Stimulated by retinoic acid gene 8 (STRA8) interacts with the germ cell specific bHLH factor SOHLH1 and represses c‐KIT expression in vitro

Maria Giovanna Desimio,Eleonora Cesari,Massimo De Felici,Donatella Farini,Maria Sorrenti

doi:10.1111/jcmm.16087

Abstract

STRA8 (Stimulated by Retinoic Acid Gene 8) controls the crucial decision of germ cells to engage meiotic division up and down‐regulating genes involved in the meiotic programme. It has been proven as an amplifier of genes involved in cell cycle control and chromosome events, however, how STRA8 functions as negative regulator are not well understood. In this study, we demonstrate that STRA8 can interact with itself and with other basic Helix‐Loop‐Helix (bHLH) transcription factors through its HLH domain and that this domain is important for its ability to negatively interfere with the Ebox‐mediated transcriptional activity of bHLH transcription factors. Significantly, we show that STRA8 interacts with TCF3/E47, a class I bHLH transcription factors, and with SOHLH1, a gonadal‐specific bHLH, in male germ cells obtained from prepuberal mouse testis. We demonstrated that STRA8, indirectly, is able to exert a negative control on the SOHLH1‐dependent stimulation of c‐KIT expression in late differentiating spermatogonia and preleptotene spermatocytes. Although part of this results were obtained only ‘in vitro’, they support the notion that STRA8 interacting with different transcription factors, besides its established role as ‘amplifier’ of meiotic programme, is able to finely modulate the balance between spermatogonia proliferation, differentiation and acquisition of meiotic competence.

Highlights

Retinoic Acid (ATRA) has been shown to regulate several biological processes, in particular during embryonic development in mammals.[1]
In the mouse embryonal ovary and preleptotene spermatocytes a complex transcriptional programme of meiosis beginning regulated by STIMULATED BY RETINOIC ACID GENE 8 (STRA8) has been recently revealed.[13,14,37]
The most part of involved genes appear to be engaged in cell cycle regulation, double strand break repair and chromosome synapsis and most of them are expressed before the beginning of the meiotic prophase 1

Summary

| INTRODUCTION

Retinoic Acid (ATRA) has been shown to regulate several biological processes, in particular during embryonic development in mammals.[1]. Both MEIOSIN and STRA8 possesses a conserved region of the protein containing a Helix-Loop-Helix (HLH) domain This is a homo- or hetero-dimerization domain that characterizes the large family of HLH transcription factors and consists of highly conserved amphipathic helices separated by a loop of variable length and sequence.[17] HLH proteins, through the regulation of gene expression, orchestrate cell cycle, cell lineage commitment and cell differentiation.[18] Different groups of HLH proteins can be distinguished based on the presence or absence of additional functional domains.[17,18] Almost all HLH proteins possess a region of basic residues adjacent to the HLH domain that facilitates binding to DNA at a specific sequence motif known as EBox (CANNTG) or at the related NBox (CACNAG).[17] X-ray crystallographic analyses of bHLH proteins have defined the invariant basic sequence ERXR as the determinant for EBox recognition.[19] Class I bHLH factors, known as E proteins, are encoded by Tcf3/Tcfe2a (E12, E47), Tcf[4] and Tcf[12] (HEB) genes. We aimed to characterize the action of STRA8 as a transcriptional regulator and to investigate whether its HLH domain, by mediating the interaction with others HLH protein/s including the germ cell specific bHLH factor SOHLH1 could modulate their transcriptional function

| MATERIALS AND METHODS

Findings

| DISCUSSION