Dazl and dnd Identify Both Embryonic and Gonadal Germ Cells in Chinese Hook Snout Carp (Opsariichthys bidens)

In recent years, the Chinese hook snout carp (Opsariichthys bidens) is becoming increasingly popular due to its high nutritional value and delicious taste. However, anthropogenic influences have caused a rapid reduction in its population. Considering long-term development sustainability, it is essential to conduct research on its reproductive development. In this study, the germ-cell related genes dazl (Obdazl) and dnd (Obdnd) were cloned, and their expression patterns were revealed. RT-PCR analysis indicated that Obdazl and Obdnd were specifically expressed in gonads. In the testis, Obdazl and Obdnd RNAs have a similar expression pattern: their transcripts were abundant in spermatogonia, gradually decreased, and eventually disappeared during spermatogenesis. Early oocytes in the ovary exhibited strong expression of Obdazl and Obdnd RNAs and reduced remarkably after peak expression at III oocytes. Surprisingly, Obdazl RNA was dynamically found in perinuclear spots that finally aggregated into the Balbiani body (Bb) in the early oocytes. Moreover, Obdazl 3′ UTR enabled the reporter gene to be expressed stably in medaka PGCs, suggesting that dazl was identified as the germ cell marker in O. bidens, which may provide perspectives for further studies on the development of PGCs in the future.