DAZL and Azoospermia: In a previous study, our laboratory reported that a co-immunolabeling system with undifferentiated embryonic cell transcription factor 1 (UTF1) and deleted in azoospermia-like (DAZL) could be used to identify undifferentiated (UTF1 only), differentiating (UTF1 and DAZL), or differentiated spermatogonia (DAZL only) [2].