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PubMed1992

The development of righting reflexes in the pouch young of the marsupial Dasyurus hallucatus.

The development of righting was studied in the young of Dasyurus hallucatus, a small marsupial from northern Australia. Young were tested from birth to weaning. Righting began at 40 days, when tactile input on the snout triggered rotation to prone. Over the next 15-20 days, asymmetrical tactile input on the body triggered righting movements by the hindlegs (and later by the forelegs). Vestibular righting reflexes developed after these tactile righting reflexes. Furthermore, asymmetrical vestibular righting (i.e., when the young are held laterally in the air) developed before symmetrical vestibular righting (i.e., when held downward by the pelvis or placed supine in water). Vestibular righting triggered by falling supine in the air did not develop until about 80 days. This study further demonstrates that righting behavior does not consist of a single, integrated motor pattern, but a suite of motor patterns having independent control mechanisms and patterns of development.

Aging↗
PubMed2004

Comparative analysis of neural crest cell death, migration, and function during vertebrate embryogenesis.

Cranial neural crest cells are a multipotent, migratory population that generates most of the cartilage, bone, connective tissue and peripheral nervous system in the vertebrate head. Proper neural crest cell patterning is essential for normal craniofacial morphogenesis and is highly conserved among vertebrates. Neural crest cell patterning is intimately connected to the early segmentation of the neural tube, such that neural crest cells migrate in discrete segregated streams. Recent advances in live embryo imaging have begun to reveal the complex behaviour of neural crest cells which involve intricate cell-cell and cell-environment interactions. Despite the overall similarity in neural crest cell migration between distinct vertebrates species there are important mechanistic differences. Apoptosis for example, is important for neural crest cell patterning in chick embryos but not in mouse, frog or fish embryos. In this paper we highlight the potential evolutionary significance of such interspecies differences in jaw development and evolution. Developmental Dynamics 229:14-29, 2004.

Ambystoma↗
PubMed2006

Craniofacial development in marsupial mammals: developmental origins of evolutionary change.

Biologists have long studied the evolutionary consequences of the differences in reproductive and life history strategies of marsupial and eutherian mammals. Over the past few decades, the impact of these strategies on the development of the marsupial embryo and neonate has received attention. In this review, the differences in development in the craniofacial region in marsupial and eutherian mammals will be discussed. The review will highlight differences at the organogenic and cellular levels, and discuss hypotheses for shifts in the expression of important regulatory genes. The major difference in the organogenic period is a whole-scale shift in the relative timing of central nervous system structures, in particular those of the forebrain, which are delayed in marsupials, relative to the structures of the oral-facial apparatus. Correlated with the delay in development of nervous system structures, the ossification of the bones of the neurocranium are delayed, while those of the face are accelerated. This study will also review work showing that the neural crest, which provides much of the cellular material to the facial skeleton and may also carry important patterning information, is notably accelerated in its development in marsupials. Potential consequences of these observations for hypotheses on constraint, evolutionary integration, and the existence of developmental modules is discussed. Finally, the implications of these results for hypotheses on the genetic modulation of craniofacial patterning are presented.

Animals↗
PubMed1997

Informative enzyme/probe combinations for the multilocus DNA fingerprinting of marsupials.

DNA fingerprinting has become an invaluable tool in the study of population genetics, paternity success, and individual identification; however, the species specificity of some methods has made the wide-range screening of many different species very time-consuming. In this study we describe the development and application of reliable and informative DNA fingerprinting techniques in a range of marsupial species using three different restriction enzyme and two oligonucleotide probe combinations. Six species from four marsupial families, the koala (Phascolarctidae), tammar wallaby (Macropodidae), southern hairy-nosed wombat (Vombatidae), kowari, and dusky and brown marsupial mice (Dasyuridae) were examined. Restriction enzymes HinfI AluI and HaeIII were used in combination with the digoxygenin (DIG)-labelled oligonucleotide probes (CAC)5 and (GGAT)4. The combinations of HinfI/(GGAT)4, AluI/ (CAC)5 and AluI/(GGAT)4 were the most informative, providing highly resolved bands, low background, and the lowest band sharing between individuals. The genetic diversity evident within the different species showed a clear relationship between the level of band sharing and population size. The greatest levels of band sharing were found in the kowaris (80%), which were part of a long-term captive colony originating from a few founders, and the lowest levels of band sharing were found in the marsupial mice (30-35%) and tammar wallaby (45%), which were caught from large outbred wild populations.

Animals↗
PubMed1990

A simple pneumatic device for plunge-freezing cells grown on electron microscopy grids.

A detailed design for a simple and inexpensive variable-speed (1.0-5.8 m s-1) pneumatic plunge-freezing device is presented. Cultured cells, grown on Formvar-coated 75-mesh gold finder grids, are pneumatically driven into a stirring mixture of propane/isopentane (3:1) cooled by liquid nitrogen (LN2). Premature freezing of the sample in the cryogenic vapors above the cryogen is prevented by plunging through an entry tube into an insulating box, to which a partial vacuum is applied. The cryogenic vapors are drafted into the box at the level of the liquid cryogen by the vacuum, thereby preventing a layer of cold gas from collecting above the cryogen. To prevent the sample from thawing during transfer from the cryogen to the substitution medium, the box top is removed and compressed air is forced through a corrugated tube running the length of the box. The resulting boiling LN2 creates an atmosphere below -120 degrees C in which the transfer can be accomplished.

Animals↗
PubMed2001

Sex determining genes and sexual differentiation in a marsupial.

The role of genes in the differentiation of the testis and ovary has been extensively studied in the human and the mouse. Despite over a decade of investigations, the precise roles of genes and their interactions in the pathway of sex determination are still unclear. We have chosen to take a comparative look at sex determination and differentiation to gain insights into the evolution and the conserved functions of these genes. To achieve this, we have examined a wide variety of eutherian sex determining genes in a marsupial, the tammar wallaby, to determine which genes have a conserved and fundamental mammalian sex determining role. These investigations have provided many unique insights. Here, we review the recent molecular and endocrine investigations into sexual development in marsupials, and highlight how these studies have shed light on the roles of genes and hormones in mammalian sex determination and differentiation.

Animals↗
PubMed1983

Developmental aspects of X chromosome inactivation in eutherian and metatherian mammals.

The single active X principle has served for two decades as a focal point for research on the cyclic activation and inactivation of gene loci. Differences in X chromosome inactivation patterns of eutherian and marsupial mammals provide probes for investigating the mechanisms of the X inactivation process. In eutherian mammals, the X chromosome is inactivated early in meiotic prophase in males and remains inactive throughout the rest of spermatogenesis. During meiosis in females, the inactive X chromosome is activated so that both X chromosomes are active in oocytes. During the early cleavage divisions of female embryos, the paternally derived X is activated. It and the maternally derived X remain active until differentiation begins in early embryogenesis. At that time, the paternally derived X is inactivated in cells that give rise to extraembryonic membranes, whereas a random process determines which X chromosome is inactivated in cells that give rise to the embryo itself. Although less is known about developmental aspects of X inactivation in female marsupials, it is clear that the paternal X is preferentially inactive in postembryonic somatic cells. Furthermore, the paternal X is partially active at some loci in some cell types, indicating that it is not regulated as a single unit. The successful adaptation of a small (80-150 g), fecund marsupial to simple laboratory conditions now enables extensive experimentation on the large number of marsupials at various developmental stages. This capability, coupled with the application of newly developed cellular and molecular techniques to questions about X chromosome inactivation, shows great promise for advancing our understanding of the mechanisms that control the cyclic behavior of X chromosome activity.

Animals↗
PubMed1989

Functional organization of cerebral microvasculature in a marsupial, the northern quoll (Dasyurus hallucatus).

Capillaries within the central nervous system (CNS) of eutherian mammals form meshworks with numerous anastomoses, whereas capillaries in the CNS of marsupials consist entirely of hairpin-like loops, without anastomotic interconnections. Counter-current blood flow in capillary loops may have been important in the evolutionary development of a cerebral vascular supply. However, loops are not found in eutherian mammals, perhaps because of a limited benefit to the diffusive conductance of gases.

Animals↗
PubMed1989

The role of refractorinesss to long daylength in the annual reproductive cycle of the female Bennett's Wallaby (Macropus rufogriseus rufogriseus).

The beginning of the breeding season of the female Bennett's wallaby occurs when seasonal quiescence terminates 1-2 months after the summer solstice. In this study, the role of photoperiod in terminating seasonal quiescence was examined. One week before the summer solstice, five non-lactating wallabies were transferred from natural to artificial summer solstice daylength for 5 months. The beginning of the breeding season in these animals as indicated by births, matings, and peripheral progesterone profiles was not different from that of five control animals maintained on natural photoperiod. The following year, three animals were transferred from natural to summer solstice daylength on February 25 and were held on the artificial photoperiod until September 30. Changes in plasma progesterone concentrations indicative of the beginning of the breeding season occurred on June 12-30 (range), which was significantly (P less than 0.01) advanced by 29 days when compared with six control animals. These results indicate that the decrease in daylength that occurs after the summer solstice is not required to induce the termination of seasonal quiescence at the beginning of the breeding season. Further, the beginning of the breeding season can be advanced by transferring animals to long daylength early in seasonal quiescence. Photorefractoriness to long daylengths may therefore be important in the initiation of the breeding season in this species. In further experiments, groups of six animals were transferred from natural to artificial summer solstice daylength on September 26 and December 9 and pouch young were removed 7 days after the transfer. In September, reactivation of the quiescent corpus luteum followed soon after removal of pouch young (RPY) indicating that exposure to long daylength had not induced a transition into seasonal quiescence. In December, RPY was not followed by reactivation of the quiescent corpus luteum indicating that animals were in seasonal quiescence. These results suggest that the female Bennett's wallaby may need to experience a period of shortening days after the summer solstice before exposure to long days can again initiate seasonal quiescence.

Animals↗
PubMed1993

Diapause, pregnancy, and parturition in Australian marsupials.

Marsupial pregnancy is characterised by a long lactation and a relatively short gestation. Marsupials have, in effect, exchanged the umbilical cord for the teat. However, gestation can be extended for up to 11 months by the imposition of a period of developmental arrest known as embryonic diapause. Diapause may be under either lactational or seasonal control, and in the kangaroos and wallabies these effects are mediated by prolactin and melatonin, respectively. At the other end of gestation, namely parturition, it appears that marsupials are fairly typical mammals and require all the same physiological and behavioural cues essential for the delivery of a viable young. Parturition depends on a synchronised cascade of hormonal events triggered by the fetus itself. Prostaglandin and prolactin concentrations pulse around the time of birth and progesterone falls. Successful parturition also depends on the adoption of the appropriate behaviour and birth posture by the mother. Despite the fact that the entire period of gestation is accomplished in such a short time, the neonate has perfectly adapted its growth and development to influence its mother's physiology to induce the change from nurturing the young in its uterus via a placenta, to a precise synchronisation of the birth process resulting in completion of its growth within the pouch sustained by a milk tailor-made for each developmental stage.

Animals↗
PubMed1993

Monotreme development with particular reference to the extraembryonic membranes.

This paper considers many of the salient features of monotreme development, particularly morphogenesis of the extraembryonic membranes. The uterine endometrium of both monotremes and marsupials exhibits a progesterone driven luteal phase where accelerated utilization of endometrial nutrients is evidenced by a rapid post-primitive streak expansion in the dimensions of the extraembryonic membranes. Monotremes share with marsupials, birds, and reptiles an unspecialized vertebrate mode of genesis of the embryonic disc on the peripheral surface of the yolk-sac. The fused vascularized respiratory chorioallantois is estimated to have a functional life of not more than the terminal 4 to 5 days of the monotreme incubation period. This time interval is of a slightly greater order of magnitude than that found in marsupials with a fused chorioallantois, so far described, but in the context of the proportional elapse of post-primitive streak organogenesis would fall within the marsupial grade. The dominant extraembryonic membrane for nutritive and respiratory function in both monotremes and marsupials is the yolk-sac. This contribution shows that monotremes and marsupials share a much larger suite of developmental anatomical features than previously reported. The evolutionary biologist is confronted with the challenge of how to assign an appropriate weighting to these features as marsupials are considered by many researchers to be allied phylogenetically more closely with eutherian mammals than with monotremes.

Animals↗
PubMed1994

Origin of the oocyte shell membrane of a dasyurid marsupial: an immunohistochemical study.

Polyclonal antibodies were raised against the extracellular coats (mucoid and shell membrane) of unfertilized oocytes and early embryos of a dasyurid marsupial, the fat-tailed dunnart (Sminthopsis crassicaudata). Indirect immunofluorescence was used to test the specificity of the antibodies to the shell membrane. Streptavidin/biotin immunoperoxidase cytochemistry revealed that precursors of the tertiary egg membranes are secreted by the luminal epithelium of the ampulla, isthmus (including the crypts), utero-tubal junction, and adjacent endometrial glands. Histochemistry distinguished between the sites of mucoid and shell membrane precursor secretion. The mucoid coat stained positively with Alcian blue at pH 1.0 and 2.5, with Alcian blue at pH 0.2 after performic acid oxidation, and with PAS which was amylase resistant. Some of the luminal epithelial cells of the ampulla and isthmus, as well as its crypts, also stained positively by these histochemical methods but the luminal epithelium of the utero-tubal junction and endometrial glands were negative for all methods. The shell membrane did not stain with any of the above methods nor with dihydroxy-dinapthyl-disulphide (DDD) or ferric ferricyanide but it was eosinophilic and stained positively with the red cytoplasmic stain of Masson's trichrome. Therefore, it is concluded that shell membrane precursors are secreted by the luminal epithelium of the utero-tubal junction, adjacent glands, and by scattered glands in the anterior region of the uterus but not by any cell population of the oviduct.

Animals↗