In male mammals, spermatogenesis proceeds for the reproductive lifetime of the animal. The continuation of this process depends upon a pool of spermatogenic stem cells within the testes that undergo asymmetric division to both maintain the stem cell population and give rise to progenitors that will proceed through spermatogenesis to generate mature spermatozoa. Thus, the development of functional spermatozoa may be divided into two distinct stages. The second, the process of spermatogenesis, is dependent upon the first, the successful formation of spermatogenic stem cells. Although spermatogenesis is characterized by marked cellular differentiation, the initial stages of germ line differentiation involve an avoidance of the differentiation signals acting during embryo development. The germ line is set aside early in embryo development and, while the primordial germ cells remain refractory to the differentiation signals affecting the soma, they undergo a number of phenotypic shifts before and after colonizing the genital ridge. Upon colonization of the genital ridge, the somatic tissue of the male genital ridge directs the final differentiation events that result in the formation of spermatogenic stem cells. It is this cell population that provides the basis for the maintenance of spermatogenesis in the adult.
C. Duffy and M. T. Kane
The aims of this study were to investigate in mouse embryonic stem cells (1) the requirement for myo-inositol for cell proliferation, (2) the incorporation of inositol into the phosphoinositides and inositol phosphates of the phosphatidylinositol (PtdIns) signal transduction system and (3) the effect of serum growth factors on PtdIns turnover. Exogenous myo-inositol was not essential for embryonic stem cell proliferation. Lithium, an inhibitor of endogenous inositol recycling, inhibited embryonic stem cell proliferation but this effect was not reversible by the addition of high concentrations of exogenous inositol. [3H]inositol was incorporated into the phosphoinositides, PtdIns, PtdIns4P and PtdIns(4,5)P2 in similar proportions as reported for other cells. [3H]inositol was also incorporated into a fourth lipid, tentatively identified as an inositolglycan. [3H]inositol was also incorporated into a number of inositol phosphates, with the greatest amount of incorporation after 24 h into an inositol pentakisphosphate. After serum starvation for 24 h, the addition of 10% whole or dialysed serum for 2 or 20 min increased (P < 0.05) incorporation into inositol trisand tetrakisphosphates. These results demonstrate the presence of PtdIns system components in embryonic stem cells and increased PtdIns turnover in response to serum growth factors.
Jae Yeon Hwang, Jong-Nam Oh, Dong-Kyung Lee, Kwang-Hwan Choi, Chi-Hun Park and Chang-Kyu Lee
OCT4 encoded by POU5F1 has a crucial role of maintaining pluripotency in embryonic stem cells during early embryonic development and several OCT4 variants have been identified in mouse and human studies. The objective of this study was to identify different variants of OCT4 and analyze their expression patterns in preimplantation porcine embryos and various tissues. In this study, we showed that POU5F1 transcribes its three variants, namely OCT4A, OCT4B, and OCT4B1. The OCT4B transcript consists of exons identical to the major form of the OCT4 variant, OCT4A, with a differential N-terminal domain-coding exon. The structure of OCT4B1 mRNA was the same as that of OCT4B mRNA, but harbored a cryptic exon. Based on these findings, the transcription levels were investigated and found that OCT4B and OCT4B1 made up ∼20% among the variants in the embryonic stage and this indicates that OCT4A mRNA is dominantly expressed during preimplantation embryo development. In addition, OCT4B mRNA was detected in all tissues examined, while OCT4A and OCT4B1 were detected only in testis but not in other tissues examined. OCT4B1 showed inversely correlated expression with SOX2 and NANOG expression. OCT4A protein was specifically localized to the nuclei, whereas OCT4B was mainly localized to the cytoplasm of the porcine embryos at the blastocyst stage. The findings of this study reveal that the porcine OCT4 gene can potentially encode three variants (OCT4A, OCT4B, and OCT4B1), and they are differentially expressed and would have roles dissimilar between each other in preimplantation embryos and various adult tissues.
Meng-Ling Liu, Jing-Lei Wang, Jie Wei, Lin-Lin Xu, Mei Yu, Xiao-Mei Liu, Wen-Li Ruan and Jia-Xiang Chen
Tri-ortho-cresyl phosphate (TOCP) has been widely used as plasticizers, plastic softeners, and flame retardants in industry and reported to have a deleterious effect on the male reproductive system in animals besides delayed neurotoxicity. Our preliminary results found that TOCP could disrupt the seminiferous epithelium in the testis and inhibit spermatogenesis, but the precise mechanism is yet to be elucidated. This study shows that TOCP inhibited viability of rat spermatogonial stem cells in a dose-dependent manner. TOCP could not lead to cell cycle arrest in the cells; the mRNA levels of p21, p27, p53, and cyclin D1 in the cells were also not affected by TOCP. Meanwhile, TOCP did not induce apoptosis of rat spermatogonial stem cells. After treatment with TOCP, however, both LC3-II and the ratio of LC3-II/LC3-I were markedly increased; autophagy proteins ATG5 and beclin 1 were also increased after treatment with TOCP, indicating that TOCP could induce autophagy in the cells. Ultrastructural observation under the transmission electron microscopy indicated that autophagic vesicles in the cytoplasm containing extensively degraded organelles such as mitochondria and endoplasmic reticulum increased significantly after the cells were treated with TOCP. In summary, we have shown that TOCP can inhibit viability of rat spermatogonial stem cells and induce autophagy of the cells, without affecting cell cycle and apoptosis.
R R, R Speed, M Taggart and HJ Cooke
Dazl knockout male mice are infertile because their germ cells are unable to complete the first meiotic prophase in the first wave of spermatogenesis and thereafter decrease in number due to a block at the A-aligned to A1 transition. The ability of the surviving somatic components of the testes to retain their function in the absence of mature germ cells was tested by injecting marked wild-type germ cell suspensions containing spermatogonial stem cells. Comparison of the frequency and extent of colonization of Dazl knockout testes with that of testes chemically depleted of germ cells showed little if any difference. It was concluded that Dazlko testes seem unimpaired in their ability to support spermatogenesis. Therefore, Dazlko testes provide a useful and reliable recipient in which to evaluate spermatogonial stem cells. The results furthermore demonstrate that the somatic compartment of the testis of these animals retains functionality.
Hong Wang, Liping Wen, Qingqing Yuan, Min Sun, Minghui Niu and Zuping He
Within the seminiferous tubules there are two major cell types, namely male germ cells and Sertoli cells. Recent studies have demonstrated that male germ cells and Sertoli cells can have significant applications in treating male infertility and other diseases. However, primary male germ cells are hard to proliferate in vitro and the number of spermatogonial stem cells is scarce. Therefore, methods that promote the expansion of these cell populations are essential for their use from the bench to the bed side. Notably, a number of cell lines for rodent spermatogonia, spermatocytes and Sertoli cells have been developed, and significantly we have successfully established a human spermatogonial stem cell line with an unlimited proliferation potential and no tumor formation. This newly developed cell line could provide an abundant source of cells for uncovering molecular mechanisms underlying human spermatogenesis and for their utilization in the field of reproductive and regenerative medicine. In this review, we discuss the methods for establishing spermatogonial, spermatocyte and Sertoli cell lines using various kinds of approaches, including spontaneity, transgenic animals with oncogenes, simian virus 40 (SV40) large T antigen, the gene coding for a temperature-sensitive mutant of p53, telomerase reverse gene (Tert), and the specific promoter-based selection strategy. We further highlight the essential applications of these cell lines in basic research and translation medicine.
Tetsuo Maruyama, Hirotaka Masuda, Masanori Ono, Takashi Kajitani and Yasunori Yoshimura
The human uterus mainly consists of the endometrium and the outer smooth muscle layer termed the myometrium. The uterus harbours the exceptional and remarkable regenerative ability responsible for cyclical regeneration and remodelling throughout the reproductive life. The uterus must swiftly and cooperatively enlarge to hold the growing foetus during pregnancy. Furthermore, the endometrium, in particular the functionalis layer, must also regenerate, differentiate and regress with each menstrual cycle under hormonal control. Endometrial regeneration from the basal layer is thought to contribute to replacement of the functionalis layer followed by its slough off during menses and parturition. These morphological and functional features of human endometrium can be reproduced in murine models in which severely immunodeficient mice are xenotransplanted with dispersed human endometrial cells under the kidney capsule. The uterine myometrium possesses the similar plasticity of the endometrium. This is demonstrated by multiple cycles of pregnancy-induced enlargement and regression after parturition. It is likely that regeneration and remodelling in the female reproductive tract are achieved presumably through endometrial and myometrial stem cell systems. Recent evidence now supports the existence of these stem cell systems in humans. Here, we will review our current understanding of uterine stem/progenitor cells. We also propose a novel hypothetical model in which stem cell activities explain the physiological remodelling and regeneration of the human uterus and the pathogenesis of gynaecological diseases such as endometriosis.
N. B. Hecht
Department of Biology, Tufts University, Medford, MA 02155, USA
Keywords: spermatogenesis; haploid gene expression; gene regulation; testis
Spermatogenesis offers an experimental system whereby the gene expression of eukaryotic cells with tetraploid, diploid, and haploid chromosome complements can be compared. Starting from a population of stem cells, the diploid spermatogonia follow one of two lineages. One subpopulation of cells initiates a differentiation process ultimately leading to the spermatozoon while a second, presumably distinct, subpopulation of spermatogonia enters a pathway that maintains and repopulates the stem cells of the testis. The cells destined to become spermatozoa undergo several spermatogonial divisions. The last complete replication of DNA during spermatogenesis, in the preleptotene primary spermatocyte, heralds the start of meiosis. During the lengthy interval of meiotic prophase, homologous chromosomes synapse and genetic recombination occurs, producing the genetic diversity required for survival of a species. Following meiotic recombination, the 4N spermatocytes divide twice
R Dimitrov, T Timeva, D Kyurkchiev, M Stamenova, A Shterev, P Kostova, V Zlatkov, I Kehayov and S Kyurkchiev
Human endometrium is an object of extensive restructuring and remodeling during the female reproductive life and it is quite tempting to assume that these periodic changes happen with the participation of cells that should have the basic characteristics of multipotent cells. The aim of this study was to search for the presence of cells with plastic adherence, clonogenicity, and differentiation in human endometrium. To this end, human endometrial stromal cells were cultured in vitro for more than 15 passages. Flow cytometry analysis of the cultured cells showed that they were positive for CD29, CD73 and CD90, which are considered to be the markers of cells with mesenchymal origin. The cells were negative for the hematopoietic cell markers (CD45, CD34, CD14, CD3, CD19, CD16/56, and HLA-DR). Further, it was shown that the cultured cells had 15% clonogenic efficiency and could be induced to differentiate into adipogenic cells containing typical lipid-rich vacuoles. These results demonstrate that the human endometrium contains a low number of cells with the characteristics of endometrial stromal stem/progenitor cells, which seem to belong to the family of the mesenchymal stem cells. It can be speculated that these cells are engaged into the monthly restructuring and remodeling of human endometrium.
Parag A Parekh, Thomas X Garcia and Marie-Claude Hofmann
Sertoli cells regulate male germ cell proliferation and differentiation and are a critical component of the spermatogonial stem cell (SSC) niche, where homeostasis is maintained by the interplay of several signaling pathways and growth factors. These factors are secreted by Sertoli cells located within the seminiferous epithelium, and by interstitial cells residing between the seminiferous tubules. Sertoli cells and peritubular myoid cells produce glial cell line-derived neurotrophic factor (GDNF), which binds to the RET/GFRA1 receptor complex at the surface of undifferentiated spermatogonia. GDNF is known for its ability to drive SSC self-renewal and proliferation of their direct cell progeny. Even though the effects of GDNF are well studied, our understanding of the regulation its expression is still limited. The purpose of this review is to discuss how GDNF expression in Sertoli cells is modulated within the niche, and how these mechanisms impact germ cell homeostasis.