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Testicular germ cell apoptosis and spermatogenesis
Published in Rajender Singh, Molecular Signaling in Spermatogenesis and Male Infertility, 2019
Successful completion of spermatogenesis ensures the production of a highly differentiated cell, the spermatozoon, which functions as a delivery vehicle for the paternal DNA to the oocyte. Production of a single spermatozoon is a very complex but well-organized process, which takes place in the testis and can broadly be divided into three phases. The first phase is the proliferative phase, during which spermatogonial stem cells undergo mitotic divisions to maintain the stem cell population and to produce spermatogonia cells ready to proceed for spermatogenesis (1,2). Thus, the proliferative phase is strongly committed to a cyclic and continual expansion of spermatogonia (3,4). The first division of spermatogenesis is known as spermatocytogenesis, and its function is to maintain a pool of stem cells and to produce spermatogonia for further proliferation and differentiation (5,6). Three types of spermatogonia have been described, which are type-A spermatogonia, intermediate-type and type-B spermatogonia (7–9). Type-A spermatogonia are primitive spermatogonia due to the absence of heterochromatin, while the intermediate spermatogonia have a lower amount of heterochromatin. Type-B spermatogonia possess a higher amount of heterochromatin and are highly differentiated. Type-A spermatogonia can be subdivided into A-single, A-paired and A-aligned spermatogonia, which differ only in their topographical arrangement on the basement membrane of the seminiferous tubule. Type-B spermatogonia enter into the meiosis phase by giving rise to primary spermatocyte after the mitotic division (8–10).
Influence of Environmental Agents on Male Reproductive Failure
Published in Vilma R. Hunt, Kathleen Lucas-Wallace, Jeanne M. Manson, Work and the Health of Women, 2020
Sperm production is affected by many factors such as general health, age, frequency of ejaculation, season of the year, temperature, photoperiod, nutrition, stress, and toxic substances.81 The process of spermatogenesis can be divided into three principal phases: spermatocytogenesis, meiosis, and spermiogenesis. In spermatocytogenesis, spermatogonia proliferate by mitosis to give rise to new stem cells to replace those removed from the population by differentiation into spermatocytes (Figure 3). There are two types of spermatogonial stem cells: those which serve as an emergency source of new stem cells (reserve) and those which proceed to differentiate into spermatocytes (renewing). Reserve stem cells remain quiescent unless the supply of renewing stem cells is depleted through formation of B, spermatogonia which differentiate into primary spermatocytes. Type A spermatogonia may degenerate during mitotic divisions so that the total number of spermatozoa produced is less than the number of Type A spermatogonia present at the beginning of spermatogenesis.81 In Sprague-Dawley rats, there is a total cell loss of 22% between late spermatogonial and advanced spermatid stages. In man, a cell loss of 35% from early spermatocyte to the spermatid stage has been reported.89 The testis selects against many more potential gametes than the number allowed to complete spermatogenesis during these early stages. Evidence suggests that a considerable amount of selection in the testis is against spermatogonia with abnormal chromosomes. Studies have shown that the incidence of polyploid spermatogonia is very high in mice but that polyploid primary spermatocytes are seldomly observed.89 Degenerating spermatogonia are phagocytized by Sertoli cells.
The effects and molecular mechanism of heat stress on spermatogenesis and the mitigation measures
Published in Systems Biology in Reproductive Medicine, 2022
Yuanyuan Gao, Chen Wang, Kaixian Wang, Chaofan He, Ke Hu, Meng Liang
Spermatogenesis is a complex process involving mitosis and meiosis (Gunes et al. 2015). Spermatogenesis is the process of the reproduction and differentiation of germ cells in the seminiferous tubules of the testis, which is divided into three parts: spermatocytogenesis, meiosis, and spermiogenesis (Staub and Johnson 2018). Studies have shown that the process of spermatogonium differentiation into sperm is very complex and requires the participation of many factors, including hormones and growth factors, and especially the strict control of the temperature inside the testis (Rajender et al. 2011; Neto et al. 2016). Epigenetic modification is an important regulator of many biological processes, including spermatogenesis. Common types of epigenetic modifications are DNA methylation, histone modification, and chromatin remodeling (Güneş and Kulaç 2013). Epigenetic variation has been shown to have an important effect on spermatogenesis and may lead to male infertility. The hypermethylation of some testicular-specific genes has been reported to lead to altered semen parameters or infertility in men (Rajender et al. 2011). In addition, the normal occurrence of sperm cannot be separated from the regulation of endocrine and paracrine mechanisms. The endocrine system stimulates spermatogenesis through the secretion of follicle stimulating hormone (FSH) and luteinizing hormone (LH), which induces the production of normal sperm (de Kretser et al. 1998). At present, a growing body of research shows that, although the stimulation of hormone signaling is indispensable for spermatogenesis, some growth factors and cytokines are also essential for this process (Syriou et al. 2018; Zhou et al. 2019).
Verbascoside attenuates experimental varicocele-induced damage to testes and sperm levels through up-regulation of the hypothalamus-pituitary-gonadal (HPG) axis
Published in Pharmaceutical Biology, 2021
Letian Han, Shan Xiang, Baohai Rong, Yanchen Liang, Shengtian Zhao
VB doses administered to rats in this study were selected based on previous reports (Amin et al. 2016). The period of VCL damage induction was chosen according to previous studies (Soni et al. 2018; Karna et al. 2019). The full spermatogenic cycle, including spermatocytogenesis, meiosis, and spermiogenesis, requires 40–45 days in the rat model, and the epididymal transit of spermatozoa takes approximately 1 week in rats (Türk et al. 2016; Dehghani et al. 2019); thus, the treatment period was set at 58 days.