(A) Addition of dorsomorphin significantly (p<0.001) increased the growth of spermatogonia maintained in culture for 6 weeks. (B) Merged bright field and UV photomicrographs showing a colony containing more than 100 DsRed-expressing spermatogonia. (C) RT-PCR analysis of RNA isolated from spermatogonia maintained for 6-weeks in culture in the presence of dorsomorphin, whole testis tissue and feeder cells alone showing expression of germ cell specific marker genes, dazl, dnd, nanos3, vasa and piwil1 and spermatogonial markers plzf and sox17. RT: reverse transcription; Data points not sharing a letter (A, B, C, D) are significantly different by Bonferroni–Dunn tests. Scale bar = 20 µm.