Morphological Characterization of the Developing Greater Cane Rat (Thryonomys swinderianus) Brain.

Developmental mode along the altricial-precocial spectrum is well known to be influenced by brain development and maturation. The greater cane rat (GCR) is an indigenous precocial African rodent with uncommon phenotypes and life traits. This study was therefore designed to characterize and describe distinctive external developmental features in the prenatal GCR brain across the entire gestational length using the emergence and differentiation of external features of the brain vesicles. Four gross morphometric brain parameters (weight, length, width, and height) were evaluated and expressed as mean ± SEM. Relationship between all brain morphometrics and gestation length were analyzed using one-way ANOVA and linear regression. Developmental milestones in the prenatal GCR were then compared with closely related precocial mammals. The earliest time point with gross observable features in the prenatal GCR brain was at gestation day (GD) 60. The period with the most remarkable gross developmental features was noted between GD80 and GD100. Some of these gross features include differentiation of the cerebellar plate into vermis and lateral lobes, emergence of the piriform lobes, mammillary bodies, colliculi bodies, cerebral peduncles, and primordial pons. By GD130, most gross topographic neural features were already established. Cerebellar lobation and patterning at GD130 were the last recognizable gross developmental features noticed in the prenatal GCR brain. This coincided with the time of first eye opening in the GCR fetus. The developmental pattern observed in the prenatal GCR brain is similar to those noted in precocial rodent like the guinea pig. However, the onset of these milestones was delayed, and their duration was relatively shorter in the GCR. This study provides a frame of baseline reference of morphological brain features in the GCR embryos and fetuses that will be useful for fetal age estimation, for home grown neurodevelopmental and eco-toxicological studies, as this rodent is being proposed as a research model.

A Comparative Approach of Cellular Reprogramming in the Rodentia Order.

Cellular reprogramming mainly involves induction of reactivation of genes responsible for nuclear plasticity, a process that can be performed in vitro through production of cloned embryos by somatic cell nuclear transfer or by induction of cells into the pluripotent state through exogenous transcription factor expression. While these techniques are already well known and utilized in mice and rats, their application in other rodent species would be greatly beneficial, especially for conservation purposes. Within the diverse Rodentia order, wild species stand out as they play an important role in balancing the ecosystem by facilitating seed diversion, soil aeration, and consequently, reforestation. Many of these species are currently approaching extinction, and application of techniques, such as nuclear reprogramming, aimed at species conservation and multiplication and to produce stem cells is of interest. Thus, in this review, we aimed to present the evolution and success of nuclear reprogramming, mainly highlighting its potential application for the conservation of wild rodents.

Early and natural embryonic death in Lagostomus maximus: Association with the uterine glands, vasculature, and musculature.

The uterus is an organ with great plasticity due to the morphological and physiological changes it experiences during the estrous cycle and pregnancy. In mammals, pregnancy requires diverse sex hormones, growth factors and cytokines, among others, for promoting uterine remodeling to favor implantation, placentation, and embryo/fetus survival and growth. The hystricognathi rodent Lagostomus maximus (plains viscacha) has a high rate of embryonic resorption. The cranial and middle implants are reabsorbed 25-35 days after intercourse while the caudal embryos continue with their development until two precocial offspring are born. So far, no uterine studies of non-pregnant L. maximus females were performed to determine the possible existence of variations in the organ that could be related to the differential survival of the implants. We used ultrasonography, as well as morphological, morphometric, histochemical, lectinhistochemical, and immunohistochemical methods to study differences in the uterine glands (area), vasculature (area), and musculature (thickness) along the uterine horns in non-pregnant females. Along the uterus, all these structures were in more advanced developmental condition in the caudal region as compared to more anterior positions. These regional variations could be decisive in explaining the reason why only caudal implantations come to term. In contrast, no differences in the in the luminal and glandular epithelial cells, nor in the degree of cell proliferation and apoptosis, and hormonal receptor staining were found. These parameters could be related to implantation along the uterine horns, but not to the differential survival of the implants.

Developmental horizons in the pre-natal development of the Greater cane rat (Thryonomys swinderianus).

The Greater cane rat (GCR, Thyronomys swinderianus) is a precocial rodent predominantly found within Africa. Economic and scientific interests have led to several research efforts towards the domestication and better understanding of the biology and development of this rodent. Despite these efforts, information on the pre-natal development of this rodent is currently lacking. This study characterises distinct developmental milestones including skin pigmentation, emergence and distributions of hairs, calvarium consistency, teeth eruption, development of appendages, sensory organs and external genitalia in the pre-natal GCR and assesses quantitative body parameters, that is body weight, body and crown-rump lengths across its entire gestation length (gestation days [GDs] 10-140). Using these external features, we provide baseline reference ontogenetic scales for GCR embryos and fetuses, employable for stage, age and sex estimation of the pre-natal GCR in future studies. We observed that the first evidence of an embryo was not seen before the end of the first trimester (GD50) and that the late second trimester (GD80-GD100) marks the transition from embryogenesis to fetogenesis in the GCR. As both events occur at a much later developmental time point when compared to precocial non-rodents including human, sheep and pig and slightly later when compared to other precocial rodents such as guinea pig, our data provide first indication that the pre-natal GCR development might be associated with a reproductive delay. Together, this study expands our knowledge of the development and biology of the GCR, which will improve reproductive and breeding management, and native species conservation of this hystricomorph mammal.

Diverse developmental strategies of X chromosome dosage compensation in eutherian mammals.

In eutherian mammals, dosage compensation arose to balance X-linked gene expression between sexes and relatively to autosomal gene expression in the evolution of sex chromosomes. Dosage compensation occurs in early mammalian development and comprises X chromosome upregulation and inactivation that are tightly coordinated epigenetic processes. Despite a uniform principle of dosage compensation, mechanisms of X chromosome inactivation and upregulation demonstrate a significant variability depending on sex, developmental stage, cell type, individual, and mammalian species. The review focuses on relationships between X chromosome inactivation and upregulation in mammalian early development.

Periodic patterns in Rodentia: Development and evolution.

Mammalian periodic pigment patterns, such as spots and stripes, have long interested mathematicians and biologists because they arise from non-random developmental processes that are programmed to be spatially constrained, and can therefore be used as a model to understand how organized morphological structures develop. Despite such interest, the developmental and molecular processes underlying their formation remain poorly understood. Here, we argue that Arvicanthines, a clade of African rodents that naturally evolved a remarkable array of coat patterns, represent a tractable model system in which to dissect the mechanistic basis of pigment pattern formation. Indeed, we review recent insights into the process of stripe formation that were obtained using an Arvicanthine species, the African striped mouse (Rhabdomys pumilio), and discuss how these rodents can be used to probe deeply into our understanding of the factors that specify and implement positional information in the skin. By combining naturally evolved pigment pattern variation in rodents with classic and novel experimental approaches, we can substantially advance our understanding of the processes by which spatial patterns of cell differentiation are established during embryogenesis, a fundamental question in developmental biology.

Imunolocalização de receptores de leptina no ovário de preás (Galea spixii Wagler, 1831) / Immunolocalization of leptin receptor of Spix's Yellow-toothed Cavy (Galea spixii Wagler, 1831) ovary

A leptina, uma citocina produzida pelas células adiposas, é alvo da comunidade científica por acreditarem que ela apresente impacto sobre a reprodução dos animais promovendo a puberdade, foliculogênese e oogênese, ciclo estral e auxiliando na fecundação. A compreensão dos mecanismos que controlam a atividade reprodutiva de preás (Galea spixii) possui papel relevante para a preservação da espécie. Desta forma, o presente trabalho propôs analisar a imunolocalização dos receptores de leptina (Ob-R) no ovário de preás. Coletaram-se os ovários de 20 fêmeas adultas, não prenhes e saudáveis. As amostras foram fixadas em paraformaldeído a 4% em tampão fosfato, incluídas em parafina e seccionadas para a realização de imunohistoquímica (IHC). As secções foram fotomicrografadas e avaliadas quanto à intensidade da reação. Observou-se forte imunorreação no oócito e nas células da teca, moderada nas células do estroma ovariano e nas células luteínicas grandes e fracamente coradas nas células da granulosa, endoteliais, perivasculares e células luteínicas pequenas. Quando comparado a expressão de receptores ao longo do desenvolvimento folicular foi observado que o oócito e as células da teca se mantiveram com expressão na mesma intensidade. Entretanto, as células da granulosa apresentaram forte marcação nos estádios pré-antrais enquanto que nos folículos antrais apresentou fraca intensidade. Concluímos que em ovários de Galea spixii existe a presença de Ob-R nas principais estruturas do ovário sugerindo que este hormônio desempenhe papel fundamental na reprodução desta espécie.

Leptin, a cytokine produced by adipose cells, is the target of the scientific community for believing that it has an impact on the reproduction of the animals promoting puberty, folliculogenesis and oogenesis, estrous cycle and aiding in fertilization. The understanding of the mechanisms controlling the reproductive activity of Spix's Yellow-toothed Cavy (Galea spixii) plays a relevant role in the preservation of the species. Thus, the present study proposed to analyze the immunolocalization of leptin receptors (Ob-R) in the ovary of cavies. Ovaries from 20 adult, non-pregnant, healthy females were collected. The samples were fixed in 4% phosphate buffered paraformaldehyde, embedded in paraffin and sectioned for immunohistochemistry. The sections were photomicrographs and intensity of the reaction was measured. Strong immunoreaction was observed in oocyte and theca cells, moderate in ovarian stromal cells and large luteal cells and weak stained in granulosa, endothelial, perivascular and small luteal cells. When compared to receptor expression along follicular development it was observed that the oocyte and the theca cells remained with expression at the same intensity. However, the granulosa cells presented strong stained in the preantral stages, whereas in the antral follicles it presented low intensity. We conclude that in the ovaries of Galea spixii there is the presence of Ob-R in the main structures of the ovary sugesting that this hormone plays a fundamental role in the reproduction of this species.

Cell migration in the developing rodent olfactory system.

The components of the nervous system are assembled in development by the process of cell migration. Although the principles of cell migration are conserved throughout the brain, different subsystems may predominantly utilize specific migratory mechanisms, or may display unusual features during migration. Examining these subsystems offers not only the potential for insights into the development of the system, but may also help in understanding disorders arising from aberrant cell migration. The olfactory system is an ancient sensory circuit that is essential for the survival and reproduction of a species. The organization of this circuit displays many evolutionarily conserved features in vertebrates, including molecular mechanisms and complex migratory pathways. In this review, we describe the elaborate migrations that populate each component of the olfactory system in rodents and compare them with those described in the well-studied neocortex. Understanding how the components of the olfactory system are assembled will not only shed light on the etiology of olfactory and sexual disorders, but will also offer insights into how conserved migratory mechanisms may have shaped the evolution of the brain.

Assessment of sex specific endocrine disrupting effects in the prenatal and pre-pubertal rodent brain.

BACKGROUND: Brain sex differences are found in nearly every region of the brain and fundamental to sexually dimorphic behaviors as well as disorders of the brain and behavior. These differences are organized during gestation and early adolescence and detectable prior to puberty. Endocrine disrupting compounds (EDCs) interfere with hormone action and are thus prenatal exposure is hypothesized to disrupt the formation of sex differences, and contribute to the increased prevalence of pediatric neuropsychiatric disorders that present with a sex bias. OBJECTIVE: Available evidence for the ability of EDCs to impact the emergence of brain sex differences in the rodent brain was reviewed here, with a focus on effects detected at or before puberty. METHODS: The peer-reviewed literature was searched using PubMed, and all relevant papers published by January 31, 2015 were incorporated. Endpoints of interest included molecular cellular and neuroanatomical effects. Studies on behavioral endpoints were not included because numerous reviews of that literature are available. RESULTS: The hypothalamus was found to be particularly affected by estrogenic EDCs in a sex, time, and exposure dependent manner. The hippocampus also appears vulnerable to endocrine disruption by BPA and PCBs although there is little evidence from the pre-pubertal literature to make any conclusions about sex-specific effects. Gestational EDC exposure can alter fetal neurogenesis and gene expression throughout the brain including the cortex and cerebellum. The available literature primarily focuses on a few, well characterized EDCs, but little data is available for emerging contaminants. CONCLUSION: The developmental EDC exposure literature demonstrates evidence of altered neurodevelopment as early as fetal life, with sex specific effects observed throughout the brain even before puberty.

Patterning and post-patterning modes of evolutionary digit loss in mammals.

A reduction in the number of digits has evolved many times in tetrapods, particularly in cursorial mammals that travel over deserts and plains, yet the underlying developmental mechanisms have remained elusive. Here we show that digit loss can occur both during early limb patterning and at later post-patterning stages of chondrogenesis. In the 'odd-toed' jerboa (Dipus sagitta) and horse and the 'even-toed' camel, extensive cell death sculpts the tissue around the remaining toes. In contrast, digit loss in the pig is orchestrated by earlier limb patterning mechanisms including downregulation of Ptch1 expression but no increase in cell death. Together these data demonstrate remarkable plasticity in the mechanisms of vertebrate limb evolution and shed light on the complexity of morphological convergence, particularly within the artiodactyl lineage.

Prenatal development of the agouti (Dasyprocta prymnolopha Wagler, 1831): External features and growth curves.

The gestation period in agoutis can range from 104 to 120 days. Knowledge regarding the morphological characteristics of embryos and fetuses is important as a base for studies in reproduction biotechnology, such as in vitro fertilization, embryo transfer and helps in determining congenital anomalies during the development phase. Thus, given the importance and lack of information about agouti embryology, the objective of this study was to characterize the external morphology and define the biometry of embryos and fetuses, at different days of development. Nine females were submitted to daily colpocytology to identify the estrus, confirm mating and identify day zero of the gestation. When the mating was confirmed they were weighed, underwent abdominal ultrasonography and surgery was conducted on the females at the gestational ages of 25, 30, 35, 40, 45, 50, 75 and 100 days. Sixteen embryos/fetuses were weighed and measured. Agouti embryos at 25 days after mating are "C" shaped, with primitive structures, 0.4±0.01cm crown-rump and weighed 0.06±0.01g; at 30 days after mating the crown-rump was 0.95±0.07cm and weighed 0.28±0.00g; at 35 days after mating the crown-rump was 155±0.07cm and weighed 0.38±0.01g; at 40 days after mating the crown-rump was 2.25±0.21cm and weighed 1.25±0.07g; at 45 days after mating the crown-rump was 3.45±0.35cm and weighed 2.75±0.64g; at 50 days after mating the crown-rump was 5.0±0.3cm and weighed 7.01±2.6g; at 75 days after mating, the skin was dark, the crown-rump was 10.0±0.14cm and weighed 55.2±0.07g. At 100 days after mating, the crown-rump was 13.8±0.49cm and fetuses weighed 136.7±9.40g. Based on the morphological data assessed the embryo and fetus age could be assessed and the size and average weight of agouti embryos was established.

Microscopy of the umbilical cord of rock cavies--Kerodon rupestris Wied, 1820 (Rodenta, Caviidae).

The rock cavies (Kerodon rupestris) are rodents belonging to family Caviidae, with habitat restricted to northeastern Brazil. Current studies have shown that blood cord has stem and hematopoietic cells both with a high regenerative potential, microscopic studies about the description in rodents and other mammals are scarce. The aim of this study was to describe the structural components of the umbilical cord of rock cavies. Rock cavies embryos at different stages of pregnancy were used, three in the first third, five in middle third, and six in the final third of gestation. They were obtained at the Centre for Wild Animals Multiplication of Federal Rural University of Semi-Arid. In rock cavies was observed that the number of vessels involved in the transport of maternal substances was represented by two major arteries, veins and an allantois duct. The umbilical cord was delimited by amniotic epithelium, formed by a layer of squamous cells, connective tissue with characteristic of the mucosal tissue, corresponding to the Wharton jelly (fetal mesenchyme), where elastic fibers were observed and intercellular spaces were arranged in concentric blades. The morphology observed in rock cavies is similar to that described in the literature for other mammals, including man. The rock cavies are well adapted to captivity and are docile, which makes this animal an important model for study within the field of regenerative medicine. The knowledge of the umbilical cord morphology represents a base point for using this animal as a model for culture and cell therapy.

Predicting the energy and protein requirements of the pregnant grasscutter (Thryonomys swinderianus, Temminck) using the changes in weight and composition of the foetus and associated tissues of pregnancy.

Eighteen (18) gravid uteri collected from hunters' kills during February and March 2008 were used to investigate growth and accretion of energy and protein in the gravid uterus during pregnancy in the grasscutter. Each gravid uterus was separated into foetal, placental, empty uterus and foetal fluids (amniotic and allantoic fluids combined) components. Individual tissues were weighed and analyzed for dry matter (DM), ash, crude protein (CP) and crude fat. Regression equations were fitted to the weights of each component to describe the effects of gestational age. The DM, protein and energy contents of individual uterine tissues, with the exception of the DM of the foetal fluids, increased significantly with advancing gestation age so that the DM of the gravid uterus increased ~20-fold from days 45 to 152 (3.85 v. 76.24 g). However, the average elemental N in the foetus was 8.3 g N/100 g. Percentage DM did not change with advancing gestation age. Fat content of the foetal grasscutter was 2.79 %. Changes in foetal protein and energy fitted a multi-phasic regression that consisted of two linear equations. Similarly, changes in foetal fat and water contents fitted a multi-phasic regression that consisted of two linear equations, indicating that protein and energy growth accelerated after days 95 and 97 of gestation, respectively, with increases in fat and water accelerating after days 127 and 96 of gestation, respectively. Foetal protein and energy accretions were 0.04 g day(-1) and 0.001 MJ day(-1) before days 95 and 97 of gestation, respectively, and increased to 0.31 g day(-1) and 0.009 MJ day(-1) after days 95 and 97 of gestation, respectively. Fat and water accretions were also 0.012 g day(-1) and 0.15 ml day(-1) before days 127 and 96 of gestation, respectively, and increased to 0.104 g day(-1) and 1.29 ml day(-1) after the respective days of gestation. Protein needs for tissue protein gain increased ~8-fold after day 95 of gestation. Results of this study indicate that the growth of the foetus and foetal tissues occur at different rates during gestation and points to a two-phase feeding strategy before and after day 95 of gestation for pregnant grasscutters.

Pregnancy in Hystricomorpha: gestational age and embryonic-fetal development of agouti (Dasyprocta prymnolopha, Wagler 1831) estimated by ultrasonography.

Thirty-one pregnant agoutis, between Days 9 and 103 of gestation (Day 1 = day of detection of sperm in the vaginal smear), underwent B-mode ultrasonography; gestational sac diameter (GSD), crown-rump length (CRL), embryonic-fetal diameter (EFD), and placenta diameter (PD) were measured. There were positive correlations (P < 0.05) between GSD and CRL (r = 0.98), GSD and PD (r = 0.88), CRL and PD (r = 0.86), days of gestation (DG) and CRL (r = 0.85), and DG and PD (r = 0.73). The gestational sac was first observed on Day 14. The embryo was first seen on Day 18 in 9/31 of pregnant agoutis and on Day 22 in 20/31 of pregnant agoutis. Heartbeats were detected from the Day 25 and placentas were observed in 100% of the animals from Day 25. Early limb bud and ossification of the fetal skull were identified on Days 27 (15/31) and 45 (24/31), respectively. Fetal orientation (head and body) was evident from Day 40, the stomach, liver and lungs were identified on Day 50, the kidneys were reliably seen only on Day 55, and the aorta and vena cava were seen on Day 70. The fetal bowel and the urinary bladder were the last structures to be observed (Day 85). Ultrasonography was effective for early pregnancy diagnosis in agouti and for obtaining information on embryonic and fetal structures that could be used to predict gestational age and birth, thereby contributing to their reproductive management in captivity.

Germ cell differentiation and proliferation in the developing testis of the South American plains viscacha, Lagostomus maximus (Mammalia, Rodentia).

Cell proliferation and cell death are essential processes in the physiology of the developing testis that strongly influence the normal adult spermatogenesis. We analysed in this study the morphometry, the expression of the proliferation cell nuclear antigen (PCNA), cell pluripotency marker OCT-4, germ cell marker VASA and apoptosis in the developing testes of Lagostomus maximus, a rodent in which female germ line develops through abolished apoptosis and unrestricted proliferation. Morphometry revealed an increment in the size of the seminiferous cords with increasing developmental age, arising from a significant increase of PCNA-positive germ cells and a stable proportion of PCNA-positive Sertoli cells. VASA showed a widespread cytoplasmic distribution in a great proportion of proliferating gonocytes that increased significantly at late development. In the somatic compartment, Leydig cells increased at mid-development, whereas peritubular cells showed a stable rate of proliferation. In contrast to other mammals, OCT-4 positive gonocytes increased throughout development reaching 90% of germ cells in late-developing testis, associated with a conspicuous increase in circulating FSH from mid- to late-gestation. TUNEL analysis was remarkable negative, and only a few positive cells were detected in the somatic compartment. These results show that the South American plains viscacha displays a distinctive pattern of testis development characterized by a sustained proliferation of germ cells throughout development, with no signs of apoptosis cell demise, in a peculiar endocrine in utero ambiance that seems to promote the increase of spermatogonial number as a primary direct effect of FSH.

Os histricomorfos sul-americanos: uma análise comparativa do desenvolvimento embriológico / South-American hystricomorphs: a comparative analysis of embryological development

O objetivo do estudo foi realizar uma análise embriológica dos roedores histricomorfos (paca, cutia, preá e capivara), a fim de comparar com a de outros roedores e com a morfogênese humana um padrão embriológico. Utilizaram-se 8 espécimes de roedores sendo, 2 embriões para cada espécie coletada, ambas em inicio de gestação. Estes foram retirados dos úteros gestantes através de ovariosalpingohisterectomia parcial, seguido de fixação em solução de paraformaldeído 4 por cento. Para as mensurações de Crow-Rump, adotou-se como referência a crista nucal numa extremidade e da última vértebra sacral na extremidade oposta. De forma geral, os embriões analisados mostraram as seguintes características morfológicas: divisão dos arcos branquiais, o não fechamento do neuróporo cranial em alguns embriões estudados, a curvatura cranial acentuada e os somitos delimitados e individualizados. O broto dos membros apresentava-se em desenvolvimento em formato de remo, além da impressão cardíaca e fígado. Na região caudal, visualizou-se a curvatura crânio-caudal, a vesícula óptica com e sem pigmentação da retina, a abertura do tubo neural na região do quarto ventrículo encefálico, a fosseta nasal e a formação das vesículas encefálicas. Concluímos que desenvolvimento embriológico dos roedores histricomorfos pode ser comparado à morfogênese de ratos, cobaios, coelhos e humanos nos diferentes estágios de desenvolvimento, tomando apenas o cuidado com as particularidades de cada espécie, além da implementação de tecnologias reprodutivas, especialmente a de embriões, a qual requer o conhecimento do desenvolvimento pré-implantação referente às fases de desenvolvimento.

The aim of this study was to perform an embryology analysis of South-American hystricomorph rodents (paca, agouti, capybara, and rock cavy) to compare these data with the ones from other rodents and with the human embryologic morphogenesis. We used 8 samples of rodents, 2 embryos for each species, collected during early gestation. The embryos were removed from the pregnant uterus through partial ovarysalpingohysterectomy, followed by fixation in 4 percent paraformaldehyde solution. For crow-rump measurements, we had as reference the nuchal crest at one extremity and the last sacral vertebra on the opposite side. The embryos examined showed the following morphological characteristics: Division of the branchial arches, the cranial neuropore open in some embryos studied, the cranial curvature developed, and the somites delimited and distinct. The hindlimb and forelimb were in development, and showed "row" form; so we found the cardiac impression and the liver region. In the caudal region we observed the head-flow curve, the optic vesicle with and without pigmentation of the retina, the opening of neural tube in the fourth ventricle region of the brain, the nasal cavity, and the encephalic vesicles formation. We conclude that the embryo development of hystricomorph rodents can be compared with the morphogenesis in rats, guinea pigs, rabbits and humans in the early stages of development, being aware of the particularities for each species, in addition to the implementation of reproductive technology, especially of embryos, what requires knowledge of the pre-implantation stages for the different development phases.

The developing ovary of the South American plains vizcacha, Lagostomus maximus (Mammalia, Rodentia): massive proliferation with no sign of apoptosis-mediated germ cell attrition.

Apoptosis-dependent massive germ cell death is considered a constitutive trait of the developing mammalian ovary that eliminates 65-85% of the germinal tissue depending on the species. After birth and during adult lifetime, apoptotic activity moves from the germ cell proper to the somatic compartment, decimating germ cells through follicular atresia until the oocyte reserve is exhausted. In contrast, the South American rodent Lagostomus maximus shows suppressed apoptosis-dependent follicular atresia in the adult ovary, with continuous folliculogenesis and massive polyovulation, which finally exhausts the oocyte pool. The absence of follicular atresia in adult L. maximus might arise from a failure to move apoptosis from the germinal stratum to the somatic compartment after birth or being a constitutive trait of the ovarian tissue with no massive germ cell degeneration in the developing ovary. We tested these possibilities by analysing oogenesis, expression of germ cell-specific VASA protein, apoptotic proteins BCL2 and BAX, and DNA fragmentation by TUNEL assay in the developing ovary of L. maximus. Immunolabelling for VASA revealed a massive and widespread colonisation of the ovary and proliferation of germ cells organised in nests that disappeared at late development when folliculogenesis began. No sign of germ cell attrition was found at any time point. BCL2 remained positive throughout oogenesis, whereas BAX was slightly detected in early development. TUNEL assay was conspicuously negative throughout the development. These results advocate for an unrestricted proliferation of germ cells, without apoptosis-driven elimination, as a constitutive trait of L. maximus ovary as opposed to what is normally found in the developing mammalian ovary.

Review: Genetic manipulation of the rodent placenta.

The principal role of the placenta is the maintenance of pregnancy and promotion of fetal growth and viability. The use of transgenic rodents has greatly enhanced our understanding of placental development and function. However, embryonic lethality is often a confounding variable in determining whether a genetic modification adversely affected placental development. In these cases, it is beneficial to specifically manipulate the placental genome. The purpose of this review is to summarize available methodologies for specific genetic modification of the rodent placenta. By restricting genetic alterations to the trophoblast lineage, it is possible to gain a deeper understanding of placental development that perhaps will lead to gene-targeted therapies to rescue irregular placentation in transgenic animals or in women at high-risk for placenta-associated pregnancy complications.

Thomas George Lee - Implantation and early development of North American rodents.

A century ago Thomas G. Lee amassed an unparalleled collection of developmental series of North American rodents such as the thirteen-lined ground squirrel, the Plains pocket gopher and Merriam's kangaroo rat. He was the first to describe the initial attachment of the squirrel blastocyst to the antimesometrial side of the uterus. The full potential of Lee's material was not realized until after his death, when it came into the possession of Mossman. The latter relied heavily on Lee's collection when writing his seminal monograph on the comparative morphogenesis of fetal membranes and much of Lee's material was subsequently described in detail by Mossman and others. It now forms part of the Harland W. Mossman Collection at the University of Wisconsin.

In utero and exo utero surgery on rodent embryos.

Mammalian development has been best characterized using the mouse model. Direct intervention of the postimplantation mouse embryo in utero represents one of many experimental approaches that can be used to probe mammalian embryogenesis. Experimental access to the mouse embryo is difficult, but techniques have been developed to circumvent some of the challenges of operating on the embryo in vivo. Experimental studies have been carried out on postimplantation stage embryos from E8.5 to term, so much of the gestational period is accessible for experimentation. One approach that has helped to enhance embryo accessibility was the development of surgical techniques based on the finding that embryonic development continued normally exo utero. Exo utero development refers to the surgically created condition in which the embryo develops outside of the uterine cavity, yet within the female abdominal cavity and attached, via the placenta, to the uterus. Using this approach it is feasible to carry out precise surgical manipulations of the mouse embryo without compromising embryo viability associated with postsurgery uterine contractions. In this chapter we review technical aspects of both in utero and exo utero surgical approaches and how these surgeries are used in conjunction with other experimental applications.