Fig. 7.

Model for hub cell specification in the male gonad. (A) SGPs (brown) become Notch-activated as they passively travel by Delta-expressing PMG cells (dark blue) during germ band retraction. (B) During early gonad coalescence as germ cells (yellow) and SGPs form a contiguous tissue, SGPs begin to differentiate into either hub (green) or cyst cells (purple). (C) During late gonad coalescence, Notch-activated hub cells must migrate towards the anterior. Sox100B-positive male-specific SGPs (light blue) join the gonad. (D) During the last stage of embryogenesis, stage 17, the niche cells execute a mesenchymal-to-epithelial transition, upregulate cell-adhesion molecules and induce Unpaired expression, establishing germline stem cells (GSCs, red).