Molecular identification and expression of FOXL2 and DMRT1 genes from willow minnow Gnathopogon caerulescens

Willow minnow, Gnathopogon caerulescens, is a commercially important freshwater fish species in Japan. In particular, female fish with eggs are more expensive than male fish. Many methods have been tested to achieve 100% willow minnow female production; however, none of them were successful because of the temperature-dependent sex determination mechanism. To date, the molecular mechanism underlying sex determination in willow minnow is still not completely understood. This study was designed as an attempt to understand the sex differentiation mechanism of willow minnow at the molecular level. We cloned the mRNAs of two sex-related genes of G. caerulescens-forkhead-box protein L2 (FOXL2) and doublesex- and mab-3-related transcription factor 1 (DMRT1). We compared the inferred amino acid sequences to those of other fish and examined the expression patterns of these genes in adult tissues and during development. The FOXL2 and DMRT1 genes of willow minnow were isolated and identified. Both gene sequences share high homology with those of Chinese Cyprinidae. The cell- and tissue-specific expression of FOXL2 and DMRT1 were also determined. Both genes were expressed in gonads, and their expression level increased before gonadal sex differentiation. Overall, these results suggest that these two genes play a key role in the sex differentiation of willow minnow. Detailed knowledge regarding this mechanism will be useful for efficient all-female cyprinid fish production that follows a temperature-dependent sex determination system.