Identification of type A spermatogonia in turbot (Scophthalmus maximus) using a new cell-surface marker of Lymphocyte antigen 75 (ly75/CD205)

Turbot (Schophthalmus maximus) is one of the most important economic marine flatfish species. However, due to rapid development of the industry, genetic resource recession has brought down the efficiency of aquaculture. Therefore, conservation of the genetic resource is increasingly demanded. Recent research proved that type A spermatogonia possesses the properties of spermatogonia stem cell, and it might provide an ideal solution. Therefore, it is necessary to develop an appropriate molecular marker on type A spermatogonia to further isolate and purify of type A spermatogonia in turbot. In this study, turbot lymphocyte antigen 75 (smly75) gene was identified and its localizations of expressions and the temporal transcription patterns were evaluated qualitatively and semiquantitatively. Investigation in testes of development of spermatogonia showed that smly75 mRNA, contrast with vasa and dnd mRNA, was exclusively localized in type A spermatogonia and not detected in type B spermatogonia, spermatocytes or gonadal somatic cells by in situ hybridization. Thus, the smly75 could be a new and convincing molecular marker on identification of type A spermatogonia. In addition, specifically to development pattern of type A spermatogonia, from 7- to 14- month testes, spermatogonia were dominated and the number of type A spermatogonia was increased, corresponding that smly75 expression was up-regulated gradually, while, in 16 month testes, accompanied by that several spermatogonia differentiated into primary spermatocytes, the smly75 expression down-regulated. Finally, broaden in the whole reproductive cycle, the smly75 transcription significantly variated with the differentiation of germ cells and in accordance with the number of type A spermatogonia. It is suggested that testes from 8 to 14 month old males could be used for further isolation and purification of type A-SG. These results will not only help to better understand type A spermatogonia, but also further facilitate type A spematogonia-mediated germ cell manipulation in turbot.