Spinyhead Croaker Germ Cells Gene dnd Visualizes Primordial Germ Cells in Medaka

Spinyhead croaker (Collichthys lucidus) is an economically important fish suffering from population decline caused by overfishing and habitat destruction. Researches on the development of primordial germ cell (PGC) and reproduction biology were an emergency for the long-term conservation of the involved species. Dead end (dnd) gene plays an indispensable role in PGC specification, maintenance, and development. In the current study, we report the cloning and expression patterns of dnd in C. lucidus (Cldnd). RT-PCR analysis revealed that Cldnd was specifically expressed in both sexual gonads. In the ovary, Cldnd RNA was uniformly distributed in the oocytes and abundant in oogonia, and gradually decreased with oogenesis. A similar expression pattern was also detected in testis. Dual fluorescent in situ hybridization of Cldnd and Clvasa demonstrated that they almost had the same distribution except in oocytes at stage I, in which the vasa RNA aggregated into some particles. Furthermore, Cldnd 3' UTR was sufficient to guide the Green Fluorescent Protein (GFP) specifically and stably expressed in the PGCs of medaka. These findings offer insight into that Cldnd is an evolutionarily conserved germline-specific gene and even a potential candidate for PGC manipulation in C. lucidus.