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PubMed2003

Chemotactic role of neurotropin 3 in the embryonic testis that facilitates male sex determination.

The first morphological event after initiation of male sex determination is seminiferous cord formation in the embryonic testis. Cord formation requires migration of pre-peritubular myoid cells from the adjacent mesonephros. The embryonic Sertoli cells are the first testicular cells to differentiate and have been shown to express neurotropin-3 (NT3), which can act on high-affinity trkC receptors expressed on migrating mesonephros cells. NT3 expression is elevated in the embryonic testis during the time of seminiferous cord formation. A trkC receptor tyrophostin inhibitor, AG879, was found to inhibit seminiferous cord formation and mesonephros cell migration. Beads containing NT3 were found to directly promote mesonephros cell migration into the gonad. Beads containing other growth factors such as epidermal growth factor (EGF) did not influence cell migration. At male sex determination the SRY gene promotes testis development and the expression of downstream sex differentiation genes such as SOX-9. Inhibition of NT3 actions caused a reduction in the expression of SOX-9. Combined observations suggest that when male sex determination is initiated, the developing Sertoli cells express NT3 as a chemotactic agent for migrating mesonephros cells, which are essential to promote embryonic testis cord formation and influence downstream male sex differentiation.

Animals↗
PubMed1988

Allometry of the kidney: implications for the ontogeny of osmoregulation.

In reptiles, there are two pairs of kidneys at birth: the mesonephros and the metanephros. The metanephric kidney in reptiles, as in all amniote vertebrates, is retained as the functional kidney in adults. However, the reptilian mesonephros does not degenerate until after birth, and its function during this time is unknown. In neonates of the iguanid lizard Sceloporus jarrovi, the metanephric kidney is only 63% as large as predicted from the allometric relationship between kidney mass and body mass in adults. However, the kidney mass of neonatal lizards conforms to this prediction if the mesonephric and metanephric masses are combined. Some other amniote vertebrates appear to follow this pattern as well: in marsupials, which retain the mesonephros for a short period after birth, the sum of mesonephric and metanephric mass in neonates conforms to the allometry of kidney mass on body mass for adults. In contrast, the mesonephros of eutherian mammals is degenerate at birth and the metanephric kidney alone is of the predicted size. That the scaling of kidney mass in neonatal lizards and marsupials is the same as that of adults only if the mass of both the mesonephros and metanephros are combined suggests that the mesonephric kidney in these vertebrates plays a significant role in the regulation of water and ion balance during development and for at least a short time after birth.

Animals↗
PubMed1999

Mesonephric kidney--a stem cell factory?

Mesonephros is a vestige, transient renal organ that functions only during embryonic development. The anatomy, position and even cellular fate of the mesonephric kidney varies drastically among mammalian species. The origin of mesonephros from intermediate mesoderm and the dependence of its differentiation on the nephric or Wolffian duct have been well established. Commonly accepted is also the mesonephric origin of epididymal ducts of the male reproductive tract. Recently, upon the more profound understanding of the molecular mechanisms involved in the development of the permanent mammalian kidney, some light has been shed over the molecular events taking place during the mesonephric development as well. Because of the functional and structural similarities between the mesonephric and metanephric kidneys, it is not surprising that many molecules regulating metanephric development are also activated during mesonephric development. However, the multifunctional nature of mesonephros has been unexpected. First, it serves as an embryonic secretory organ, in some mammalian species more so than in others. It is thereafter removed by programmed cell death. Second, it is a source of multiple stem cells including somatic cells in the male gonad, vascular endothelial cells, and hematopoietic stem cells. Thus, mesonephros is a challenging model for studies on epithelial differentiation and organogenesis, regulation of apoptosis, sex determination and stem cell differentiation. In this review, we focus in the molecular and stem cell aspects in the differentiation of the mammalian mesonephros.

Animals↗
PubMed1998

The Mayer-Rokitansky-Küster syndrome. An analysis of its morphology and embryology. Part II: Embryology.

The Müllerian duct (MD; ductus paramesonephricus) develops independent of the coelomic epithelium above the mesonephros. This part of the duct gives rise to the infundibulum with its fimbriated ostium abdominale. The part of the duct which lies along the mesonephros as far as its caudal pole makes a contribution to the ampulla and less often the isthmus. In the area of the mesonephros the MD fuses with the Wolffian duct (WD; ductus mesonephricus). The WD gives rise to the ampulla and the isthmus. Below the caudal pole of the mesonephros, as well as beyond the attachment point of the inguinal ligament of the mesonephros, the later round ligament of the uterus, the MD develops as an outgrowth of the WD and no longer as an independent structure. The MRK syndrome is, in its formal genesis, a non-fusion of the MD with the WD. This explains the fact that in a classic case of MRK syndrome, the Fallopian tube with a very small part of the cornu uteri extends only as far as the connection with the round ligament of the uterus. Different possibilities for the origin of MRK syndrome are discussed. It is suggested that the cause of the development of MRK syndrome could be a deficiency of gestagen and/or oestrogen receptors. This would also explain the various forms of the rudimentary vagina.

Female↗
PubMed2006

Role of mitotic, pro-apoptotic and anti-apoptotic factors in human kidney development.

The expression pattern of mitotic Ki-67 and anti-apoptotic bcl-2 proteins, as well as apoptotic caspase-3 and p53 proteins, were investigated in the human mesonephros and metanephros of 5-9 week-old human conceptuses. Apoptotic cells were additionally detected using the terminal deoxynucleotidyl transferase (TdT) nick-end labelling (TUNEL) method. Between the 5th and 7th developmental weeks Ki-67, caspase-3 and TUNEL-positive cells characterized all mesonephric structures, indicating importance of cell proliferation in the growth of the mesonephros and role of apoptosis in nephrogenesis. From the 7th week on, p53 and bcl-2 positive cells appeared in the mesonephros as well. Regressive changes in the mesonephros could be regulated by activation of p53, while bcl-2 could contribute to selective survival of some tubules giving rise to adult structures. In the early human metanephros (5-7 weeks), Ki-67 positive cells characterized all metanephric structures, indicating a role of cell proliferation in branching of the ureteric bud and in nephron formation. During the same period bcl-2, caspase-3 and TUNEL-positive cells were found only in the metanephric mesenchyme and nephrons. Bcl-2 protein probably protected nephrons from apoptosis, while caspase-3 protein controlled cell death in the mesenchyme. At later stages (7-9-weeks), appearance of p53-expressing cells could participate in further morphogenesis of the metanephric collecting system. The factors investigated had a spatially and temporally restricted pattern of appearance in developing kidneys. Changes in that pattern might lead to serious disturbances of kidney formation and function in early childhood.

Apoptosis↗
PubMed2005

Mesonephric FGF signaling is associated with the development of sexually indifferent gonadal primordium in chick embryos.

The gonad as well as the reproductive tracts, kidney, and adrenal cortex are derived from the intermediate mesoderm. In addition, the intermediate mesoderm forms the mesonephros. Although the mesonephros is the source of certain testicular cell types, its contribution to gonad formation through expression of growth factors is largely unknown. Here, we examined the expression profiles of FGF9 in the developing mesonephros of chick embryos at sexually indifferent stages, and found that the expression domain is adjacent to the gonadal primordium. Moreover, FGFR3 (FGF receptor 3) showed a strong expression in the gonadal primordium. Next, we examined the functions of FGF signal during gonadal development with misexpressed FGF9. Interestingly, misexpression of FGF9 led to gonadal expansion through stimulation of cell proliferation. In contrast, treatment with a chemical inhibitor for FGFR decreased cell proliferation and resulted in reduction of the gonadal size. Simultaneously, the treatment resulted in reduction of gonadal marker gene expression. Our study demonstrated that FGF expressed in the developing mesonephros is involved in the development of the gonad at the sexually indifferent stages through stimulation of gonadal cell proliferation and gonadal marker gene expression.

Animals↗
PubMed1992

Sites of estrogen uptake in embryonic Trachemys scripta, a turtle with temperature-dependent sex determination.

Female sex determination can be induced in embryonic red-eared slider turtles (Trachemys scripta) by exogenous estrogen, as well as by incubation at warm temperature. In the present study, estrogen target areas were identified in embryos before (stage 15), during (stage 18), and after (stage 22) the critical period for sex determination. Both hyperfilm and emulsion autoradiography were used to localize tritium accumulation after the injection of radiolabeled 17 beta-estradiol. Site-specific tritium-labelling was found at all stages, notably in the mesonephros at stage 15, in the mesonephros and oviduct at stage 18, and in the mesonephros, oviduct, and the interrenal gland at stage 22. Few if any cells in the gonad were tritium-labeled at any stage. The large number of estrogen-concentrating cells in the mesonephros and interrenal and the lack of binding to gonadal tissues indicates that estrogen action on gonadal differentiation during the period of sex determination may be indirect.

Animals↗
PubMed1988

The development of the sexually indifferent gonad in the prosimian, Galago crassicaudatus crassicaudatus.

The morphogenesis of the sexually indifferent gonad of the primate Galago crassicaudatus crassicaudatus was studied by high-resolution light microscopy and electron microscopy in 15 embryos aged 26 to 33 days. Onset of gonadal development follows the morphogenesis of the mesonephros by a conspicuous interval and is identified as the time when the first primordial germinal cells arrive in the region ventral to the central third of the mesonephros; this is followed by intense proliferation of the coelomic mesothelial cells lining the area. They become organized into short piles that deepen in the underlying mesenchyme, enclosing the germinal cells in the process. Rapidly, the piles become confluent forming a compact mass, the gonadal blastema, which is soon cleaved into gonadal cords by stroma and vascular lacunae. The mesonephros becomes involved in the morphogenesis of the gonad only in late stages of development when anatomic continuities become established between the capsules of its regressing glomeruli and the elongating gonadal rete cords. These observations show that in the Galago the somatic cells of the gonadal blastema, i.e., the precursors of the definitive testicular and ovarian sustentacular cells, derive from the coelomic mesothelium in contrast to other mammals, e.g., ruminants and rodents, where they are of mesonephric derivation. This important point is discussed in light of the differences that exist among species with regard to the structural complexity, functionality, and stages of differentiation/involution of their mesonephroi on the one hand, and the time of gonadal development on the other.

Animals↗
PubMed1975

Morphology of the epididymis of the cock (Gallus domesticus) and its effect upon the steroid sex hormone synthesis. I. Ontogenesis, morphology and distribution of the epididymis.

The epididymis of the cock is divided into a main part and an appendix epididymidis. The main part of the epididymis is firmly connected to the testis. The sperm transporting tubes open into the ductus epididymidis along its entire length. The rete testis, as the most proximal part of the epididymis, develops from mesenchym cells. The rete testis connects the tubuli seminiferi with the ductuli efferentes proximales which develop from the Bowman's capsules of the mesonephros. The ductuli efferentes distales develop from the proximal tubules, conducting segments (loops of Henle), and the distal tubules of the mesonephros. The short ductuli conjugentes which open into the ductus epididymidis, originate from the connecting segments of the mesonephros. In the sexually mature cock the rete testis, the ductuli efferentes proximales, and the ductus epididymidis all show an enlargement in the lumen. In the ductuli efferentes proximales and in the ductus epididymidis one can observe a formation of globuli and cell protrusion which lead to a loss of the surface structure of the epithelial cells. The appendix epididymidis and the capsula fibrosa of the adrenal gland are joined by connective tissue. The appendix epididymidis consists of the blindly ending ductus aberrans (the crainal continuation of the ductus epididymidis) and the ductuli aberrantes which open into the ductus aberrans. The blind ends of the ductuli aberrantes end in the capsula fibrosa of the adrenal gland.

Animals↗
PubMed1989

On cell contribution to gonadal soma formation in quail-chick chimeras during the indifferent stage of gonadal development.

A quail mesonephros was produced in a chicken embryo by orthotopic transplantation of quail left Wolffian duct and intermediate mesoderm between somites 18 and 21 in a 2 day chicken embryo. During the indifferent period of gonadal development in the chicken (day 4-6), no mesonephric (quail) cells take part in forming gonadal somatic cells. At this period all these cells are derived from the surface epithelium. The epithelial cells leave the surface where colonization of primordial germ cells occurs. The mesonephros begins its participation in gonadal soma formation between day 6 and 7, the time of sexual differentiation. These results are discussed in terms of sexual differentiation and the development stage of the mesonephros.

Animals↗
PubMed2001

Toxicity of PCB-126 in European flounder (Platichthys flesus) with emphasis on histopathology and cytochrome P4501A induction in several organ systems.

A series of experiments was set up to elucidate the effects of pollution on marine and estuarine fish health, since the European flounder (Platichthys flesus) has shown a relatively high prevalence of (pre)neoplastic liver lesions and lymphocystis virus disease in Dutch coastal and estuarine waters. The hypothesis of a causal relationship between pollution and the above-mentioned diseases was supported by results from semi-field experiments. Therefore several laboratory experiments were carried out to substantiate causality further and to identify the xenobiotics that may play a major role in the field. The present study focuses on polychlorinated biphenyls (PCBs). European flounders (Platichthys flesus) were orally exposed to a single dose of 0, 0.5, 5 or 50 mg PCB-126/kg body weight under controlled laboratory conditions. The effects on liver, gills, gastrointestinal tract, gonads, spleen and mesonephros were examined histologically after 16 days. Induction and localization of cytochrome P4501A (CYP1A) immunoreactivity, and effects on hepatocyte proliferation were visualized immunohistochemically. Effects on thymus size were examined by morphometric analysis of serial sections. Three out of five animals of the highest dose group showed haemorrhages in the fins and tail after 16 days. All animals showed reduced activity in the later stages of the experiment, and some animals of the highest dose group discontinued feeding 14 days after exposure. Strong and exposure-related induction of CYP1A immunoreactivity was noted in hepatocytes, endothelium in all organs examined, and epithelium of the digestive tract and mesonephros at PCB-126 levels of 0.5, 5 and 50 mg/kg. In addition, the strong induction of CYP1A immunoreactivity in a distinct population of haematopoietic cells in the mesonephros and in circulating blood is remarkable, and has not been described previously in other fish species. Furthermore, a morphometrically determined significant reduction in relative thymus size was noted in animals exposed to 50 mg PCB-126/kg. Although the functional implications for the immune system of this reduction need to be further investigated, an impact on the specific resistance against infectious diseases as observed in the field, e.g. viral lymphocystis disease, is not implausible. In addition, a significant increase in absolute liver weight, in hepatosomatic index, and in number of proliferating hepatocytes [measured as immunoreactivity against proliferating cell nuclear antigen (PCNA)] was noted in animals of the highest dose group. From these findings we suppose that PCB-126 (and related chemicals) may play a role in the promotion of tumour development in the liver of European flounders as observed in the field. The results of the present experiment show relatively stronger effects than effects previously reported from experiments with TCDD, suggesting that the TEF of 0.005 assigned to PCB-126 from early life stage mortality experiments in rainbow trout (Oncorhynchus mykiss), underestimates the toxic potential of PCB-126.

Animals↗
PubMed2006

Activin A is an endogenous inhibitor of ureteric bud outgrowth from the Wolffian duct.

Development of metanephric kidney begins with ureteric bud outgrowth from the Wolffian duct (WD). GDNF is believed to be a crucial positive signal in the budding process, but the negative regulation of this process remains unclear. Here, we examined the role of activin A, a member of TGF-beta family, in bud formation using an in vitro WD culture system. When cultured with the surrounding mesonephros, WDs formed many ectopic buds in response to GDNF. While the activin signaling pathway is normally active along the non-budding WD (as measured by expression of activin A and phospho-Smad2/3), activin A was absent and phospho-Smad2/3 was undetectable in the ectopic buds induced by GDNF. To examine the role of activin A in bud formation, we attempted to inactivate activin action. Interestingly, the addition of neutralizing anti-activin A antibody potentiated GDNF action. To further clarify the role of activin A, we also tested the effect of activin blockade on the WD cultured in the absence of mesonephros. WDs without mesonephros did not form ectopic buds even in the presence of GDNF. In contrast, blockade of activin action with a variety of agents acting through different mechanisms (natural antagonist, neutralizing antibodies, siRNA) enabled GDNF to induce ectopic buds. Inhibition of GDNF-induced bud formation by activin A was accompanied by inhibition of cell proliferation, reduced expression of Pax-2, and decreased phosphorylation of PI3-kinase and MAP kinase in the WD. Our data suggest that activin A is an endogenous inhibitor of bud formation and that cancellation of activin A autocrine action may be critical for the initiation of this process.

Activins↗
PubMed2006

Identification of a novel population of adrenal-like cells in the mammalian testis.

Steroidogenic cells of the adrenal and gonad are thought to be derived from a common primordium that divides into separate tissues during embryogenesis. In this paper, we show that cells with mixed adrenal and Leydig cell properties are found dispersed in the insterstitium of the embryonic and adult mouse testis. They express the adrenal markers Cyp11b1 and Cyp21 and respond to ACTH. Consistent with these properties, we show that the embryonic testis produces the adrenal steroid corticosterone. These cells also express Cyp17 and respond to hCG stimulation but do not express the Leydig specific marker Insl3 showing that they are a population of steroidogenic cells distinct from Leydig cells. Based on their properties, we refer to these cells as adrenal-like cells of the testis and propose that they are the mouse equivalent of the precursors of human adrenal rests, tumors found primarily in male patients with congenital adrenal hyperplasia. Organ culture studies show that ACTH-responsive cells are present at the gonad/mesonephros border and seem to migrate into the XY but not the XX gonad during development. Consistent with this, using transgenic Cyp11a1 reporter mice, we definitively show that steroidogenic cells can migrate from the mesonephros into the XY gonad. We also show that the region between the mesonephros and the gonad harbors steroidogenic cell precursors that are repressed by the presence of the mesonephros. We propose that this region is the source of the adrenal-like cells that migrate into the testis as it develops and are activated when Leydig cells differentiate. These studies reveal the complex nature of steroidogenic cell differentiation during urogenital development.

Adrenal Glands↗
PubMed1984

Cytoplasmic microtubules of normal and tumor cells of the leopard frog. Temperature effects.

The cytoplasmic microtubule complex (CMTC) was examined in monolayer cultures of normal tadpole mesonephros, primary renal adenocarcinoma, and an established cell line derived from a pronephric renal adenocarcinoma (PNKT-4B) of the leopard frog, Rana pipiens. Immunocytochemistry revealed typical arrays of microtubules extending from the cytocentrum to the cell periphery in all three cell types when cultured at 28 degrees C; similar results were obtained at 20 degrees C. However, the CMTC was disorganized in both tumor types, in contrast to the retention of a typical CMTC in normal tissue cultured at 7 degrees C. The response of PNKT-4B cells differed from that of normal tadpole mesonephros when treated with the microtubule inhibitor drug nocodazole. At 28 degrees C, PNKT-4B and tadpole mesonephros cells lost their CMTC with nocodazole treatment, and both were able to reconstitute CMTC when nocodazole was removed. Similarly, both lost CMTC organization with nocodazole and culture at 70 degrees C. However, while normal cells could effect a recovery at 7 degrees C after the removal of nocodazole, PONKT-4B cells were unable to restructure CMTC under the same conditions. Metastasis in the frog renal adenocarcinoma is temperature-dependent, with an elevated prevalence of metastasis in tumor-bearing frogs maintained at 28 degrees C. Few metastatic colonies are detected in tumor-bearing frogs maintained at a low temperature (7 degrees C). Other studies have indicated that microtubules, which are essential for cell motility, play an important role in the invasion by tumor cells of normal tissue fragments in vitro. The effects of temperature on metastasis of the Lucke renal adenocarcinoma are consistent with temperature-mediated changes in tumor-cell CMTC.

Adenocarcinoma↗
PubMed2006

Sprouty2 is involved in male sex organogenesis by controlling fibroblast growth factor 9-induced mesonephric cell migration to the developing testis.

Fibroblast growth factor 9 (FGF9) signal has a role in organogenesis of the mammalian testis by controlling migration of mesonephric cells to the XY gonad, but neither it nor the FGF receptors is expressed sex-specifically. Of the Sprouty genes encoding antagonists of receptor tyrosine kinases including FGFr, mSprouty2 expression was confined to the developing testis and mesonephros. Gain of SPROUTY2 function in the male genital ridge and mesonephros malformed the vas deferens and epididymis, and diminished the number of seminiferous tubules and interstitium associating with reduced mesonephric cell migration and Fgf9 expression in embryonic testis, whereas exogenous FGF9 signaling recovered mesonephric cell migration inhibited by SPROUTY2. These phenotypes associated also with the decreased expression of Sox9, Desert hedgehog, Hsd3beta, Platelet/endothelial cell adhesion molecule, and alpha-smooth muscle actin, which are markers of the Sertoli, Leydig, endothelial, and peritubular myoid cells of the developing testis. Based on these data, we propose that the Sprouty proteins are involved normally in mediating the sexually dimorphic signaling of FGF9 and controlling cell migration from the mesonephros during testis development.

3-Hydroxysteroid Dehydrogenases↗
PubMed2000

Peroxisomes in permanent and provisional kidneys. Phylogenic and ontogenic considerations.

Peroxisomes in three forms of vertebrate kidney (pronephros, mesonephros, and metanephros), as permanent or provisional kidney, are summarized concerning their ultrastructure and developmental changes. Because the peroxisome is known to be diverse in mammalian metanephros, and species difference is its distinctive feature among cell organelles, information should be obtained on each kidney of each species. The ultrastructural and biochemical features of peroxisomes have at least been partly delineated in the metanephros and mesonephros, but nothing is known about the pronephros. Ultrastructural studies of the metanephric peroxisomes are present in mammals, birds, and reptiles, but information on their development is restricted to mammals and birds. As for the mesonephric peroxisomes, both ultrastructural and developmental data have been accumulating on mammals and amphibians, and ultrastructural information is present on fishes, but not on birds and reptiles. At present, studies on peroxisomes of provisional kidney have been restricted to mammalian mesonephros. The common features of renal peroxisomes previously examined are that they are spherical cell organelles with a single limiting membrane in ultrastructure, and are positive for catalase. Information on the ultrastructure and enzymes is not sufficient at present for comparing the ontogenesis of renal peroxisomes with their phylogenesis.

Animals↗
PubMed1999

Stem cell factor and c-kit gene expression and protein localization in the sheep ovary during fetal development.

The aim of this study was to investigate stem cell factor and c-kit gene expression and protein localization in the mesonephros and ovary of sheep fetuses at different days of gestation, using RNA in situ hybridization and immunohistochemical procedures. At days 24 and 26 of gestation, stem cell factor mRNA and protein were present in cells throughout the developing gonad and mesonephros. From day 28 to day 40 of gestation, stem cell factor mRNA and protein became increasingly localized to the cortical region of the ovary, where most germ cells were present as actively proliferating oogonia. From day 40 to day 90 of gestation, stem cell factor mRNA and protein localization were confined mainly to the ovarian cortex. Moreover, within the cortical region, stem cell factor mRNA was low or absent where follicles were first forming and highest in the outer ovarian cortex, where germ cells were undergoing mitosis or the early stages of meiosis. In contrast, stem cell factor protein was present in newly forming follicles, as well as in mitotic and meiotic germ cells, which is consistent with the presence of both membrane-bound and soluble forms of this ligand. However, by day 90 of gestation, both stem cell factor mRNA and protein were observed in the granulosa cells of most (> 90%) primordial follicles. C-kit mRNA and protein were observed from day 24 of gestation in both germ cells and somatic cells but, with increasing gestational age, preferentially in germ cells (for example, pre-meiotic germ cells and both isolated oocytes and follicle-enclosed oocytes). C-kit protein, but not mRNA, was also observed in germ cells that were undergoing meiosis. The results indicate that the cells containing stem cell factor mRNA within the ovary up to day 90 of gestation originated from the gonadal blastema and from cells that migrated from the mesonephros before day 28 of gestation. Since stem cell factor mRNA was absent in both mesonephric cells migrating after day 28 of gestation and in regions where follicles were first forming, it is suggested that these later migrating mesonephric cells are the progenitors of the granulosa cells in the first forming follicles. In conclusion, during follicle formation, c-kit mRNA is localized to germ cells whereas c-kit, together with stem cell factor protein, is localized to both germ cells and somatic cells, consistent with the hypothesis that the presence of this receptor-ligand pair is essential to prevent apoptosis.

Animals↗
PubMed1983

Dual contribution of embryonic ventral blood island and dorsal lateral plate mesoderm during ontogeny of hemopoietic cells in Xenopus laevis.

The early embryonic development of hemopoietic cells in Xenopus laevis was examined. Either dorsal lateral plate (DLP) or ventral blood island (VBI) mesoderm was reciprocally transplanted between cytogenetically distinct (2N or 3N) stage 14 to 19 (neural fold) embryos. F-DNA content of circulating erythrocytes was assayed at stages 40, 41, 43, 45, and 49. The F-DNA content of cells in the thymus and mesonephros was assayed at stage 49. F-DNA values were used to distinguish between donor or host origin of hemopoietic cells in individual animals. The results demonstrated that DLP mesoderm gave rise to a population of stem cells that colonized the thymus and mesonephros, but not the blood. VBI mesoderm gave rise to a population of stem cells that colonized the blood and thymus, but not the mesonephros. These experiments show that there are two stem cell compartments in the amphibian embryo, separated in both space and time.

Animals↗