Embryonic expression of medaka Ol-bsf and correlated expression dynamics together with dmrt1bY during gonadal primordium formation.

(A to R) Medaka Ol-bsf expression investigated by fluorescence using a transgenic reporter line for which a 732-bp Ol-bsf promoter fragment (up to the next upstream gene) drives the expression of the mCherry. Medaka Ol-vas and dmrt1bY expressions were investigated by fluorescence using previously described transgenic reporter lines ([11] and [61], respectively). (A) During neurulation (stages 16/17), Ol-bsf is ubiquitously expressed. (A insert) Cytoplasmic localisation of Ol-bsf after transient transfection of a 3-times FLAG version of Ol-bsf in a medaka embryonic stem cell line and immunohistochemistry. (B to P) From stage 25 on, Ol-bsf expression is restricted to the germ cells and colocalize with the germ cell marker Ol-vas. (K to P) Four-dph expression of Ol-bsf is apparently heterogeneous within the population of PGCs while dmrt1bY is now expressed in the surrounding somatic cells of the primordial gonad (K to M). (Q and R) By stage 29, Ol-bsf and dmrt1bY are both expressed in the germ cells. Variations within the respective levels of Ol-bsf and dmrt1bY are clearly observable amongst different germ cells although always correlated between the 2 fluorescences (curly brackets compared to square brackets). dph, days post hatching; MES-1, medaka embryonic stem cells; Ol-BSF, Oryzias latipes Bicoid Stability Factor; olf1, Oryzias latipes fibroblast-1; PGC, primordial germ cell.