Cloning and expression of the zebrafish germ cell nuclear factor

Nuclear orphan receptors are DNA-binding proteins that share the domain str ucture of the nuclear hormone receptor superfamily, although their ligands are unknown. Members of the nuclear receptor family are involved in the reg ulation of various developmental and reproductive processes. We have identi fied such a nuclear orphan receptor in the zebrafish and named it zebrafish germ cell nuclear factor (zfGCNF) based on its high sequence homology to p reviously described mouse, human, and Xenopus laevis GCNF. Detailed sequenc e comparison of zfGCNF with mouse, human, and frog GCNF revealed high homol ogies in the domains conserved in the nuclear receptor family. Homology in the DNA-binding domain is 97% for frog and even 98.5% for mouse and human w hen compared to the zebrafish sequence. Homology in the E III subdomain of the tuansactivation/ligand-binding E domain is 100% when compared to the mo use and human sequences. Transcripts of different size were detected by Nor thern blot analysis in the zebrafish ovary, whereas, in the testis only one transcript was present. In situ hybridization revealed that zfGCNF was pre dominantly expressed in previtellogenic oocytes in the ovary and in spermat ocytes in the testis. (C) 1999 Wiley-Liss, Inc.