Meeting Abstract

S1.6  Monday, Jan. 4  Genomics of Amphioxus and Tunicates: Tracing the Evolution of the Endocrine System SHERWOOD, Nancy/M*; ROCH, Graeme/J; TELLO, Javier/A; University of Victoria; University of Victoria; University of Victoria nsherwoo@uvic.ca

The sequencing of the genomes for amphioxus and tunicates has allowed us to examine the foundation of the endocrine system in species that evolved at the transition between invertebrates and vertebrates. In regard to reproduction, the neuroendocrine system in these early chordates is vertebrate-like, but the pituitary and gonadal endocrine hormones and receptors are clearly lacking a number of vertebrate components. In tunicates (Ciona intestinalis and C. savignyi), six gonadotropin-releasing hormones (GnRH) and four receptors were cloned. The six GnRH peptides selectively activated recombinant forms of their receptors and in vivo spawning. In amphioxus (Brachiostoma floridae), four GnRH receptors were cloned and expressed in COS7 cells; their pattern of response provides evidence that both invertebrate-type and vertebrate-type GnRH receptors exist in amphioxus. In contrast, functioning neuroendocrine systems in basal chordates do not appear to activate specific pituitary hormones, as neither FSH nor LH hormones/receptors are identified in the amphioxus or tunicate genomes. Rather it is likely that the GnRH peptides act directly on the gonads. Only amphioxus and not Ciona has the necessary enzymes for biosynthesis of sex steroids. Also, both chordate groups have a small number of nuclear receptors but only amphioxus has steroid-type nuclear receptors. Outside of reproduction, the insulin-IGF family and receptors, essential for growth, development and metabolism, are present in both amphioxus and tunicates along with other hormones including the osmoregulatory hormone stanniocalcin. The endocrine components are homologous to those in vertebrates and reveal the foundation of the chordate endocrine system before the genomic duplications in early vertebrates.