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At least 469 records · Page 26Linked to original sources
PubMed1987

Thyroid development in the marsupial bandicoot, Isoodon macrourus.

The postnatal structural development of the thyroid gland of the Australian native bandicoot, Isoodon macrourus, was monitored and the onset of thyroid function (i.e., the secretion of thyroid hormones) was determined. Thyroid glands were obtained from bandicoots at days 1, 3, 11, 12, 13, 21, 25, 30, 34, 35, 39, 46, 48, 50, 59, 61, 75, 79, 83, and 163 of age and from adult animals, and the tissues were examined with the transmission electron microscope. The thyroid gland of the newborn bandicoot consisted of undifferentiated cells with no lumen. Follicles were first observed at day 12 postpartum, after which time rapid follicular growth occurred. The first signs of thyroid hormone secretion were seen at day 30 postpartum. A peak in thyroid activity seemed to occur around day 50 postpartum, and it correlated with the rapid rate of development of thermoregulatory capacity and hair development which occurred over the last 2 weeks of pouch life.

Aging↗
PubMed1988

Ultrastructure of the olfactory system of three newborn marsupial species.

The ultrastructure of the olfactory apparatus of three newborn marsupial species, the northern native cat, the brushtail possum, and the northern brown bandicoot, were examined. The olfactory epithelium and olfactory bulbs were at a similar stage of development in all three species. Receptor cells with cilia were observed, and although the olfactory system undergoes further differentiation during pouch life and although the olfactory epithelium and bulb of the newborn differs from that of the adult, these facts do not preclude the ability of the newborn to detect smell. The presence of touch receptors around the mouth region and of sensory cells within the olfactory epithelium would suggest that touch and smell are two of the senses allowing the newborn marsupial to reach the pouch.

Animals↗
PubMed1989

Vestibular system of the newborn marsupial cat Dasyurus hallucatus.

The ultrastructure of the ear of the newborn native cat was examined to determine whether the vestibular system contained sensory receptors. A sensory region, presumably the utricle, was identified in each ear and consisted of a discrete population of otoliths overlying a sensory epithelium which possessed kinocilia and stereocilia. The remainder of the vestibular system did not appear to be developed anatomically. The newborn cat has rudimentary vestibular, olfactory, and mechanoreceptors (Merkel cells), and these structures may aid the newborn marsupial in the journey from the urogenital sinus to the pouch and in locating the teat.

Animals↗
PubMed1990

Absence of an osseous patella and other observations in Macropodidae stifle.

The patella is a large sesamoid bone that typically develops in the tendon of insertion of the large extensor muscles of the stifle joint. Although present in almost all species of mammals and birds, it has been found to be absent in the red kangaroo and two wallaby species (family Macropodidae). In its place is a fibrocartilage pad, located in the tendon of the quadriceps femoris muscle. This structure is visible grossly, is palpable, and has the form normally expected of a bony patella. In addition, the femoral trochlea is shallow and asymmetric, and the lateral gastrocnemius sesamoid is unusually prominent. These and other related modifications in the area of the Macropodidae stifle are presented.

Animals↗
PubMed1990

Absence of cartilage canals in the long bone extremities of four species of skeletally immature marsupials.

The cartilaginous epiphyses and physes from the bone extremities of four species of skeletally immature marsupials were studied. The microscopic and ultrastructural features of the marsupial tissues were compared with similar samples from a neonatal lamb and a 1-day-old chick. Chondrocyte differentiation and endochondral ossification appeared similar in physes from the marsupials, foetal lamb, and 1-day-old chick. However, unlike the lamb and chick, which both contained cartilage canals, there were no cartilage canals in the epiphyseal or physeal cartilage from the marsupials. Many of the epiphyseal chondrocytes from the marsupial specimens contained large lipid droplets. It is suggested that the lipids in marsupial chondrocytes may be utilized in metabolic pathways. Despite hypertrophy of chondrocytes, there were no epiphyseal ossification centers in the femoral heads of the marsupial specimens; this was possibly due to the absence of cartilage canals, which are considered a source of osteoproginator cells. This study indicates that physeal and epiphyseal cartilage in marsupials is viable and functions in an avascular environment; this may be due to unique metabolic properties of the chondrocytes.

Animals↗
PubMed1991

Cervical lymph nodes and mast cells in the marsupial Sminthopsis crassicaudata.

A study of the cervical lymph nodes from the fat-tailed dunnart, Smithopsis crassicaudata, revealed the nodes were pigmented with lipofuscin and contained many large cells which were identified as mast cells from their ultrastructure and histochemical staining properties. It is believed that the very high density of mast cells in the cervical lymph nodes contributed to an increase in size of these organs compared to other animals. Very high levels of histamine (90 micrograms/g) were found in the nodes. Cervical lymph nodes with these unusual features were found not only in healthy, umprimed laboratory bred adults, but also in pouch young, wild caught animals, and adults of the closely related species, Sminthopsis macroura. A comparison of the histochemical and ultrastructural characteristics of mast cells from various organs of adult S. crassicaudata was also made. Mast cells from lymph node, skin, tongue, salivary glands, intestinal mucosa, and spleen showed slight variations in staining and structure.

Animals↗
PubMed1992

Development of the vestibular and auditory system of the northern native cat, Dasyurus hallucatus.

The developing vestibular and auditory system of the native cat Dasyurus hallucatus was examined from birth to day 55 postpartum to determine when the six sensory regions had an adult structure. The utricle, a sensory epithelium with an overlying discrete population of otoliths, was present in the newborn native cat. The saccule, which has a similar structure to the utricle, and the three crista ampullaris of the semicircular canals, were present by day 21 postpartum. The organ of Corti was formed by day 50 and the external ear duct was patent by day 55 postpartum. Hair is first seen on the native cat by day 45 when the young first leave the pouch. They are left in the nest and travel on the back of the lactating mother until about day 80. The eyes open on approximately day 75. Thus, the native cat has fully functional visual, auditory, and vestibular systems when the juvenile leaves the nest.

Age Factors↗
PubMed1993

Why do spermatozoa of American marsupials form pairs? A clue from the analysis of sperm-pairing in the epididymis of the grey short-tailed opossum, Monodelphis domestica.

In order to understand the evolutionary significance of sperm-pairing in American marsupials, an ultrastructural investigation was made of this process in the South American grey short-tailed opossum, Monodelphis domestica. One epididymis from each animal (5) was fixed for light and electron microscopy and divided into 18 segments. The contralateral tract was divided into similar segments and assessments made of the total number of spermatozoa and the proportion of sperm-pairs. The mean total sperm number was 4.20 +/- 0.62 x 10(6)/epididymis. Sperm-pairing commenced around segment 9 in the proximal corpus epididymidis and reached a maximum of 80% in the caudal sperm storage region of the duct. The sperm-pairing process was characterised by four stages. Spermatozoa exhibited parallel alignment as indicated by the positioning of identical cross-sections of sperm heads. This was followed by close apposition with acrosomal faces parallel rather than opposite. Rotation of the sperm heads around each other then apparently occurred as indicated by the morphological alignment of sections of paired sperm heads. Sperm-pairing was complete when the acrosomal faces were precisely aligned and joined. Misalignment and failure to pair was observed in about 20% of spermatozoa in the cauda epididymis. Such a complex sperm-pairing process may ensure that conjugated spermatozoa are precisely aligned so that flagella movement can be accurately coordinated for maximal progressive motility.

Acrosome↗
PubMed1994

Embryonic-maternal cell interactions at implantation in the fat-tailed dunnart, a dasyurid marsupial.

BACKGROUND: In marsupials implantation occurs about two-thirds the way through the short gestation before which time the embryo is surrounded by the permeable shell membrane which prevents physical contact between the trophoblast and uterine epithelium. Although the trophoblast has been shown to be invasive to varying degrees in several species of marsupials, the ultrastructure of the embryonic-uterine cell interactions at the time of implantation has not been described in this group. METHODS: Thick plastic sections and transmission electron microscopy were employed to investigate the cellular interactions at implantation in the fat-tailed dunnart (Sminthopsis crassicaudata), a dasyurid Australian marsupial. RESULTS: Our results show that epithelial penetration begins when the embryo is at the late presomite/early somite stage. In the trilaminar region of the yolk sac (TYS), trophoblast cells adjacent to the embryo form desmosomes with uterine epithelial cells and also appear to fuse with them to form hybrid cells, the cytoplasm of which resembles that of trophoblast. Later in the TYS, as the placenta develops, trophoblast microvilli and larger cell processes invaginate, and interdigitate with, the highly folded maternal epithelium but do not invade it. At this time in the bilaminar, or avascular, yolk sac (BYS), multinucleate trophoblast giant cells (TGCs) from an annular region adjacent to the sinus terminalis intrude between, and possibly fuse with, the maternal epithelium. The invading TGCs spread laterally above the residual basal lamina before migrating into the stroma. CONCLUSIONS: In this species of marsupial at least, the cell interactions at the time of implantation are similar to those seen in some eutherian species despite the fact that the fetal chorion is of yolk sac rather than allantoic origin.

Animals↗
PubMed1995

Central cardiovascular shunts in the perinatal marsupial.

BACKGROUND: Marsupials are born at an early stage of development after a short period of gestation. In this study the nature and timing of closure of the central cardiovascular shunts was investigated. METHODS: Light and scanning electron microscopy were used to determine changes in central cardiovascular shunts in eight marsupial species with gestation periods of between 12.5 and 36.5 days and birth weights ranging from 12.5 mg to 740 mg. Laboratory mice with a birth weight of about 1,000 mg and a gestation period of 21 days were included for comparison. RESULTS: Marsupials have a ductus arteriosus and an interatrial communication. The former closes rapidly after birth in the marsupial; however the interatrial communication is in the form of a fenestrated septum, which closes as a result of tissue proliferation over a period of days after birth. An additional central shunt, an interventricular foramen, was found to persist in three species for a short time after birth. In one species, the eastern native cat, Dasyurus viverrinus, which has a gestation period of about 19 days and low birth weight of about 12.5 mg, in addition to the two common shunts there was a large interventricular communication and septation of the outflow tract was incomplete. CONCLUSION: In adapting from intra-uterine life, it seems that marsupials have adopted different, but equally effective strategies, with regard to the circulatory system.

Animals↗
PubMed2006

Trophoblast and hypoblast in the monotreme, marsupial and eutherian mammal: evolution and origins.

The pregastrula stage mammalian conceptus consists of both embryonic and non-embryonic components. The latter forms the bulk of the tissues, provides nutrition for the developing embryo and also contributes developmental signals that influence events within the embryo itself. Understanding the origins and relationships between the embryonic and extraembryonic cell lineages is thus central to understanding development in mammals. Despite the apparent gross differences in early developmental strategy and form, the conceptuses of eutherian, marsupial and monotreme mammals show some remarkable similarities in the lineage allocation to trophoblast and hypoblast and in the emergent properties of the two cell types. We suggest that the gross differences can be explained by two relatively small evolutionary timing changes affecting cell adhesion patterns and the polarisation of developmentally significant information. These changes result in the conversion of a unilaminar blastocyst to a morula form composed of blastomeres with increased regulatory capacity.

Animals↗
PubMed1990

The cytoskeletal system of mammalian primitive erythrocytes: studies in developing marsupials.

Seeking to resolve conflicting literature on cytoskeletal structure in mammalian "primitive" generation erythrocytes, we have utilized the circulating blood of developing marsupials. In young of the Tammar Wallaby (Macropus eugenii) and the Gray Short-tailed Opossum (Monodelphis domestica), relatively large, nucleated primitive erythrocytes constituted nearly 100% of the circulating population at birth (= day 0) and in fetuses (Tammar) several days before birth. These cells were discoidal or elliptical, and flattened except for a nuclear bulge. Their cytoskeletal system, consisting of a marginal band of microtubules enclosed within a cell surface-associated network (membrane skeleton), closely resembled that of non-mammalian vertebrate erythrocytes. By day 2 or 3, much smaller anucleate erythrocytes of "definitive" morphology, lacking marginal bands, appeared in abundance. These accounted for greater than 90% of the circulating population of both species by day 6-8. Non-nucleated erythrocytes of a different type, constituting 1-6% of the cells in most blood samples up to day 7, were identified as anucleate primitives on the basis of size, shape, and presence of a marginal band. Thus, loss of erythrocyte nuclei in mammals appears to begin earlier than generally recognized, i.e., in the primitive generation. Counts of these anucleate primitives in young of various ages implicated nucleated primitives as their probable source. Pointed erythrocytes, occasionally found in younger neonates of both species, occurred in greatest number in fetuses (Tammar) prior to birth. This is in accord with previous work on non-mammalian vertebrates suggesting that such cells are morphogenetic intermediates. The results confirm the long-suspected similarity between mammalian primitive erythrocytes and the nucleated erythrocytes of all non-mammalian vertebrates.

Animals↗
PubMed1991

The identification of mammalian centrosomal antigens using human autoimmune anticentrosome antisera.

Human autoimmune sera were screened for the presence of anticentrosome autoantibodies. Two high titer sera were identified that reacted with HeLa, CHO, and PtK2 centrosomes by immunofluorescence, although the fluorescent patterns that were obtained using the two antisera were separate and distinct. Serum obtained from patient IJ contained antibodies that reacted with epitopes present only in mitotic centrosomes; staining of interphase centrosomes was never detected uing IJ antiserum. Immunoblot analysis demonstrated that antibodies present in IJ antiserum reacted with a 190 kD spindle pole antigen. Immunofluorescent staining of cultured mammalian cells demonstrated that antibodies present in serum obtained from patient SPJ reacted with both interphase and mitotic centrosomes. Characterization of SPJ antiserum by immunoblotting demonstrated that antibodies present in the SPJ serum recognized proteins of Mrs of 39, 185, and 220 kD, although the possibility that the 185 kD polypeptide was a proteolytic breakdown product of the 220 kD protein has not been eliminated. Neither antiserum was able to inhibit microtubule nucleation from centrosomes in a lysed cell system in which pure 6S tubulin was added to permeabilized cells following pretreatment of the cells with either SPJ or IJ antiserum. These antisera should be useful probes for studying the biochemistry of the mammalian centrosome.

Animals↗
PubMed1991

Inhibition of spindle elongation by taxol.

During anaphase B spindle elongation, interzonal microtubules lengthen to accomplish pole-pole separation, while at the same time remaining highly dynamic [Shelden and Wadsworth, J. Cell Sci. 97:273-281, 1990]. To further examine the role of microtubule polymerization and dynamics during spindle elongation, cells have been treated with taxol, which induces microtubule polymerization and stabilizes microtubules. Taxol was added to PtK1 cells 3 minutes after initial chromatid separation, so that the effect on anaphase B could be observed with minimal disruption to anaphase A movement. In 20 microM taxol, the rate and extent of pole-pole separation, measured from time-lapse video records, are reduced to 4% and 9.5% of controls, respectively. The organization of microtubules in taxol treated cells was examined using tubulin immunofluorescence and confocal fluorescence microscopy. Taxol induces a dramatic reorganization of interzonal microtubules resulting in a narrow gap, which is nearly completely lacking in MTs, across the center of the interzone. Furthermore, microtubules in taxol treated cells are resistant to nocodazole induced microtubule disassembly. Our results reveal that taxol rapidly inhibits anaphase B spindle elongation; inhibition is accompanied by a depletion of interdigitated interzonal microtubules and a reduction in microtubule dynamic behavior.

Alkaloids↗
PubMed1995

Cytochalasin J affects chromosome congression and spindle microtubule organization in PtK1 cells.

PtK1 cells were treated with 10 micrograms/ml cytochalasin J (CJ) for 15 min at various stages of mitosis. When applied at nuclear envelope breakdown (NEB) chromosome congression was blocked or substantially slowed, and chromosomes failed to show organization patterns typical of prometaphase. Spindle microtubule (MT) numbers appeared unaffected as judged by the pattern of birefringent retardation. However, ultrastructural analysis showed MTs to be reorganized within the spindle domain with some exhibiting fragmentation and others failing to interact with poorly defined kinetochore laminae. The spindle domain took on a curved, almost banana-like shape, as related to the position of the centrosomes and lack of orientation of chromosomes. Serial section analysis of kinetochore regions showed reduced contour length and maturation of the kinetochore plate with few MTs associated with this structure. Cells similarly treated with 10 micrograms/ml CJ at NEB for 15 min and then released into conditioned medium for 15 min showed the most chromosomes resumed congression to the metaphase plate. Ultrastructural analysis revealed a more normal organization of spindle MTs, but kinetochore structure remained affected. CJ treatment of cells in prometaphase slightly affected chromosomes congression with most chromosomes aligning at the metaphase plate after 10-15 min of treatment. Ultrastructural analysis showed that astral MTs were disrupted and spindle MTs were fragmented; few MTs coursed from kinetochore to pole. Kinetochore structure was also affected with only small numbers of short MTs seen associated with kinetochores. Application of CJ at anaphase onset had little effect on anaphase A and B, but cytokinesis failed to occur. Anti-tubulin staining of a monolayer of cells treated with 10 micrograms/ml CJ for 15 min showed that over 60% of mitotic figures exhibited changes in MT organization. Cells showing the greatest effect of treatment had several foci of bundles of MTs, as if the spindle were multipolar. Chromosomes were arranged near the periphery of the spindle which could be a result of abnormalities of kinetochore structure. Improper association of spindle MTs with kinetochores and, thus, changes in kinetochore position could account for these changes in spindle architecture.

Actins↗