Sox9b/sox9a2‐EGFP transgenic medaka reveals the morphological reorganization of the gonads and a common precursor of both the female and male supporting cells

Abstract

We have established an enhanced green fluorescent protein (EGFP) transgenic medaka line that mimics the expression of sox9b/ sox9a2 to analyze the morphological reorganization of the gonads and characterize the sox9b-expressing cells during gonadal formation in this fish. After the germ cells have migrated into the gonadal areas, a cluster of EGFP-expressing cells in the single gonadal primordium was found to be separated by the somatic cells along the rostrocaudal axis and form the bilateral lobes. We observed in these transgenic fish that EGFP expression persists only in the somatic cells directly surrounding the germ cells. As sex differentiation proceeds, dmrt1 and foxl2 begin to be expressed in the EGFP-expressing cells in the XY and the XX gonads, respectively. This indicates that the sox9b-expressing cells reorganize into two lobes of the gonad and then differentiate into Sertoli or granulosa cells, as common precursors of the supporting cells. Hence, our sox9b-EGFP medaka system will be useful in future studies of gonadal development. Mol. Reprod.

Two distinct types of theca cells in the medaka gonad: Germ cell‐dependent maintenance of cyp19a1‐expressing theca cells

“…In addition to the ventral cells, the posterior portions of the gonad at 10 dph and the entire region of the gonad at 20 dph showed EGFP expression in the follicular cells that surround the oocytes (Fig. 1F,H, white arrowheads; Nakamura et al, 2008a). At 20 dph, EGFP expression was observed in the entire region of the developing gonads, consistent with the folliculogenesis throughout the gonad.…”

“…At 10 dph, some populations of cyp19a1-expressing cells were observed on the ventral side of the stromal region, as demonstrated in Figure 1. The other population was located in the outer layer of follicles and adjacent to the foxl2-expressing granulosa cells, suggesting that these cells are not the supporting cells surrounding germ cells which have been identified previously in vertebrates (e.g., Nakamura et al, 2008a).…”

“…The extension of the right lobe always precedes that of the left lobe in the OK-Cab medaka strain ( Fig. 1C; Nakamura et al, 2008a). By 20 dph, the EGFP expression became uniform throughout the developing female gonad (Fig.…”

“…Interestingly, the expression expands anteriorly as the gonad extends toward the rostral region (Fig. 1A,C,E; Nakamura et al, 2008a). The extension of the right lobe always precedes that of the left lobe in the OK-Cab medaka strain ( Fig.…”

“…It has previously been reported that granulosa cells express foxl2 (Nakamoto et al, 2006;Nakamura et al, 2008a), whereas theca cells express P450c17-I (cyp17a1; Kobayashi et al, 1996;Kurokawa et al, 2007;Zhou et al, 2007a,b). To understand the type of cyp19a1-expressing cells present in the developing gonad and the adult ovary, immunohistochemistry (EGFP) coupled to in situ hybridization (foxl2 and P450c17-I) was performed using the cyp19a1-EGFP transgenic medaka ( Fig.…”