Apoptosis and cell proliferation are two important cellular processes known to be involved in the normal functioning of the testis in nonseasonally breeding mammals, but there is some controversy concerning their roles in the gonads of males from seasonally breeding species. We have studied the processes of apoptosis and cell proliferation in the testes of males of the Iberian mole (Talpa occidentalis), a species showing a strict seasonal reproduction pattern. Both males and females are sexually active during the winter and completely inactive in the summer, with two transitional periods, in the autumn and the spring. Adult males from these four reproductive stages were captured, and their testes were immunohistochemically studied for the presence of apoptotic and proliferation molecular markers as well for other testicular and meiotic cell-specific markers. We found that apoptosis varies in a season-dependent manner in the testes of male moles, affecting mainly late zygotene and pachytene cells during the period of sexual inactivity, but it does not differentially affect the number of Sertoli cells. More interestingly, apoptosis is not responsible for the massive germ-cell depletion occurring during mole testis regression. In addition, a wave of spermatogonial cell proliferation appears to restore the number of spermatogonia lost during the period of testis inactivity. According to current knowledge, data from moles indicate that mammals do not form a homogeneous group regarding the mechanisms by which the cell-content dynamics are regulated in the testes of males from seasonally breeding species.
Moles are unique among mammals because all females of several species of genus Talpa have bilateral ovotestes (gonads with both ovarian and testicular tissue). Based on the analysis of a large sample of embryos, foetuses and infants over a 13-year period, we have studied the development of the gonads in male and female moles of the species Talpa occidentalis. Several new field and laboratory procedures were developed specifically to obtain and manage this singular material. Our results reveal that gonads of female moles develop according to a testis-like pattern, which includes cord formation and mesonephric cell migration, and begins at the same time as testis differentiation in males. The first signs of sex differentiation do not appear in males but in females. Female (but not male) gonads are regionalised with a cortex (precursor of the ovarian tissue) and a medulla (precursor of the testicular tissue). Germ cells concentrate only in the cortex, so that the medulla soon becomes sterile. Testicular tissue development is transiently retarded in females for about a week before birth, and resumes afterwards. Development of the ovarian tissue in females is considerably delayed with respect to that of testicular tissue in both males and females. The molecular characterisation of peritubular myoid cells, which are exclusive of testes, evidences the presence of testicular tissue in the gonads of female moles, which also contain Leydig cells. However, the absence of fully differentiated Sertoli cells indicates that these cells are not responsible for triggering the differentiation of such a testicular tissue. Our results are also discussed regarding the definition of Sertoli cell morphology and function, and the possible role of germ cells in the sex-reversal process. Differences observed between XX and XY gonad development in moles suggest that the mammalian testis-determining gene, SRY, has an "anti-regionalisation" role during gonadal development, at least in those mammalian species in which regionalisation of the female gonad occurs.
SummaryBasement membranes (BMs) are specialized extracellular matrices required for tissue organization and organ formation. We study the role of laminin and its integrin receptor in the regulation of tissue migration during Drosophila oogenesis. Egg production in Drosophila involves the collective migration of follicle cells (FCs) over the BM to shape the mature egg. We show that laminin content in the BM increases with time, whereas integrin amounts in FCs do not vary significantly. Manipulation of integrin and laminin levels reveals that a dynamic balance of integrin-laminin amounts determines the onset and speed of FC migration. Thus, the interplay of ligand-receptor levels regulates tissue migration in vivo. Laminin depletion also affects the ultrastructure and biophysical properties of the BM and results in anterior-posterior misorientation of developing follicles. Laminin emerges as a key player in the regulation of collective cell migration, tissue stiffness, and the organization of anterior-posterior polarity in Drosophila.
Some cellular events are crucial in testis organogenesis, including Sertoli and Leydig cell differentiation, mesonephric cell migration and testis cord formation. These processes are controlled by transcription factors, paracrine signalling and hormones. Using the mole species Talpa occidentalis as an alternative animal model, we report the expression patterns of nine genes during testis differentiation and analyse their implications in the above-mentioned cellular processes. We show that: 1) Sertoli cell differentiation occurs very early and precedes mesonephric cell migration, indicating that the latter is not needed for the endocrine cytodifferentiation of Sertoli cells; 2) the time of Leydig cell differentiation is consistent with the participation of PDGFR-α in promoting the migration and/or proliferation of Leydig cell precursors, and with that of WNT4 signalling in inhibiting Leydig cell differentiation and 3) the formation of the tunica albuginea involves intragonadal cell migration/movement. These results demonstrate that testicular organogenesis in the mole differs from that in the mouse in some particular aspects, thus providing evidence that the spatio-temporal pattern of testis development is not highly conserved during mammalian evolution.
Hedgehogs belong to one of the several mammalian taxa in which karyotype differences are based on variations in heterochromatin content. Furthermore, the number and location of nucleolar organizer regions (NORs) can also vary widely. In the present study these cytogenetic features were investigated in the Algerian hedgehog, Erinaceus (Aethechinus) algirus. The heterochromatin and NOR distribution patterns in the karyotype of this species are new among hedgehogs, whereas the euchromatic regions, including their G-band pattern, are similar to those reported by others. In addition, silver staining revealed a cytogenetic feature exclusive to the heterochromatic blocks of E. algirus: their silver staining with standard cytogenetic procedures. Because no similar phenomenon has been described previously in a mammalian species, several hypotheses about the significance and specificity of silver staining to NOR sites are discussed. Finally, the existence of different types of heterochromatin in the species analysed here, lead us to propose that what hedgehogs have inherited from their common ancestor is a mechanism which permits the accumulation of heterochromatin on specific chromosomes, rather than the heterochromatin itself.
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