Regionally distinct patterns of STAT3 phosphorylation in the seminiferous epithelia of mouse testes

Abstract

In mouse testes, Sertoli cells support the continuous process of spermatogenesis, which is dependent on seminiferous epithelial cycles along the longitudinal axis of the seminiferous tubule. Sertoli cell function is modulated partly by local cytokines and/or growth factors derived from adjacent tissues such as blood vessels, macrophages, rete testis, etc. However, the spatial activation patterns by local signals in vivo remain unclear. In this study, we focused on Signal Transducers and Activators of Transcription (STAT) signaling in Sertoli cells, because STAT is a major crucial cytokine transducer for somatic cyst cell regulation in Drosophila testis niches. In mouse testes, STAT3 was ubiquitously expressed in Sertoli cells throughout the seminiferous tubules. Phosphorylated STAT3 (p-STAT3) was predominantly observed in the Sertoli cells within the valve-like structure adjacent to the rete testis (i.e., the Sertoli valve [SV]) in the terminal segment of the proximal seminiferous tubules. In the distal seminiferous tubules with active spermatogenesis, most Sertoli cells were negative for anti-p-STAT3 staining. Albeit rarely, a small patch of several p-STAT3-positive Sertoli cells was detected frequently in seminiferous epithelial cycle stages I-VI. Such p-STAT3-positive ratios in the convoluted seminiferous epithelia were significantly increased in germ cell-less testes than in the wild-type testes, but with considerably lower ratios than in the SV region. These findings imply that regionally distinct patterns of STAT3 phosphorylation in the Sertoli cells depend on either location or spermatogenic activity in normal healthy testes in vivo, highlighting a novel entry point to understanding STAT signaling in mammalian spermatogenesis.

The rete testis harbors Sertoli-like cells capable of expressing DMRT1

“…CDH1 is a component of adherens junctions prominently expressed in epithelial tissues (Schneider & Kolligs 2015). The previous study (Nagasawa et al 2018) and our current findings demonstrated that the only somatic cells expressing CDH1 in the mouse testis were epithelial cells of the rete testis. The third marker examined, KRT8, in pair with KRT18, forms intermediate filaments in many simple epithelia (Owens & Lane 2003).…”

“…We also performed immunofluorescent staining for acetylated alpha-tubulin (ace-TUB), which has been reported to be a marker of SCs from the transitional zones (Nagasawa et al 2018). At 1 day of culture, most Figure 2 Characterization of adult and immature SLCs.…”

The Rete Testis: Development and Role in Testis Function

“…In contrast to TZ SCs, AKT activity in the SCs of the seminiferous tubules changes cyclically, achieving a maximum at stages II-VI of the spermatogenic epithelial cycle and a minimum at stages IX-XII. Thus, phosphorylated (p-AKT) is a molecular marker of the TZ region, as is the phosphorylated signal transducer and activator of transcription 3 (p-STAT3, Nagasawa et al, 2018) reported previously.…”

JAK/STAT signaling in stem cells and regeneration: fromDrosophilato vertebrates

“…Furthermore, although transient-amplifying spermatogonia in the mouse testis can fragment and contribute to the spermatogonial stem cell pool (Nakagawa et al, 2010), whether JAK/STAT signaling is involved in this process during homeostasis or stress is not known. It has been shown that activated Stat3 in the mouse testis is concentrated in somatic Sertoli cells that support undifferentiated spermatogonial cells, consistent with the expression pattern of activated Stat92E in the Drosophila testis (Nagasawa et al, 2018). What activates Stat3 and its specific roles in Sertoli cells are not entirely clear.…”