Expression pattern of foxl2 and dmrt1 in gonad of Amur sturgeon Acipenser schrenckii in relation to sex differentiation

Abstract

The mechanisms that govern sex differentiation in sturgeon are poorly understood. This study aimed to examine sexual dimorphic expression of foxl2 and dmrt1 in Amur sturgeon Acipenser schrenckii during molecular and morphological sex differentiation. Histologically, ovaries were first observed at 9months after hatching (mah), reflected in an invaginated gonadal epithelium and the presence of germ cells just below the epithelium, whereas gonads with smooth epithelium and germ cells in the stroma were characterized as testis. Some fish showed undifferentiated gonads until 16mah, but all sampled fish had morphologically differentiated sex by 19mah. The full-length cDNAs of foxl2 and two types of dmrt1, dmrt1a and dmrt1b, of Amur sturgeon were isolated. The 2 types of dmrt1 cDNA had an identical structure from the 5′-UTR to the Y-rich domain, whereas the sequence downstream from this domain showed no homology and is considered to have resulted from alternative splicing. Foxl2 was principally expressed in the ovary and the 2 types of dmrt1 in the testis of 7-year-old Amur sturgeon, and much less so in various somatic tissues. Foxl2 expression was sexually dimorphic in morphologically differentiated gonads and was similarly dichotomous in the undifferentiated gonads of fish at 9mah. In contrast, sexually dimorphic expression of dmrt1a and dmrt1b was not observed in gonads of the juvenile Amur sturgeon, but these genes showed testis-dominant expression in the adults. We suggest that foxl2 expression is closely related to ovarian differentiation and that two types of dmrt1 play a role in testis development and/or sperm formation rather than testicular differentiation. Additionally, we suggest that mRNA levels of foxl2 are an appropriate marker for sexing of sturgeon at an early developmental stage.