The SO(H)L(H) "O" drivers of oocyte growth and survival but not meiosis I

Abstract

The spermatogenesis/oogenesis helix-loop-helix (SOHLH) proteins SOHLH1 and SOHLH2 play important roles in male and female reproduction. Although previous studies indicate that these transcriptional regulators are expressed in and have in vivo roles in postnatal ovaries, their expression and function in the embryonic ovary remain largely unknown. Because oocyte differentiation is tightly coupled with the onset of meiosis, it is of significant interest to determine how early oocyte transcription factors regulate these two processes. In this issue of the JCI, Shin and colleagues report that SOHLH1 and SOHLH2 demonstrate distinct expression patterns in the embryonic ovary and interact with each other and other oocyte-specific transcription factors to regulate oocyte differentiation. Interestingly, even though there is a rapid loss of oocytes postnatally in ovaries with combined loss of Sohlh1 and Sohlh2, meiosis is not affected and proceeds normally.

Figure 1. Expression of SOHLH1 and SOHLH2 in a mouse oocyte.

The temporal expression (A) and spatial expression (shown in the cytoplasm or the nucleus in B) of SOHLH1 and SOHLH2 proteins are distinct at different embryonic time points during oocyte development in the mouse ovary. The expression of another oocyte transcription factor, NOBOX, closely overlaps with that of SOHLH1, although its weak expression is noted at early time points (indicated by a question mark above the dashed line in A). Shin et al. demonstrate that SOHLH1 is required for nuclear localization of SOHLH2 in germ cells in the mouse ovary after, but not before, E16.5 (B).