

PubMed2005

Chromosome chains and platypus sex: kinky connections.

Mammal sex determination depends on an XY chromosome system, a gene for testis development and a means of activating the X chromosome. The duckbill platypus challenges these dogmas.(1,2) Gutzner et al.(1) find no recognizable SRY sequence and question whether the mammalian X was even the original sex chromosome in the platypus. Instead they suggest that the original platypus sex chromosomes were derived from the ZW chromosome system of birds and reptiles. Unraveling the puzzles of sex determination and dosage compensation in the platypus has been complicated by the fact that it has a surplus of sex chromosomes. Rather than a single X and Y chromosome, the male platypus has five Xs and five Ys.

Animals↗

PubMed1993

Isolation, partial characterisation, and amino acid sequence of alpha-lactalbumin from platypus (Ornithorhynchus anatinus) milk.

alpha-Lactalbumin was isolated from the whey fraction of platypus (Ornithorhynchus anatinus) milk by successive ion-exchange, hydrophobic interaction and gel-permeation chromatography. The purified protein modified the action of partially-purified galactosyltransferase from platypus milk to promote the synthesis of lactose, but had very little modifier effect on bovine galactosyltransferase. Platypus alpha-lactalbumin has 126 amino-acid residues (molecular mass about 14.3 kDa), including a three-residue insertion not found in other alpha-lactalbumins or c-type lysozymes. It appears to have two sites of post-translational modification, of which at least one is N-glycosylated, to give an apparent molecular mass of 23 kDa on SDS-PAGE. The platypus sequence shows a high degree of positional identity (41-48%) with the alpha-lactalbumins of other species. Although it has no lysozyme activity, platypus alpha-lactalbumin is more similar to mammalian lysozymes than is any eutherian or marsupial alpha-lactalbumin, suggesting that this monotreme protein has evolved more slowly than other alpha-lactalbumins.

Amino Acid Sequence↗

PubMed2005

Cyto- and chemoarchitecture of the sensory trigeminal nuclei of the echidna, platypus and rat.

We have examined the cyto- and chemoarchitecture of the trigeminal nuclei of two monotremes using Nissl staining, enzyme reactivity for cytochrome oxidase, immunoreactivity for calcium binding proteins and non-phosphorylated neurofilament (SMI-32 antibody) and lectin histochemistry (Griffonia simplicifolia isolectin B4). The principal trigeminal nucleus and the oralis and interpolaris spinal trigeminal nuclei were substantially larger in the platypus than in either the echidna or rat, but the caudalis subnucleus was similar in size in both monotremes and the rat. The numerical density of Nissl stained neurons was higher in the principal, oralis and interpolaris nuclei of the platypus relative to the echidna, but similar to that in the rat. Neuropil immunoreactivity for parvalbumin was particularly intense in the principal trigeminal, oralis and interpolaris subnuclei of the platypus, but the numerical density of parvalbumin immunoreactive neurons was not particularly high in these nuclei of the platypus. Neuropil immunoreactivity for calbindin and calretinin was relatively weak in both monotremes, although calretinin immunoreactive somata made up a large proportion of neurons in the principal, oralis and interpolaris subnuclei of the echidna. Distribution of calretinin immunoreactivity and Griffonia simplicifolia B4 isolectin reactivity suggested that the caudalis subnucleus of the echidna does not have a clearly defined gelatinosus region. Our findings indicate that the trigeminal nuclei of the echidna do not appear to be highly specialized, but that the principal, oralis and interpolaris subnuclei of the platypus trigeminal complex are highly differentiated, presumably for processing of tactile and electrosensory information from the bill.

Animals↗