Meeting Abstract

54.2  Jan. 6  Evolution of Vertebrate Striated Myosins: Myosin Heavy Chain Diversity in Amphioxus SCHACHAT, F.; Duke Univ. Med. Ctr. f.schachat@cellbio.duke.edu

The position of cephalochordates in vertebrate phylogeny is controversial (Gee, 1996; Delsuc et al., 2006). Nonetheless, whether cephalochordates are the most basal of living chordates or a sister phyla of chordates, they remain an important organism in which to explore early events in the evolution of chordate characters. These studies focus on one such character, striated muscle specialization, defined by myosin heavy chain diversity and patterns of expression. They suggest that celphalochordates are more primitive than tunicates, and that cephalochordate striated muscle exhibits highly derived, as well as primitive, characters. RNA from Branchiostoma floridae was amplified using RT-PCR with primers that span a region of the myosin head containing several key functional elements. Six distinct cDNA sequences were identified. The Branchiostoma trace sequence archive at GenBank was used to further analyze these coding sequences, and the genes that generate them. Their expression in notochordal, myomeric, ventral, velar and pharyngeal muscle was also investigated. One of the myosins is predominant in notochordal muscle, which expresses paramyosin and has filaments as long as 30 microns. Three of the myosins are present in myomeric and ventral muscles, which have vertebrate cross-striated character. Another sequence is restricted to the head region, and it is the only myosin that has known homologs in contemporary vertebrates. Interestingly the last myosin sequence is more closely related to smooth and nonmuscle myosins than to striated myosins.