RESUMO
Formation and subsequent break down of ovarian germ cell (GC) cysts is a key and an evolutionary-conserved developmental event, described in phylogenetically diverse species of invertebrates and vertebrates. In mammals, cyst break down (CBD) ends at the time of, or soon after, birth with the formation of primordial follicles enclosing single oocytes, which constitute the sole reservoir of gametes available through the whole female's reproductive life. In this study, we challenge this paradigm demonstrating the constitutive presence of a large number of cysts, enclosing two-thirty GCs, in the ovary of the adult armadillo Chaetophractus villosus, belonging to the superorder Xenarthra, one of the earliest offshoots among placentals. We also describe that (a) GCs enclosed within cysts are connected by intercellular bridges-intercellular bridges-markers of their clonal origin; (b) CBD occurs through four main phases, ending with primordial follicles containing single oocytes; (c) GCs encompass meiotic prophase I stages, from leptotene to diplotene; (d) seasonal variations in the number of GCs enclosed within cysts, suggesting the presence of a GC multiplying activity. The armadillo C. villosus''s ovary emerges as an extraordinary resource to investigate folliculogenesis and to explore the evolutionary past of the mammalian ovary.
Assuntos
Tatus/crescimento & desenvolvimento , Prófase Meiótica I/fisiologia , Oócitos/citologia , Oogênese/fisiologia , Folículo Ovariano/crescimento & desenvolvimento , Animais , Feminino , Folículo Ovariano/citologia , Estações do AnoRESUMO
The armadillo Chaetophractus villosus is a seasonal breeder whose seminiferous epithelium undergoes rapid regression with massive germ cell loss, leaving the tubules with only Sertoli cells and spermatogonia. Here, we addressed the question of whether this regression entails 1) the disassembly of cell junctions (immunolocalization of nectin-3, Cadm1, N-cadherin, and beta-catenin, and transmission electron microscopy [TEM]); 2) apoptosis (immunolocalization of cytochrome c and caspase 3; TUNEL assay); and 3) the involvement of Sertoli cells in germ cell phagocytosis (TEM). We showed a dramatic reduction in the extension of vimentin filaments associated with desmosomelike junctions at the interface between Sertoli and germ cells, and an increased diffusion of the immunosignals of nectin-3, Cadm1, N-cadherin, and beta-catenin. Together, these results suggest loss of Sertoli-germ cell adhesion, which in turn might determine postmeiotic cell sloughing at the beginning of epithelium regression. Then, loss of Sertoli-germ cell adhesion triggers cell death. Cytochrome c is released from mitochondria, but although postmeiotic cells were negative for late apoptotic markers, at advanced regression spermatocytes were positive for all apoptotic markers. Transmission electron microscopy analysis showed cytoplasmic engulfment of cell debris and lipid droplets within Sertoli cells, a sign of their phagocytic activity, which contributes to the elimination of the residual meiocytes still present in the latest regression phases. These findings are novel and add new players to the mechanisms of seminiferous epithelium regression occurring in seasonal breeders, and they introduce the armadillo as an interesting model for studying seasonal spermatogenesis.
Assuntos
Tatus/fisiologia , Adesão Celular/fisiologia , Células Germinativas/fisiologia , Epitélio Seminífero/fisiologia , Células de Sertoli/fisiologia , Animais , Apoptose/fisiologia , Caderinas/metabolismo , Caspase 3/metabolismo , Moléculas de Adesão Celular/metabolismo , Citocromos c/metabolismo , Imuno-Histoquímica , Marcação In Situ das Extremidades Cortadas , Junções Intercelulares/fisiologia , Masculino , Meiose/fisiologia , Microscopia Eletrônica de Transmissão , Nectinas , Fagocitose/fisiologia , Estações do Ano , beta Catenina/metabolismoRESUMO
Very little is known about the distinct reproductive biology of armadillos. Very few studies have investigated armadillo spermatogenesis, with data available only for Euphractus sexcinctus and Dasypus novemcinctus. In the present study, we analysed male germ cell differentiation in the large hairy armadillo Chaetophractus villosus throughout the year, describing a cycle of the seminiferous epithelium made of eight different stages. Evaluation of the testis/body mass ratio, analysis of the architecture of the seminiferous epithelium and the frequency of defective seminiferous tubules allowed identification of a temporal interruption of spermatogenesis during the period between mid-May to July (mid-end autumn) in correlation with very low testosterone levels. Overall, these results suggest that spermatogenesis is seasonal in C. villosus.
Assuntos
Tatus/fisiologia , Epitélio Seminífero/citologia , Espermatogênese , Animais , Argentina , Forma do Núcleo Celular , Montagem e Desmontagem da Cromatina , Masculino , Microscopia Eletrônica de Transmissão , Microtúbulos/metabolismo , Tamanho do Órgão , Estações do Ano , Epitélio Seminífero/crescimento & desenvolvimento , Epitélio Seminífero/metabolismo , Epitélio Seminífero/ultraestrutura , Células de Sertoli/citologia , Células de Sertoli/metabolismo , Células de Sertoli/ultraestrutura , Espermátides/citologia , Espermátides/crescimento & desenvolvimento , Espermátides/metabolismo , Espermátides/ultraestrutura , Espermatócitos/citologia , Espermatócitos/crescimento & desenvolvimento , Espermatócitos/metabolismo , Espermatócitos/ultraestrutura , Espermatogônias/citologia , Espermatogônias/crescimento & desenvolvimento , Espermatogônias/metabolismo , Espermatogônias/ultraestrutura , Testículo/citologia , Testículo/crescimento & desenvolvimento , Testículo/metabolismo , Testículo/ultraestrutura , Testosterona/sangue , Testosterona/metabolismoRESUMO
Meiosis is a complex type of cell division that involves homologous chromosome pairing, synapsis, recombination, and segregation. When any of these processes is altered, cellular checkpoints arrest meiosis progression and induce cell elimination. Meiotic impairment is particularly frequent in organisms bearing chromosomal translocations. When chromosomal translocations appear in heterozygosis, the chromosomes involved may not correctly complete synapsis, recombination, and/or segregation, thus promoting the activation of checkpoints that lead to the death of the meiocytes. In mammals and other organisms, the unsynapsed chromosomal regions are subject to a process called meiotic silencing of unsynapsed chromatin (MSUC). Different degrees of asynapsis could contribute to disturb the normal loading of MSUC proteins, interfering with autosome and sex chromosome gene expression and triggering a massive pachytene cell death. We report that in mice that are heterozygous for eight multiple simple Robertsonian translocations, most pachytene spermatocytes bear trivalents with unsynapsed regions that incorporate, in a stage-dependent manner, proteins involved in MSUC (e.g., gammaH2AX, ATR, ubiquitinated-H2A, SUMO-1, and XMR). These spermatocytes have a correct MSUC response and are not eliminated during pachytene and most of them proceed into diplotene. However, we found a high incidence of apoptotic spermatocytes at the metaphase stage. These results suggest that in Robertsonian heterozygous mice synapsis defects on most pachytene cells do not trigger a prophase-I checkpoint. Instead, meiotic impairment seems to mainly rely on the action of a checkpoint acting at the metaphase stage. We propose that a low stringency of the pachytene checkpoint could help to increase the chances that spermatocytes with synaptic defects will complete meiotic divisions and differentiate into viable gametes. This scenario, despite a reduction of fertility, allows the spreading of Robertsonian translocations, explaining the multitude of natural Robertsonian populations described in the mouse.