The efficiency of spermatogenesis and the support capacity of Sertoli cells in Characiformes

Abstract

This stereological analysis of the types of germ cells and the number of Sertoli cells per cyst in Astyanax altiparanae testes during spermatogenesis is the first such report in Characiformes. Testes of 25 male A. altiparanae were examined. Based on the number of spermatogonia B per cyst (469.2 ± 9.92), we estimated that spermatogonia undergo at least nine mitotic divisions before differentiating into primary spermatocytes. There are four spermatogonia types: undifferentiated spermatogonia A*, undifferentiated spermatogonia, differentiated spermatogonia, and type B spermatogonia. The number of Sertoli cells increased gradually from 1.41 ± 0.51 in the single undifferentiated spermatogonium A* to 9.25 ± 0.50 in cysts of spermatocytes in the leptotene/zygotene stage, possibly related to greater complexity of cellular events during the meiotic stage. The number of germ cells rose dramatically from spermatogonia A (1.0 ± 0) to spermatogonia B (469.2 ± 9.92); however, the quantity of spermatocytes inside the cysts in the leptotene/zygotene stage decreased (300.6 ± 6.97) relative to spermatogonia B, representing a loss of approximately 36% of the former number of cells. This was probably the result of apoptosis, which promotes successful development of the remaining cells during sperm production. The support capacity of Sertoli cells increased gradually during spermatogenesis.

Stereological analysis of spermatogenesis in Brycon orbignyanus (Characiformes: Bryconidae)

“…At this stage, stereological counts are performed using L/Z and P cysts. An increase germ cells between cysts has only been observed in the species Oreochromis niloticus (Vilela et al, 2003), while in B. orbignyanus , Astyanax lacustris (= A. altiparanae ) (Quirino et al, 2020; Rodrigues et al, 2017) and D. rerio (Leal et al, 2009) cell loss is observed.…”

“…Owing to the increase in germinal cysts during spermatogenesis, there is a significant increase in the number of Sertoli cells, indicating that Sertoli cells are another important factor in the success of spermatogenesis (De Rooji & Russell, 2000). Sertoli cells are attached to germinal cysts, delimiting them and thus limiting the number of germ cells present in the cyst (Rodrigues et al, 2017). In addition to being responsible for nutrition, they also provide hormonal support (synthesizing steroids, follicle‐stimulating hormone and testosterone; Ando et al, 2000; Schulz et al, 2005) and phagocytization of residues (Bizzoto & Godinho, 2007), this increase was evident across species.…”

“…The number of Sertoli cells per cyst increases progressively during spermatogenesis, stopping only in spermiogenesis (intermediate spermatid). However, in O. niloticus (Vilela et al, 2003) and Astyanax lacustris (= A. altiparanae ) (Rodrigues et al, 2017), the number of Sertoli cells also progressively increased; however, their increase ceased in the spermatocyte stage, showing a drop in spermiogenesis.…”

“…Present in the light of the seminiferous tubule, they are already fully formed, presenting a dense nucleus. They have a nuclear diameter of 1.5 ± 0.12 μm (Figure 2i) with approximately nine spermatogonial generations (Rodrigues et al, 2017), unlike that observed in the Characiform Hoplias malabaricus (Bizzoto & Godinho, 2007) and the Cypriniform species Danio rerio and Cyprinus carpio (Vigoya, 2016), which were estimated to have eight spermatogonial generations. It is not possible to determine whether spermatogonial generations are related to species order, indicating that this number is species-specific (Honji et al, 2020).…”

“…An underutilized method for the evaluation of spermatogenesis in fish is stereological analysis, a method that allows quantitative results to be obtained from systematic, uniform and random samples, which can then be applied to any structure in which morphometric study is possible (Leal et al, 2009). This technique allows for a better understanding of the dynamics between the number of germ cells and the number of Sertoli cells, as well as the cellular mechanisms involved in mitosis, meiosisr and cell kinetics (Rodrigues et al, 2017).…”