Transgene driving GFP expression from the promoter of the zona pellucida gene zpc is expressed in oocytes and provides an early marker for gonad differentiation in zebrafish.

Although mechanisms of sex differentiation have been studied intensely in mammals, insects, and worms, little is known about this process in lower vertebrates. To establish a marker for female gonad differentiation in zebrafish, we generated a transgenic line in which 412 bp from the promoter and 5' mRNA leader of the female-specific zebrafish zona pellucida gene zpc are fused to the coding region of green fluorescent protein (GFP). The zpc0.5:GFP transgene is expressed exclusively in oocytes, starting from the onset of female-specific differentiation, and closely resembles the expression pattern of the wild-type zpc. Strong GFP expression persists throughout oogenesis and is visible through the body wall of females. We have also characterized a putative upstream factor of zpc, FIGalpha, and show that distribution of FIGalpha RNA is compatible with its postulated role in the regulation of zpc. The zpc0.5:GFP transgenic line described here will be useful for studying oocyte development and the mechanisms that determine sex-specific gene expression in the zebrafish. It is also the first promoter characterized to date to drive stable and efficient expression specifically in the zebrafish female germline. Copyright 2003 Wiley-Liss, Inc.