Meeting Abstract
P3.141 Jan. 6 Existence of sex steroids in ovary of amphioxus, Branchiostoma belcheri KUBOKAWA, Kaoru*; MIZUTA, Takanobu; ORI, Unv of Tokyo, Japan; ORI, Unv of Tokyo, Japan kubokawa@ori.u-tokyo.ac.jp
The amphioxus, cephalochordate is the closest living invertebrate relative of vertebrates, and study of amphioxus genes would provide important information on the evolutionary linkage between invertebrate to vertebrate. Morphology and developmental biology on amphioxus have been extensively studied, but limited information has been available on physiology and endocrinology. Evolution of the endocrine control to reproduction is unrevealed in amphioxus although spawning patterns were well studied (Mizuta and Kubokawa, 2004). We attempted EST analysis to obtain genes expressed in the nerve cord of amphioxus to discuss the evolutionary origin of reproductive function. We attempted to survey the precursor genes encoding peptide and protein hormones, and their receptors by using EST method. The cDNA library was conducted from nerve codes of fifty hundred adult amphioxi. The sequences of 5� regions of 7,863 clones were searched on the BLAST database. From EST clones, highly homologous genes to neuropeptides, sex steroids metabolizing enzymes are selected and determined their sequences. The enzymes are cytochrome P450 enzymes which metabolize sex steroids in the synthesis pathway from cholesterol to various sex steroids. In ovary, progesterone, estrogen and androgen are detected by using the radioimmunoassay method established in vertebrates. Cytochrome P450 enzymes exist through all vertebrates but not in invertebrate. The genome sequences were reported in tunicate, which belongs to chordate and considered to be evolutionary lower than amphioxus, but no sex steroid metabolizing enzyme genes have been detected in the genome. It is suggested the amphioxus is the only invertebrate use sex steroids for its reproduction. Mizuta, T., and K. Kubokawa (2004). J Exp Mar Bio Eco. 309: 239-251.
