Archive | 2019
The Developmental Process of Spermatogenesis
Abstract
The multiplication and development of germ cells in the seminiferous tubules of the testiclesoccur through a complex series of cellular events that are controlled by multiple signals. It is composed of 6 stages in humans (Figure 1). Spermatogonial stem cells are self-renewed via mitosis, meiosis and contribute to the formation of haploid spermatids from diploid spermatocytes. Through the process of spermiogenesis, spermatids undergo maturation and are transformed into functional spermatozoa which are released at spermiation after the breakage of intercellular bridges attaching the spermatids to Sertoli cells. Spermatogenesis is a continuous process requiring the contribution of numerous cell and regulatory factors. Its understanding is essential in order to advance research for treatment of male infertility. The different stages of spermatogenesis along with the main roles of Sertoli cell and BTB will be reviewed. Some emerging fields in research regarding the new classification was briefly examined for a better understanding of the complexity of the process. Goetz Egloff1*, Isabella Bender2, and Jasmin Roemer3 Dalia K1, Ali K2 and Ghina G1* 1Department of Obstetrics and Gynecology, American University of Beirut Medical Center, Lebanon 2Division of Gynecologic Oncology, American University of Beirut Medical Center, Lebanon *Address for Correspondence Ghazeeri G, Division of Reproductive Endocrinology and Infertility, Department of Obstetrics & Gynecology, American University of Beirut Medical Center, Hamra, Beirut, PO BOX: 113-6044 Lebanon, Telephone: 01-350000, E-mail: [email protected] Submission: 25 September, 2019 Accepted: 9 October, 2019 Published: 18 October, 2019 Copyright: © 2019 Dalia K. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Review Article Open Access spermatogenesis [7]. The Blood-Testis Barrier (BTB) is situated within the basement membrane of the ST, providing the microenvironment for the emergence of spermatids [8]. This barrier is well established at puberty, concomitantly with the onset of meiosis [9]. The basal and the ad-luminal compartments are the compartments found in the Seminiferous Epithelium (SE) which are separated by the BTB. The basal compartment includes undifferentiated spermatogonia (A and B) and preleptotene spermatocytes. The ad-luminal compartment is inhabited by the primary, secondary spermatocytes, haploid spermatids and spermatozoa. During the 6 stages of spermatogenesis, the junctions between Sertoli cells and reproductive cells are in a constant remodeling process to allow transportation through the SE. It is in the ad-luminal compartment that meiosis I and II, the formation up to the spermatozoa stage and spermiation take place [10]. The different stages of the epithelial cycle In humans, spermatogonia enter spermatogenesis every 16 days, divide in a continuous way through mitosis to produce different variety of cells. This is entitled “cycle of the seminiferous epithelium” [11]. The detail inspection of cross sections of tubules over the years uncovered 6 main stages of spermatogenesis or cellular associations[12]. Cycle of the Seminiferous Epithelium The epithelial cycle is composed of 6 different stages along the SE of the testis [13]. A stage refers to a specific segment of the SE over time [14]. The duration of spermatogenesis is around 64 days in which a type A spermatogonia is transformed into multiple haploid spermatozoa [15]. In this context, an epithelial cycle takes 16 days to be completed, yet it takes four cycles for a spermatogonia to become a spermatid along the section of a tubule (74 days). Spermatogonial proliferation and spermatocytes formation Two types of spermatogonia (A and B) are present in the basal Introduction Spermatogenesis is a process occurring in the Seminiferous Tubules (ST) of the testicles. The multiplication and development of germ cells occur through a complex series of cellular events that are controlled by multiple signals. While fourteen stages are found in rats, the seminiferous epithelial cycle is composed of 6 stages in humans [1]. Spermatogonial stem cells are self-renewed via mitosis, meiosis (I and II) and contribute to the formation of haploid spermatids from diploid spermatocytes. Through the process of spermiogenesis, spermatids undergo maturation and are transformed into functional spermatozoa which are released at spermiation after the breakage of intercellular bridges attaching the spermatids to Sertoli cells [2,3]. Intra-testicular and extra-testicular regulatory hormones involving the release of Follicle Stimulating Hormone (FSH) from pituitary and testosterone from leydig cells are the prime components of a wellorganized spermatogenesis [4]. Sertoli cells control the milieu within the seminiferous tubules in order to facilitate the progression of germ cells to spermatozoa. Hense, spermatogenesis is regulated through the control of FSH on Sertoli cells and LH on Leydig cells. The seminiferous epithelium and hormonal regulation The testis is composed of 400 to 600 ST, which is the functional unit of the test is where 300 million sperms per day are produced after puberty [5]. Sertoli cells have a significant role in supporting the growth of the gonadal cells and thus are known as the ‘nurse’ cells [6]. Leydig cells in return, under the influence of LH, supports the production of testosterone necessarily for the step by step process of Journal of Andrology & Gynaecology Avens Publishing Group Inviting Innovations J Androl Gynaecol October 2019 Vol.:7, Issue:1 © All rights are reserved by Ghina.