Meeting Abstract

S1.2  Monday, Jan. 4  Evolution of reproductive endocrine system in chordates KUBOKAWA, K*; TANDO, T; Ocean. Res. Inst., Univ. of Tokyo; Ocean. Res. Inst., Univ. of Tokyo kubokawa@ori.u-tokyo.ac.jp

The cephalochordate, amphioxus, is phylogenetically placed at the most primitive position in the chordate clade. Despite many studies on the endocrine system of amphioxus, any definitive evidence has not been reported for the presence of the pituitary-gonadal axis, which is the important endocrine system for the reproduction in vertebrates. Recent genome analyses in amphioxus, Branchiostoma floridae, showed that amphioxus has no pituitary hormones except thyrostimulin (Holland et al., Genome Res 2008). It is a glycoprotein hormone which forms a heterodimer with α and β subunits, and presents in various organs in vertebrates. The analyses of a phylogenetic tree and a synteny suggested that the amphioxus thyrostimulin is the ancient type of glycoprotein hormones in chordates. Furthermore, the sex steroidogenic enzymes, members of CYP enzymes, were found in the genome sequences. The conversion pathway of sex steroids from cholesterol to estrogen and androgen, and the major sex steroids was also identified in gonads of amphioxus, B. belcheri in vitro and in vivo. We cloned the genes coding for amphioxus thyrostimulin and sex steroidogenic enzymes, and confirmed their expression in amphioxus by in situ hybridization technique. On the basis of these findings, we discuss the evolution of hormones and their function in the pituitary-gonadal axis in chordates.