HUSSAIN, SM; LIVINGSTON, BT; Univ of South FL; Univ of South FL: Variation of a protien coding microsatellite Between and Within species of Strongylocentrotus

To better understand the evolution of repetitive regions and microsatellites within coding sequences, we have been studying the echinoderm SM50 gene, which encodes a protein involved in skeleton formation. Through the use of Dot Plots and sequence alignments we have analyzed the repeat region of SM50 in individuals from various species in the Strongylocentrotus clade. We found that almost every repeat in Strongylocentrotus purpuratus differs by at least one base pair while other members of the Strongylocentrotus clade exhibit much more similarity between each repeat than previously predicted. We have also discovered new types of repeats within SM50 in species previously not reported. Based on the types of substitution patterns observed in the repetitive region of SM50, we have made predictions about how the process of concerted evolution might be influenced. We tested these predictions by sequencing many individuals from representative species. S. purp shows no variation within the large repeat region. In contrast two closely related species, S. droebachiensis and S. pallidus, do show variation in the number of long repeats contained within the gene. The changes in the repeats within each species are consistent with what we had predicted based on substitution patterns. In addition, analysis of both the repeat region and the non-repetitive region of this gene supports recent relationships of the species and supports the idea of two populations of S. drob on either side of the Atlantic Ocean.