Vasa Gene Developmental Expression Pattern And Gonadal Ontogenesis And Development Of Urechis Unicinctus

The ontogenesis of gonad is a concernful field of developmental biology studies. vasa gene expressed specifically among animal germ line cells, it is widely used as molecular marker of germ cells and play an important role of studies on animal germ cells ontogenesis and reproductive regulation. Since gonad is the place of sexual cells ontogenesis and differentiation, gonad ontogenesis studies could improve reproductive performance of species, enhance germ line characteristics and exploit superior breeding resources. Urechis uniconctus is sole species of Xenopneusta and a kind of unexploited marine animal resources for its higher economic value, medicinal value and potential of coastal environment purification. Current study focuses on Uu-vasa mRNA developmental expression traits of U. uniconctus utilizing In situ hybridization technique; furtherly studing its gonad ontogenesis and developing gonad structure for supplying available research elements of U. uniconctus artificial breeding.According to the results of In situ hybridization, Uu-vasa mRNA possesses similar distribution traits in cells from from unfertilized eggs stage to blastocyst stage, indicating it derives from maternity. At gastrula stage, Uu-vasa mRNA concentrated on endoderm and mesoderm of gastrula. Positive signals focuses on alimentary canal at trochophore stage, body segment membrane and alimentary canal at somite larvae stage, abdominal bristle around and respiratory intestine at worm-like larvae stage. The site positive signals located in respiratory intestine is gonad ontogenesis place in the future.Results of 1～4 cm paraffin slicing of U. uniconctus juveniles indicate PGCs located at connective tissue membrane outside respiratory intestine wall and constitute a gonadal primordium with ambient somatic cells as to 3 cm juveniles. And its initial conformation is similar with that of adult gonad for 4 cm juveniles.Results of adult U. uniconctus paraffin slicing indicate the gonad located at respiratory intestine as thin film shape consisted with germ cells and connective tissue; gonium distributed at gonad external and connective tissue at the middle of gonad; both ends of the gonad connected with respiratory intestine wall exterior and body wall interior through developed fascicles.Based on histological observation results, we devide annual cycle of gonad development of U. uniconctus into five stages:proliferative stage (late Jun.-Jul. and Nov.-Jan.), growing stage (late Jul.-late Aug. and Feb.-early Apr.), ripe stage (late Aug.-middle Sep.and Apr.-early May), spawning stage (late Sep.-middle Oct. and middle May-middle Jun.) and recovery stage (late Oct.-early Nov. and middle Jun.-late Jun.).