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L Selwood

Publications and source records attributed to L Selwood.

At least 19 recordsLinked to original sources
PubMed2004

A developmental investigation of the liver, bone marrow and spleen of the stripe-faced dunnart (Sminthopsis macroura).

The development of the liver, bone marrow and spleen have been investigated in the stripe-faced dunnart. At birth, the liver was undergoing haematopoiesis but the level declined rapidly and by day 50 after birth the liver was histologically mature. Both the bone marrow and spleen were non-haematopoietic at birth but initiated haematopoiesis shortly thereafter. Bone marrow was initially detected at day 11 postpartum. By 57 days after birth, adipocytes had infiltrated the marrow and were abundant by day 60 after birth. Mitotic cells were observed in remaining areas of marrow until at least 170 days postpartum. The spleen at birth was undifferentiated, with trabeculae appearing by day 42. Red and white pulp areas became apparent by day 43 and were well defined by day 57 after birth. In summary, the pattern of the development of the liver, bone marrow and spleen in the stripe-faced dunnart were similar to that observed in eutherians and other metatherians studied to date.

Age Factors↗
PubMed2004

The appearance and distribution of mature T and B cells in the developing immune tissues of the stripe-faced dunnart (Sminthopsis macroura).

This paper describes the initial appearance and distribution of mature T and B cells in the developing immune tissues of the stripe-faced dunnart (Sminthopsis macroura) based on the use of species cross-reactive antibodies to the lymphocyte cell surface markers CD3, CD5 and CD79b. At birth no mature T or B cells were detected in the liver or bone marrow using anti-CD3, anti-CD5 or anti-CD79b antibodies. T cells were detected in the thymus with anti-CD3 by day 12 and anti-CD5 by day 50 postpartum, and T cells in the spleen were detected by day 43 and day 80 postpartum using anti-CD3 and anti-CD5, respectively. B cells were observed in the dunnart spleen by 43 days after birth. CD3- and CD79b-positive cells were detected in the lymph nodes by 50 days and CD5 by day 15 after birth, and in the gut-associated lymphoid tissues by day 50 and anti-CD5 by day 57 postpartum. The development and distribution of T and B cells in the immune tissues of dunnart pouch young is similar to that described in other marsupial species. Low numbers or absence of mature lymphocytes in immune tissues of early pouch young dunnarts further support the proposition that young marsupials are reliant on non-specific defence strategies and/or maternal strategies for a significant period of their time of development in the pouch.

Animals↗
PubMed2003

A histological investigation of the lymphoid and immunohaematopoietic tissues of the adult stripe-faced dunnart (Sminthopsis macroura).

This is the first published description of the lymphoid and immunohaematopoietic tissues of an Australian polyprotodont, the stripe-faced dunnart, Sminthopsis macroura and the first account of bronchus-associated lymphoid tissue (BALT) in a metatherian. Histologically, the tissue beds are similar in appearance to those reported in other adult eutherian and metatherian mammals. The liver and bone marrow were mature and virtually no haematopoietic activity was observed. The thymus had undergone involution but retained some lymphocytes. The spleen was similar to that observed in other metatherians containing areas of red and white pulp separated by a marginal zone. Lymph nodes, except for a pair in the posterior abdomen, were difficult to locate but were similar to those observed previously in other adult metatherians. Peyer's patches were present; however, they lacked dome regions and sometimes had villi above them. BALT appeared to be both compartmentalised and non-compartmentalised in the adult stripe-faced dunnart.

Animals↗
PubMed2003

Development of lymphoid tissues of the stripe-faced dunnart (Sminthopsis macroura).

The development of the lymphoid tissues of a model marsupial, the stripe-faced dunnart, has been described from birth to weaning, a period of 2.5 months. At birth the lymphoid tissues, including the thymus, lymph nodes and mucosa-associated lymphoid tissues, were undeveloped. A thoracic thymus consisting primarily of stromal tissue was observed by day 4 after birth but by day 12, lymphocytes were observed in the thymus and some cortico-medullary differentiation was apparent. Lymph nodes were histologically mature by day 31, the earliest day investigated for this tissue. In gut tissue, lymphoid follicles were first observed by day 57 post-partum. No bronchus-associated lymphoid tissue was observed in any lung samples. The thymus, lymph nodes and gut-associated lymphoid tissues were all distinguishable before weaning (day 70) but not all were histologically mature. The sequence of development of the lymphoid tissues in the stripe-faced dunnart was similar to those observed in other marsupial species.

Adipose Tissue↗
PubMed2003

Species differences in the ovarian distribution of 3beta-hydroxysteroid dehydrogenase/delta5-->4 isomerase (3beta-HSD) in two marsupials: the brushtail possum Trichosurus vulpecula and the grey, short-tailed opossum Monodelphis domestica.

The ovarian distribution of the steroidogenic enzyme 3beta-hydroxysteroid dehydrogenase/delta(5-->4) isomerase (3beta-HSD) was investigated by immunocytochemistry in two marsupial species throughout the reproductive cycle, using a rabbit polyclonal antibody raised against human placental 3beta-HSD. In the polyoestrous and polyovular South American opossum Monodelphis domestica, immunostaining was positive for 3beta-HSD in the adrenal cortex, the ovarian interstitial tissue, the corpus luteum and the granulosa cells of antral and atretic follicles. The theca interna was weakly positive for 3beta-HSD, but only in late preantral to early antral stages of follicular development. The adrenal medulla and smaller preantral follicles were completely negative for 3beta-HSD. In contrast, in the polyoestrous and monovular Australian brushtail possum Trichosurus vulpecula, immunostaining showed a strong positive reaction for 3beta-HSD in the theca, whereas the granulosa layer remained predominantly negative for 3beta-HSD except in the largest follicles. The atretic follicles were completely negative for 3beta-HSD. The ovaries of pregnant animals contained grossly enlarged, persistent, antral follicles, which reacted positively for 3beta-HSD. The function of these follicles in T. vulpecula and the 3beta-HSD-positive atretic follicles in M. domestica has not been determined. The differences between the two marsupials represent species variations. The situation in M. domestica does not represent a marsupial-eutherian dichotomy as previously conjectured.

3-Hydroxysteroid Dehydrogenases↗
PubMed2002

Localization of transforming growth factor beta2 (TGFbeta2) and its receptors, TbetaRI and TbetaRII, in uteri and blastocysts of the stripe-faced dunnart (Sminthopsis macroura) during gastrulation.

This study describes for the first time the spatial and temporal distribution of a growth factor and its receptors in uteri and conceptuses of a marsupial species during the peri-gastrulation period. Uteri (gravid and non-gravid) and blastocysts from 40 female stripe-faced dunnarts (Sminthopsis macroura) were collected over the peri-gastrula period (days 6.0-8.5) and stained immunohistochemically for transforming growth factor beta2 (TGFbeta2) and its receptors, TbetaRI and TbetaRII, to determine possible roles for TGFbeta2 in marsupial embryonic development. The events that occurred during the period examined included the appearance and proliferation of hypoblast and mesoderm, primitive streak and node formation, and early neurulation. Differences in TGFbeta2 quantities between gravid and non-gravid uteri reflect differences in uterine morphology, indicating a role for TGFbeta2 in endometrial remodelling. In blastocysts, large quantities of all three proteins in the trophectoderm during the node stage coincide with both blastocyst expansion before implantation and the appearance of multinucleated cells, indicating that TGFbeta2 plays a role in conceptus elongation and trophectoderm differentiation. In contrast, lack of TbetaRII in blastocysts during hypoblast formation and proliferation negates any role for TGFbeta2 in these processes, as both receptors are required for a response to TGFbeta2. High concentrations of TGFbeta2 but low concentrations of TbetaRII in blastocysts during early primitive streak formation indicate that paracrinal embryo-maternal signalling may be occurring, as blastocysts cannot respond to TGFbeta2 at this stage, but uteri could. A similar situation, but reversed, also occurs during primitive node formation.

Activin Receptors, Type I↗
PubMed2001

Founding editorial: embryology--an integrated approach.

We introduce the Embryology domain of TheScientificWorld and outline the scope and aims. We argue for an interdisciplinary approach to problems in develop-mental biology. Three areas are identified as being of particular relevance to this domain: evolutionary developmental biology, teratology, and descriptive or experimental embryology.

Animals↗
PubMed2001

Identification of a homologue of POU5F1 (OCT3/4) in a marsupial, the brushtail possum.

Several morphological features of early development differ between marsupials and eutherians. These include early overt conceptus polarity, the mode of segregation of pluriblast and trophoblast lineages, and the superficial position of the pluriblast within the unilaminar blastocyst epithelium. Knowledge of the molecular mechanisms of early development is lacking in marsupials. We have cloned from the brushtail possum, Trichosurus vulpecula, the partial cDNA of a marsupial homologue of mammalian POU5F1, which encodes octamer-binding transcription factor-4 (Oct-4). The 579 bp cloned coding sequence of possum POU5F1 (tvPOU5F1) shares 74, 78, and 79% identity with murine Pou5f1, human POU5F1, and bovine bPOU5F1, respectively, at the protein level. The mRNA for tvPOU5F1 was detected by in situ hybridization in oogonia and in oocytes of growing follicles, but not in early meiotic oocytes. In a gastrulation-stage conceptus, high tvPOU5F1 expression was found in the embryonic ectoderm, with low or undetectable expression in other cell types. These results are comparable with those of murine and bovine expression studies, and suggest that the putative role of POU5F1 in totipotent and pluripotent cells is conserved among mammals.

Amino Acid Motifs↗
PubMed2001

Ultrastructure of oogenesis in the brushtail possum.

Marsupial ova are slightly larger on average than those of eutherians. They have often been described as "yolky", although the nature and roles of their contents in later development are poorly understood. In the ova of all marsupial species studied, large quantities of electron-lucent vesicles are present. This study describes the ultrastructure of oogenesis in the brushtail possum, Trichosurus vulpecula. Oocytes of primordial follicles contain a variety of organelles of unknown function, some of which have been described previously in bandicoots. Large electron-lucent vesicles begin to accumulate after the transition from primordial follicle to primary follicle and are derived at least partly from the Golgi and endoplasmic reticulum. Other inclusions that are absent in some other marsupial species are present in growing possum oocytes in smaller quantities, including yolklike lipid bodies and electron-dense granular bodies.

Animals↗
PubMed2001

Oogenesis in the marsupial stripe-faced dunnart, Sminthopsis macroura.

The timetable of oogenesis in Sminthopsis macroura is accelerated like in other marsupials showing relatively early maturation of the female. On the day of parturition (day 0) migration of primordial germ cells to the indifferent gonads has been completed. Follicular growth seems not to correspond to the biphasic pattern, in which oocyte and follicle grow synchronously until antral stages when only the follicle increases in size, but shows a continuous growth of the oocyte and the follicle up to the time of ovulation. During primordial and early primary follicle stage a paranuclear complex is present in the oocyte, consisting mainly of smooth tubules of endoplasmic reticulum. Cortical granules appear early in oocytes in secondary follicles. The conspicuous inclusions in the antral follicle are the clusters of electron-lucent vesicles in the oocyte. These inclusions grow from multivesicular bodies (MVB), which are formed from Golgi and endoplasmic reticulum vesicles. Further increase in the size of MVB involves the incorporation of endocytic vesicles and the coalescence of larger vesicles. The polarized nature of the oocyte at ovulation is due in part to the to accumulation of these vesicles in the cytoplasm opposite the eccentrically placed nuclear material.

Animals↗
PubMed2001

Mechanisms for pattern formation leading to axis formation and lineage allocation in mammals: a marsupial perspective.

Developing patterns in early embryogenesis are analysed in conceptuses from several families, including Dasyuridae, Phalangeridae, Macropodidae and Didelphidae, in which cleavage has been examined in some detail. Features common to cleavage and blastocyst formation, and in some cases to hypoblast formation, are used to develop an outline of possible mechanisms leading to axis formation and lineage allocation. Relevant features that have been described only in some species are also included. It is suggested that certain features of marsupial cleavage establish patterns in the developing blastocyst epithelia, pluriblast, trophoblast and hypoblast that contribute to axis formation and lineage allocation. All marsupials examined had a polarized oocyte or conceptus, the polarity of which was related to the conceptus embryonic-abembryonic axis and, eventually, the conceptus dorsal-ventral axis and the formation of the pluriblast (future embryo) and trophoblast. The embryonic dorsal-ventral and anterior-posterior axes were established after the allocation of hypoblast and epiblast. Mechanisms that appear to result in patterning of the developing epithelia leading to axis formation and lineage allocation are discussed, and include sperm entry point, gravity, conceptus polarity, differentials in cell-zona, cell-cell and cell-type (boundary effects) contacts, cell division order during cleavage and signals external to the conceptus. A model of the patterning effects is included. The applicability of these mechanisms to other amniotes, including eutherian mammals, is also examined.

Animals↗
PubMed2001

Significance of serum early pregnancy factor concentrations during pregnancy and embryonic development in Sminthopsis macroura (Spencer) (Marsupialia: Dasyuridae).

Marsupial pregnancy differs from that in eutherians in duration, placentation and hormonal profile so much so that maternal recognition of pregnancy may not occur in polyovular marsupials. However, a comparison of gravid and non-gravid uteri reveals differences indicative of histological and physiological adaptations to pregnancy. In the present study, the hypothesis that embryo-maternal signalling occurs in polyovular marsupials was tested by examining serum from non-pregnant and pregnant Sminthopsis macroura for the presence of early pregnancy factor (EPF), a serum protein secreted by the ovary in response to the presence of a newly fertilized egg in the oviduct. EPF is detectable in the serum of pregnant, but not in non-pregnant, females in all eutherians studied to date. In the present study, EPF was detected in S. macroura serum by the rosette inhibition test during the first 9 days of the 10.7 day gestation period in this marsupial. However, EPF was not detected on day 10, just before parturition, or in non-pregnant or preovulatory animals. Immunohistochemical analysis of ovaries from gravid and non-gravid animals demonstrates that EPF is found in the capillaries, interstitial spaces and secretory cells of the corpus luteum. It is concluded that the spatiotemporal pattern of EPF activity described strongly indicates that maternal recognition of pregnancy in marsupials is mediated, at least in part, by EPF. Because the endocrinological milieu is the same in pregnant and non-pregnant marsupials, the possibility of using marsupials as an experimental system for studying EPF function unconfounded by hormonal effects is presented.

Animals↗
PubMed2001

Induced ovulation, mating success and embryonic development in the stripe-faced dunnart, Sminthopsis macroura.

Induced ovulation resulting in normal embryos is rare in marsupials. In this study natural and induced ovulations were compared in mature Sminthopsis macroura (n = 122). Comparison of maturation of preovulatory oocytes by ovarian histology and examination of oocytes removed from developing follicles in 12 ovaries of 23 animals receiving 0.058 iu equine serum gonadotrophin (eSG) g(-1) with ovaries of 12 animals undergoing natural cycles showed that oocyte maturation was significantly more irregular when it was induced (P < 0.001). Postovulatory stages were examined by estimating the number of eggs ovulated from ovarian histology, and by counting oviduct and uterine contents recovered after ovulation. S. macroura receiving 0.087 iu eSG g(-1) (n = 34), administered as one (n = 17) or two (n = 17) injections, were significantly (P < 0.05) more likely to ovulate (74%), mate (80%) and have conceptuses (66%) than were animals receiving 0.058 iu eSG g(-1) (12, 53 and 0%, respectively) (n = 17), and the values were similar to those in animals (n = 36) undergoing natural cycles (100, 81 and 56%, respectively). Induced ovulation using 0.087 iu eSG g(-1) yielded significantly (P < 0.05) more oocytes per ovary (20.8 +/- 8.5; combined data) than did ovulation in animals undergoing natural cycles (13.7 +/- 3.2) (ANOVA, t test). The responses of animals induced in different phases of the oestrous cycle with 0.087 iu eSG g(-1) were not significantly different (ANOVA) with respect to the number of corpora lutea per ovary, conceptuses per animal or days to ovulation after injection. However, the proportion of females that responded after receiving 0.058 iu eSG g(-1) in the luteal phase was significantly different from that in animals treated with the same dose in the intermediate phase (P < 0.01) and in non-cyclic females treated with 0.058 iu eSG g(-1) (P < 0.02). The main benefits of the treatment were that normal embryos resulted and that 70-78% of non-cyclic animals could be induced to ovulate.

Anestrus↗
PubMed2000

cDNA cloning, characterization, expression and recombinant protein production of leukemia inhibitory factor (LIF) from the marsupial, the brushtail possum (Trichosurus vulpecula).

A reverse transcription technique using RNA templates combined with polymerase chain reaction (RT-PCR) was used to clone the cDNA fragment encoding the amino acid sequence of mature LIF protein of the marsupial, the brushtail possum, Trichosurus vulpecula. A PCR product with expected size, of 546bp, and termed tvLIF, was obtained using cDNA reverse-transcribed from total RNA isolated from possum uterus. A genomic DNA fragment (about 650bp) between the specified primers was also amplified, indicating the similarity in structure and organization of this gene and LIF genes from studied eutherian species, although the full-length of its cDNA and genomic DNA needs to be further clarified. The deduced amino acid sequence of tvLIF shows a high level of sequence identity and similar molecular characteristics to eutherian LIF, which suggests similar biological actions of this molecule in this marsupial. Because the expression of LIF gene in other mammalian species has been found to be at very low levels and its transcripts cannot be detected by Northern hybridization analysis, the expression pattern of tvLIF in adult tissues and reproductive tracts during early development was investigated using the RT-PCR technique. Resultant products of the RT-PCR were further analyzed by Southern hybridization using tvLIF as a probe. tvLIF transcripts were detected in most of the adult tissues and in the reproductive tracts of pregnant females. These results lend support to the idea that LIF contributes to the maintenance of pregnancy in this marsupial.

Amino Acid Sequence↗
PubMed2000

Marsupial egg and embryo coats.

Egg and embryo coats of marsupials are reviewed. Marsupial eggs are enclosed by a zona pellucida, mucoid coat and an outer shell coat. An extra-cellular matrix coat that lines the zona pellucida also occurs in some species. The zona pellucida consists of three zona proteins (ZPA, ZPB, ZPC) with considerable similarity to those of eutherian mammals. The zona is thought to be the sperm receptor site and, in some species, but not others, is a barrier to polyspermy. Immunostaining, in situ hybridisation, histochemistry and electron microscopy indicate that the zona originates in the oocyte at the onset of oocyte growth. It changes greatly in shape during ovulation and early development and plays an essential role in blastocyst formation. The mucoid coat is an acid glycoprotein that is produced by non-ciliated cells at all levels of the oviduct and has been implicated in providing a barrier to polyspermy, nourishment of the embryo and an osmotically stable environment for the embryo. Its width varies widely in marsupials. The shell coat is secreted by the epithelia of the utero-tubal junction and upper uterus during oestrus and early cleavage. Evidence is provided for a second wave of secretion at bilaminar and trilaminar blastocyst stages. Shell-free embryos do not survive in vitro during bilaminar and early trilaminar blastocyst stages. Hatching from the shell coat occurs between 65 and 85% of the gestation period usually when the embryo is undergoing early somitogenesis. The extra-cellular matrix is secreted by the oocyte or by the cells of early cleavage stages and initially separates cells from the zona pellucida and from each other. It plays an essential role in blastocyst formation. The zona, mucoid and shell coats provide a framework for blastocyst construction and normal embryos do not form in their absence in some species.

Animals↗
PubMed2000

A staging scheme for assessing development in vitro of organogenesis stage embryos of the stripe-faced dunnart, Sminthopsis macroura (Marsupialia: dasyuridae).

The inaccessibility of mammalian organogenesis stage embryos has precluded their widespread use in embryological and teratological studies. As organogenesis occurs during the last 1.5 days of the 10. 7 days of gestation in the stripe-faced dunnart (Sminthopsis macroura), the aim of the present study was to investigate whether day 9 and day 10 embryos and fetuses could be grown to term in vitro. High glucose Dulbecco's modified Eagle's medium with 10% fetal calf serum (FCS) supported embryonic growth for various periods of time, some to within 5 h of the predicted time of parturition. A roller culture system maintained at 35 degrees C was used to incubate organogenesis stage embryos (n = 43). Nine unincubated (control) embryos were either fixed for microscopic analysis or frozen for microprotein determination. The results of the present study indicate that with some optimization of the culture conditions (increasing oxygen in the gas phase in the culture tubes, replacing FCS with rat serum), it might be possible for organogenesis stage S. macroura embryos to be grown to term. A scoring scheme for assessing morphological development was devised for use as a standard in staging organogenesis stage embryos. This scheme reflects the highly compressed schedule of developmental events that occurs mainly during day 9 of gestation in S. macroura embryos. In comparison, during embryogenesis in Didelphis virginiana these developmental events occur from day 8 to day 10.5 of gestation, and birth occurs on day 13.

Animals↗
PubMed1998

An ultrastructural study of the role of an extracellular matrix during normal cleavage in a marsupial, the brushtail possum.

In marsupials, the mechanisms of lineage allocation into pluriblast and trophoblast are related to conceptus polarity and polarized discharge of extracellular matrix (ECM). The brushtail possum, Trichosurus vulpecula, a major pest species in New Zealand, is being intensively studied to develop an immunocontraceptive control method. Of 23 specimens examined, 11 were examined by electron microscopy to study the presence and role of the ECM in lineage allocation in the possum. A number of polarized features in the zygote identified the future embryonic and abembryonic poles. Pronuclei, in a broad band of mitochondrion-rich cortical cytoplasm, lay in the embryonic hemisphere, and numerous electron-lucent vesicles characterized the abembryonic cytoplasm. These vesicles seemed to contribute to the ECM. During cleavage, cells lay near the zona in the embryonic hemisphere, and ECM accumulated chiefly in the abembryonic hemisphere. Cell-zona adhesion facilitated by microvillous and club processes occurred at the early 4-cell stage, and cell-cell adhesion commenced at the late 4-cell stage. The first two cleavages were meridional, equal, and accompanied by elimination into the cleavage cavity of much of the electron-lucent vesicular material in the form of several membrane-bound yolk masses. The third cleavage was unequal, with both meridional and latitudinal planes. The first differences between trophoblast and pluriblast lineages appeared at the 8-cell stage. Later cleavage planes were latitudinal or oblique. Conceptus polarity, polarized discharge of ECM, and localized cell-zona adhesion were related to the first lineage allocation in the possum.

Animals↗