Acute multiple organ failure in adult mice deleted for the developmental regulator Wt1

There is much interest in the mechanisms that regulate adult tissue homeostasis and their relationship to processes governing foetal development. Mice deleted for the Wilms' tumour gene, Wt1, lack kidneys, gonads, and spleen and die at mid-gestation due to defective coronary vasculature. Wt1 is vital for maintaining the mesenchymal–epithelial balance in these tissues and is required for the epithelial-to-mesenchyme transition (EMT) that generates coronary vascular progenitors. Although Wt1 is only expressed in rare cell populations in adults including glomerular podocytes, 1% of bone marrow cells, and mesothelium, we hypothesised that this might be important for homeostasis of adult tissues; hence, we deleted the gene ubiquitously in young and adult mice. Within just a few days, the mice suffered glomerulosclerosis, atrophy of the exocrine pancreas and spleen, severe reduction in bone and fat, and failure of erythropoiesis. FACS and culture experiments showed that Wt1 has an intrinsic role in both haematopoietic and mesenchymal stem cell lineages and suggest that defects within these contribute to the phenotypes we observe. We propose that glomerulosclerosis arises in part through down regulation of nephrin, a known Wt1 target gene. Protein profiling in mutant serum showed that there was no systemic inflammatory or nutritional response in the mutant mice. However, there was a dramatic reduction in circulating IGF-1 levels, which is likely to contribute to the bone and fat phenotypes. The reduction of IGF-1 did not result from a decrease in circulating GH, and there is no apparent pathology of the pituitary and adrenal glands. These findings 1) suggest that Wt1 is a major regulator of the homeostasis of some adult tissues, through both local and systemic actions; 2) highlight the differences between foetal and adult tissue regulation; 3) point to the importance of adult mesenchyme in tissue turnover.

It is important to understand the cellular and molecular pathways that regulate the maintenance and turnover of adult tissues. These processes often go awry in diseases and are likely to deteriorate with ageing. Here we show that removal of a single gene, the Wilms' Tumour gene, Wt1, in the adult mouse leads to the extremely rapid deterioration of multiple tissues. Within 7–9 days after gene removal kidneys fail, the pancreas and spleen suffer severe atrophy, there is widespread loss of bone and body fat, and red blood cells are no longer produced. Our findings reveal the vulnerability of adult tissues, while opening up avenues for dissecting the pathways controlling tissue turnover. Further experiments showed that the tissue failure we observed is due both to local defects of stem/progenitor cell activities and to significant changes in the serum levels of some key master regulators. In particular there is a dramatic reduction in the levels of IGF-1, a key regulator of homeostasis and aging. Our studies also show that the control of adult tissue turnover may be different from that during foetal development. These findings have important implications for understanding and treating common human diseases.

A genetic screen for mutations affecting gonad formation in Drosophila reveals a role for the slit/robo pathway

Organogenesis is a complex process requiring multiple cell types to associate with one another through correct cell contacts and in the correct location to achieve proper organ morphology and function. To better understand the mechanisms underlying gonad formation, we performed a mutagenesis screen in Drosophila and identified twenty-four genes required for gonadogenesis. These genes affect all different aspects of gonad formation and provide a framework for understanding the molecular mechanisms that control these processes. We find that gonad formation is regulated by multiple, independent pathways; some of these regulate the key cell adhesion molecule DE-cadherin, while others act through distinct mechanisms. In addition, we discover that the Slit/Roundabout pathway, best known for its role in regulating axonal guidance, is essential for proper gonad formation. Our findings shed light on the complexities of gonadogenesis and the genetic regulation required for proper organ formation.

Normal male sexual differentiation and aetiology of disorders of sex development

Fetal sex development consists of three sequential stages: a) the undifferentiated stage, when identical primitive structures develop in the XY and XX embryos, b) gonadal differentiation into testes or ovaries, and c) the differentiation of internal and external genitalia, which depends on the action of testicular hormones. Disorders of sex development (DSD) may result from defects in any of these stages. Abnormal formation of the anlagen of internal and/or external genitalia in early embryonic development results in Malformative DSD. In patients with a Y chromosome, defects in testis differentiation drive to early-onset fetal hypogonadism affecting whole testicular function, a condition named Dysgenetic DSD. In Non-dysgenetic DSD, the underlying pathogenesis may involve early-onset fetal hypogonadism affecting specifically either Leydig or Sertoli cell function, or male hormone end-organ defects in patients devoid of fetal hypogonadism. Understanding the pathogenesis is useful for an efficient early diagnosis approach, which is necessary for adequate decision making in the management of DSD.

Copy number variation in patients with disorders of sex development due to 46,XY gonadal dysgenesis

Disorders of sex development (DSD), ranging in severity from mild genital abnormalities to complete sex reversal, represent a major concern for patients and their families. DSD are often due to disruption of the genetic programs that regulate gonad development. Although some genes have been identified in these developmental pathways, the causative mutations have not been identified in more than 50% 46,XY DSD cases. We used the Affymetrix Genome-Wide Human SNP Array 6.0 to analyse copy number variation in 23 individuals with unexplained 46,XY DSD due to gonadal dysgenesis (GD). Here we describe three discrete changes in copy number that are the likely cause of the GD. Firstly, we identified a large duplication on the X chromosome that included DAX1 (NR0B1). Secondly, we identified a rearrangement that appears to affect a novel gonad-specific regulatory region in a known testis gene, SOX9. Surprisingly this patient lacked any signs of campomelic dysplasia, suggesting that the deletion affected expression of SOX9 only in the gonad. Functional analysis of potential SRY binding sites within this deleted region identified five putative enhancers, suggesting that sequences additional to the known SRY-binding TES enhancer influence human testis-specific SOX9 expression. Thirdly, we identified a small deletion immediately downstream of GATA4, supporting a role for GATA4 in gonad development in humans. These CNV analyses give new insights into the pathways involved in human gonad development and dysfunction, and suggest that rearrangements of non-coding sequences disturbing gene regulation may account for significant proportion of DSD cases.

Two regions within the proximal steroidogenic factor 1 promoter drive somatic cell-specific activity in developing gonads of the female mouse

Targets of steroidogenic factor 1 (SF1; also known as NR5A1 and AD4BP) have been identified within cells at every level of the hypothalamic-pituitary-gonadal and -adrenal axes, revealing SF1 to be a master regulator of major endocrine systems. Mouse embryos express SF1 in the genital ridge until Embryonic Day 13.5 (E13.5). Thereafter, expression persists in the male and is substantially lower in the female gonad until birth. We hypothesize that the sexually dimorphic expression of Sf1 during gonadogenesis is mediated by sex-specific regulation of its promoter. To investigate dimorphic regulation within the fetal gonad, we developed an experimental strategy using transient transfection of E13.5 gonad explant cultures and evaluated various Sf1 promoter constructs for sexually dimorphic DNA elements. The proximal Sf1 promoter correctly targeted reporter activity to SF1-expressing cells in both XY and XX gonads. Stepwise deletion of sequences from the Sf1 promoter revealed two regions that affected regulation within female gonads. Mutation of both sequences together did not cause further disruption of reporter activity, suggesting the two sites might work in concert to promote activity in female somatic cells. Results from gel mobility shift assays and fetal gonad-chromatin immunoprecipitation showed that TCFAP2 binds to one of the two female-specific sites within the proximal promoter of Sf1. Together, we show that transient transfection experiments performed within developing testes and ovaries are a powerful tool to uncover elements within the Sf1 promoter that contribute to sex-specific expression.

Expression of PITX2 homeodomain transcription factor during rat gonadal development in a sexually dimorphic manner

PITX2, a multifunctional Paired-like homeodomain transcription factor, plays obligatory role during development of organs like heart, brain and pituitary. It regulates differentiation of vascular smooth muscle cells and hematopoietic stem cells. Although we earlier reported the Pitx2/PITX2 expression in gonad, but the expression pattern of its different isoforms in mammalian gonads especially during development is still not known. As PITX2 participates in the development of multiple organs and different homeobox genes have been shown to control gonadal functions, we wanted to investigate the role of PITX2 in gonadal development and its function. The objective of our study was to know the expression profile of different Pitx2/PITX2 isoforms and its localization throughout the development of gonads. Here we show the temporal and spatial expression pattern of Pitx2/PITX2 and its localization throughout the embryonic and postnatal stages of rat gonads. Pitx2/PITX2 expression profile reveals the differential and dimorphic expression pattern of its two isoforms PITX2B2 and-Cβ throughout the embryonic development stages and also in the postnatal stages, where it becomes more prominent. This is the first report where PITX2 homeodomain transcription factor shows isoform-specific sexually dimorphic expression. In addition, PITX2 localization was found in the embryonic ovarian primordial germ cell clusters and germ cells inside the testicular cords and also in somatic cells. In adults, ovarian granulosa and theca cells as well as germ cells inside the seminiferous tubules in testis express PITX2. All the evidences suggest that the differential expression of PITX2 might be associated with sex-specific embryonic and postnatal gonadal development and the physiological processes.

Differential expression of three estrogen receptor subtype mRNAs in gonads and liver from embryos to adults of the medaka, Oryzias latipes

In fish, estradiol-17β (E2) regulates various reproductive processes by acting through estrogen receptors (ERs). Here, we cloned three ER subtypes from medaka and examined their developmental expression in the gonads and liver of genetically females and males from embryos to adults. During embryogenesis, marked increases in the expression of ERβ2, but not either ERα or ERβ1, were found in genetically female embryos during sex differentiation. E2 treatment induced marked up-regulation of ERβ2 expression in genetically male embryos. In adult ovaries, ERα levels were high in follicles (granulosa cells) during oocyte growth. In the testis, ERβ1 expression exhibited a distinct peak at 10 days post hatching (dph). In the liver, very high levels of ERβ2 were found in both females and males throughout the sampling period with significantly higher levels in females during 30-50 dph. These findings suggest each action of E2 to be mediated by different types of ERs.

Expression of miRNAs in ovine fetal gonads: potential role in gonadal differentiation

BACKGROUND

Gonadal differentiation in the mammalian fetus involves a complex dose-dependent genetic network. Initiation and progression of fetal ovarian and testicular pathways are accompanied by dynamic expression patterns of thousands of genes. We postulate these expression patterns are regulated by small non-coding RNAs called microRNAs (miRNAs). The aim of this study was to identify the expression of miRNAs in mammalian fetal gonads using sheep as a model.

METHODS

We determined the expression of 128 miRNAs by real time PCR in early-gestational (gestational day (GD) 42) and mid-gestational (GD75) sheep ovaries and testes. Expression data were further examined and validated by bioinformatic analysis.

RESULTS

Expression analysis revealed significant differences between ovaries and testes among 24 miRNAs at GD42, and 43 miRNAs at GD75. Bioinformatic analysis revealed that a number of differentially expressed miRNAs are predicted to target genes known to be important in mammalian gonadal development, including ESR1, CYP19A1, and SOX9. In situ hybridization revealed miR-22 localization within fetal testicular cords. As estrogen signaling is important in human and sheep ovarian development, these data indicate that miR-22 is involved in repressing estrogen signaling within fetal testes.

CONCLUSIONS

Based on our results we postulate that gene expression networks underlying fetal gonadal development are regulated by miRNAs.

Imaging pluripotent cell migration in Drosophila

Drosophila melanogaster offers a powerful system for the analysis of cell migration. In the embryo, -pluripotent cells of the mesodermal and endodermal primordia undergo epithelial-mesenchymal transitions and cell migration, while primordial germ cells migrate through an endodermal barrier to form the gonads. Visualisation of these migrations has traditionally been achieved by staining fixed embryos at different developmental stages or through live imaging of cells using tissue-specific expression of marker fluorescent proteins. More recently, photoactivatable fluorescence proteins have allowed the labelling of small groups of cells or single cells so that their migratory patterns and fate can be followed. By fusing the photoactivatable fluorescent protein to proteins that mark different subcellular components, it is now possible to visualise different aspects of the cells as they migrate. Here, we review previous studies of the migration of pluripotent embryonic cells and describe, in detail, methods for visualising these cells.

[The mammalian gonocytes fate: oogenesis or spermatogenesis]

Germ line cells become gonocytes after the completion of migration and colonization of gonadal anlages. After the contact with the somatic cells of genital ridges the reprogramming of gonocytes takes place. Upon entry the embryonic gonads germ cells undergo the most complete demethylation during germ line development, their chromatin tends to have an open conformation for a short period. This event promotes the susceptibility to meiosis-inducing factors signaling. The choice of the further path of gonocytes development just after the gonadal sex differentiation, mitotic arrest and meiotic entry are discussed. Analisis of the action mechanisms of meiosis-inducing and meiosis-preventing factors, especially retinoic acid and enzymes of its degradation and synthesis, was performed.

[The mammalian and the human primary germ cells. Differentiation, identification, migration]

Last years' many new facts on gene expression at the different stages of PGC development were obtained. The process of germline segregation in different species realizes in different manner--as preformation or epigenesis. In the review the mechanisms of the mammalian and the human initial germ cell lineage specification are dicussed. Analysis of data on the identification of PGC from the moment of initial detection in epiblast up to completion of migration to gonadal anlages was performed. Information on the PGC markers of the different stages of development, the mechanisms of PGC migration towards genital ridges and the chemokines that direct migration is discussed.

[The effect of retinoic acid on the meiosis in the chick embryo (Gallus gallus domesticus)]

In this study it was shown that the injection of retinoic acid (RA) into incubated eggs on day 9 or 14 induced entry the males germ cells into preleptotene stage of prophase I on day 17, which are absent in the control embryos. At the same time the meiosis marker SCP3 was detected in the germ cells. Which was also absent at control embryos. On day 19 in male embryos the number of male germ cells at the stage preleptoteny increased, but there were no germ cells in the following stages of the prophase of meiosis. In 20-day-old chicks meiotic germ cells were absent. Thus, white it is shown that the influence of RA on the developing chicken embryos induces the entry of germ cells into preleptotene stage of prophase I meiosis. However, further meiotic transformations don't occur. Thus RA is only one of many factors providing meiotic cell division.

The role of receptor tyrosine kinases in primordial germ cell migration

During embryonic development in Drosophila, rodents, and other organisms, primordial germ cells (PGCs) migrate from their points of origin to the nascent gonads, where they give rise to germ line stem cells. Receptor tyrosine kinase (RTK) activity is required for normal migration of primordial germ cells in both Drosophila and rodents. In this chapter, we discuss in vivo as well as in vitro methods which have been used to elucidate the role of the RTK Torso in Drosophila germ cell migration. Included are protocols for embryo collection, fixation, and immunostaining; the dominant female sterile technique; in vitro culture and observation of PGCs; pole cell transplantation; and labeling of pole cells for in vivo observation.

Abnormal epithelial cell polarity and ectopic epidermal growth factor receptor (EGFR) expression induced in Emx2 KO embryonic gonads

The gonadal primordium first emerges as a thickening of the embryonic coelomic epithelium, which has been thought to migrate mediodorsally to form the primitive gonad. However, the early gonadal development remains poorly understood. Mice lacking the paired-like homeobox gene Emx2 display gonadal dysgenesis. Interestingly, the knockout (KO) embryonic gonads develop an unusual surface accompanied by aberrant tight junction assembly. Morphological and in vitro cell fate mapping studies showed an apparent decrease in the number of the gonadal epithelial cells migrated to mesenchymal compartment in the KO, suggesting that polarized cell division and subsequent cell migration are affected. Microarray analyses of the epithelial cells revealed significant up-regulation of Egfr in the KO, indicating that Emx2 suppresses Egfr gene expression. This genetic correlation between the two genes was reproduced with cultured M15 cells derived from mesonephric epithelial cells. Epidermal growth factor receptor signaling was recently shown to regulate tight junction assembly through sarcoma viral oncogene homolog tyrosine phosphorylation. We show through Emx2 KO analyses that sarcoma viral oncogene homolog tyrosine phosphorylation, epidermal growth factor receptor tyrosine phosphorylation, and Egfr expression are up-regulated in the embryonic gonad. Our results strongly suggest that Emx2 is required for regulation of tight junction assembly and allowing migration of the gonadal epithelia to the mesenchyme, which are possibly mediated by suppression of Egfr expression.

Notch and Egfr signaling act antagonistically to regulate germ-line stem cell niche formation in Drosophila male embryonic gonads

Germ-line stem cells (GSCs) are maintained by the somatic microenvironment, or GSC niche, which ensures that GSCs can both self-renew and produce functional gametes. However, it remains unclear how the proper niche size and location are regulated within the developing gonads. In the Drosophila testis, the hub cells that form the GSC niche are derived from a subset of somatic gonadal precursors (SGPs) in the anterior portion of the embryonic gonad. Here we show that Notch signaling induces hub differentiation. Notch is activated in almost all SGPs in the male embryonic gonad, but Epidermal growth factor receptor (Egfr) is activated in posterior SGPs to repress hub differentiation, thereby restricting the expansion of hub differentiation in the embryonic gonad. We further show that Egfr is activated in posterior SGPs by Spitz ligand secreted from primordial germ cells (PGCs), whereas the Notch ligand Serrate is expressed in SGPs. This suggests that varying the number of PGCs alters niche size. Indeed, a decrease in the number of PGCs causes ectopic hub differentiation, which consequently increases their opportunity to recruit PGCs as GSCs. When ectopic hub differentiation is repressed, the decreased number of PGCs fails to become GSCs. Thus, we propose that SGPs sense PGC number via signals from PGCs to SGPs that modulate niche size, and that this serves as a mechanism for securing GSCs.

Cloning, identification, and expression analysis at the stage of gonadal sex differentiation of chicken miR-363 and 363*

miRNAs (microRNAs) are small, functional, non-coding RNAs and have been proved to implicate in regulation of diverse biological processes ranging from cell differentiation to organism development. With the purpose of exploring the roles of miRNAs on chicken embryo sexual determination and gonadal differentiation, we cloned and identified the stem-loop precursor structure (GenBank accession no. GU597370) of chicken miR-363 and 363* followed by studying their temporal and spatial expression patterns in chicken embryo at the stage of E3.5-6.5 d (embryonic days 3.5-6.5) by semi-quantitative RT-PCR and WISH (whole-mount in situ hybridization) in this study. The results showed that miR-363* located in cloned sequence of unknown segment in chicken genome, and flanking sequence of miR-363 and 363* according to the structural features of miRNAs precursor. Significantly differential expression (P < 0.05) of gga-miR-363 between female and male chicken embryonic gonads was found at E4.5 and 6.5 d, but the differential expression of gga-miR-363* from E3.5 to 6.5 d between both sexes fell short of significant level. The results of WISH indicated that expression signals of gga-miR-363 mainly appeared at limb bud, notochord, ectoderm, brain in E4.5 d chicken embryo, and urogenital systems (UGSs) at E6.5 d, and the expression level of E6.5 d was higher in the female than that in the male. It can be speculated that gga-miR-363 would involve in the gonadal development and gga-miR-363* might have transient regulatory functions during the early stages of chicken embryo development.

Mouse germ cell development: from specification to sex determination

Primordial germ cells (PGCs) are embryonic progenitors for the gametes. In the gastrulating mouse embryo, a small group of cells begin expressing a unique set of genes and so commit to the germline. Over the next 3-5 days, these PGCs migrate anteriorly and increase rapidly in number via mitotic division before colonizing the newly formed gonads. PGCs then express a different set of unique genes, their inherited epigenetic imprint is erased and an individual methylation imprint is established, and for female PGCs, the silent X chromosome is reactivated. At this point, germ cells (GCs) commit to either a female or male sexual lineage, denoted by meiosis entry and mitotic arrest, respectively. This developmental program is determined by cues emanating from the somatic environment.

Control of sex development

The process of sexual differentiation is central for reproduction of almost all metazoan, and therefore, for maintenance of practically all multicellular organisms. In sex development, we can distinguish two different processes, sex determination, that is the developmental decision that directs the undifferentiated embryo into a sexually dimorphic individual. In mammals, sex determination equals gonadal development. The second process known as sex differentiation takes place once the sex determination decision has been made through factors produced by the gonads that determine the development of the phenotypic sex. Most of the knowledge on the factors involved in sexual development came from animal models and from studies of cases in whom the genetic or the gonadal sex does not match the phenotypical sex, that is, patients affected by disorders of sex development (DSDs). Generally speaking, factors influencing sex determination are transcriptional regulators, whereas factors important for sex differentiation are secreted hormones and their receptors. This review focuses on these factors and whenever possible, references regarding the 'prismatic' clinical cases are given.

Gonadal tumours and DSD

Disorders of sex development (DSD), previously referred to as intersex, has been recognised as one of the main risk factors for development of type II germ cell tumours (GCTs), that is, seminomas/dysgerminomas and non-seminomas (e.g., embryonal carcinoma, yolk sac tumour, choriocarcinoma and teratoma). Within the testis, this type of cancer is the most frequent malignancy in adolescent and young adult Caucasian males. Although these males are not known to have dysgenetic gonads, the similarities in the resulting tumours suggest a common aetiological mechanism(s),--genetically, environmentally or a combination of both. Within the group of DSD patients, being in fact congenital conditions, the risk of malignant transformation of germ cells is highly heterogeneous, depending on a number of parameters, some of which have only recently been identified. Understanding of these recent insights will stimulate further research, with the final aim to develop an informative clinical decision tree for DSD patients, which includes optimal (early) diagnosis without overtreatment, such as prophylactic gonadectomy in the case of a low tumour risk.

Cadmium increases human fetal germ cell apoptosis

BACKGROUND

Cadmium (Cd) is a common environmental pollutant and a major constituent of tobacco smoke. Adverse effects of this heavy metal on reproductive function have been identified in adults; however, no studies have examined its effects on human reproductive organs during development.

OBJECTIVES

Using our previously developed organ culture system, we investigated the effects of cadmium chloride on human gonads at the beginning of fetal life, a critical stage in the development of reproductive function.

METHODS

Human fetal gonads were recovered during the first trimester (711 weeks postconception) and cultured with or without Cd. We used different concentrations of Cd and compared results with those obtained with mouse fetal gonads at similar stages.

RESULTS

Cd, at concentrations as low as 1 microM, significantly decreased the germ cell density in human fetal ovaries. This correlated with an increase in germ cell apoptosis, but there was no effect on proliferation. Similarly, in the human fetal testis, Cd (1 microM) reduced germ cell number without affecting testosterone secretion. In mouse fetal gonads, Cd increased only female germ cell apoptosis.

CONCLUSIONS

This is the first experimental demonstration that Cd, at low concentrations, alters the survival of male and female germ cells in humans. Considering data demonstrating extensive human exposure, we believe that current environmental levels of Cd could be deleterious to early gametogenesis.

Use of multiplanar 3-dimensional ultrasonography for prenatal sex identification

OBJECTIVE

Determination of fetal sex is an important part of detailed second-trimester ultrasonography. This task can be hindered by the fetal position, a low amniotic fluid volume, and advanced gestational age. Identification of fetal sex is further important in multiple gestations and prior histories of indeterminate-sex pregnancies. The goal of the study was to compare the effectiveness of 2-dimensional ultrasonography (2DUS) versus 3-dimensional ultrasonography (3DUS) at sex identification and to determine how genitalia measurements taken with 3DUS technology compare with measurements taken with 2DUS.

METHODS

A total of 111 patients at or beyond 16 weeks' gestation were recruited. Assignments of fetal sex using 2DUS and 3DUS were compared by the test of proportions. The actual neonatal sex was obtained after delivery. Given such small number of misdiagnoses by either 2DUS or 3DUS, the accuracies of the two modalities were not found to be statistically distinguishable from one another (P = .5585). The penile length, scrotal width, and bilabial diameter according to gestational age were measured and compared with previously published 2DUS data by t tests.

RESULTS

Sexes were assigned and interpreted in 65 cases. Ranges of genitalia measurements were plotted against gestational age and were found to be comparable with published data. There was a dramatic difference between the bilabial diameter and scrotal width with advancing gestational age that made sex determination much easier in the third trimester.

CONCLUSIONS

Although 3DUS did not have better prediction of fetal sex when compared with 2DUS, it may be a useful tool in conjunction with traditional imaging techniques in assigning fetal sex.

Congenital anomalies of the spleen from an embryological point of view

The spleen is the major accumulation of lymphoid tissue in the human body, an organ which prenatally produces and postnatally controls blood cells. Normally, a developed spleen lies in the upper left quadrant in parallel with the long axis of the 10th rib. It is a mesodermal derivate which first appears as a condensation of mesenchymal cells inside the dorsal mesogastrium at the end of the fourth embryonic week. Some congenital anomalies of the spleen are common, such as splenic lobulation and accessory spleen, while other conditions are rare, such as wandering spleen and polysplenia. Splenogonadal fusion is also a rare developmental anomaly, resulting from abnormal fusion of the splenic and gonadal primordia during prenatal development. The purpose of this article is to describe the normal development of the human spleen, supplemented with our own photomicrographs and a review of congenital anomalies of the spleen with their possible embryonic basis.

Long and winding roads: testis differentiation in zebrafish

Zebrafish sex determination, gonad differentiation and reproduction are far from being fully understood. Although the mode of sex determination is still being disputed, most experimental data point towards the lack of sex chromosomes and a multigenic sex determination system. Secondary effects from the environment and/or (xeno)hormones may influence the process, resulting in biased sex ratios. The exact time point of sex determination is unknown. Gonad differentiation involves a compulsory 'juvenile ovary' stage with subsequent transformation of the gonad into a testis in males. As the latter is a late event, there is a delay between sex determination and testis differentiation in zebrafish, in contrast to mammals. Information on the expression of several candidate genes thought to be involved in these processes has been supplemented with data from large-scale gonadal transcriptomic studies. New approaches and methodologies provide hope that answers to a number of important questions will be deciphered in the future.

[Biological characteristics of hematopoietic progenitor cells at different stages of hematopoietic development]

The aim of the present paper is to better understand the mechanism of hematopoietic development through studying the biological characteristics of hematopoietic progenitor cells at different stages of development. Firstly, the c-kit expression levels of the mononuclear cells from murine embryonic aorta-gonad-mesonephros (AGM) region at embryonic day (E)10.5 and E11.5, fetal liver (FL) at E12.5, E14.5, E16.5, E18 and bone marrow (BM) were assayed with fluorescence activated cell sorting (FACS). Secondly, hematopoietic progenitor cells derived from AGM at E10.5, FL at E14.5 and BM were isolated by using c-kit microbeads. Isolated c-kit(+) population cells from AGM, FL and BM were then co-cultured with E14.5 FL-derived stromal cells in transwell co-culture system in vitro. After 3, 7, 10 days of co-culture, numerous floating cells were generated. The floating cells generated in transwell inserts were collected for FACS cell count, migration activity detection and colony forming unit (CFU) formation assay. The results showed that the c-kit was highly expressed in E10.5 AGM, with the percentage of c-kit(+) cells declining during AGM development. c-kit expression was highly expressed again in E12.5 FL, declining along with the progressive development of the FL region. Co-cultured with FL-derived stromal cells, E10.5 AGM-derived c-kit(+) cells produced the highest number of hematopoietic cells, while BM-derived c-kit(+) cells produced the lowest number of hematopoietic cells. Compared with E10.5 AGM-derived c-kit(+) cells, E14.5 FL- and BM- derived c-kit(+) cells inclined to differentiate after 7 to 10 days of culture in vitro. E10.5 AGM and E14.5 FL-derived c-kit(+) cells exhibited a higher migration activity than BM-derived c-kit(+) cells. Moreover, E10.5 AGM-derived c-kit(+) cells showed a higher ability to form mixed colony-forming unit (CFU-Mix) colony. In conclusion, compared with FL- and BM-derived c-kit(+) cells, E10.5 AGM-derived c-kit(+) hematopoietic progenitor cells exhibit better proliferation, migration potential, and have a higher ability to maintain the undifferentiation state in vitro, providing an insight into their clinical manipulation.

An in-situ study of the impacts of urban wastewater on the immune and reproductive systems of the freshwater mussel Elliptio complanata

The goal of this study was to examine the disruptive effects of municipal effluents on the immune and reproductive systems of freshwater mussels. For 30 days, caged mussels were immersed in the Rivière des Mille Iles (Quebec, Canada), 150 m both upstream and downstream from two urban wastewater treatment plants: station F (Fabreville) and station A (Auteuil), which serve the city of Laval. Station F is 12 km upstream from station A. The immune and reproductive statuses of the mussels were thereafter determined. Though the weight/shell length ratio was not affected, the effluent induced mortality up to 60% at downstream sites. Total hemocyte counts increased, and phagocytosis and lysozyme activities were induced at station F, whereas these responses were suppressed at station A. Heterotrophic bacteria levels in mussels were negatively correlated with phagocytosis, showing the importance of this process in defending against infection. Inflammation biomarkers such as nitric oxide and cyclooxygenase activity were the same for all sites but were positively correlated with phagocytosis activity. The production of vitellogenin (Vtg)-like proteins was significantly induced at the site downstream from station A and was strongly associated with phagocytosis. This was further supported through analysis of covariance, of Vtg responses against phagocytosis, revealing that Vtg was no longer induced at the sites upstream and downstream from station A. The data support the contention that Vtg was involved, in part at least, in the immune system in mussels. Both Vtg and immune status are impacted by urban effluents and should be considered when using the Vtg biomarker to search for the presence of (xeno)estrogens in contaminated environments.