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Show HONORS PROGRAM SPRING 2007 Shannon K. Evans David L. Gard 125 Evolution of Alternative Splicing in the MAP215/DIS1 Family of Microtubule Associated Proteins Shannon K. Evans (David L. Gard) Department of Biology University of Utah XMAP215, the founding member of the MAP215/Dis1 family of microtubule associated proteins, was first identified in the African clawed frog Xenopus laevis. XMAP215 is a novel MAP required for formation of mei-otic spindles in Xenopus oocytes. In vitro, XMAP215 has been found to promote microtubule elongation and dynamics specifically at the plus end. Additionally, XMAP215’s activity has been shown to be regulated by phosphorylation during M-phase in Xenopus oocytes and embryos (Gard and Kirschner, 1987). Two iso-forms of XMAP215 are expressed during Xenopus development. The isoforms are the result of differential splicing, and differ in the presence of a serine and threonine rich sequence of 36 amino acids known as insert 2 (Becker and Gard, 2000). The transcript including the exon encoding insert 2 is expressed in oocytes, eggs, and early embryos, and may be important in regulating the rapid cell cycles of early development in Xenopus. Searches of genome databases revealed that the exon encoding insert 2 is not present in the MAP215 genes of teleost fishes or mammals. A sequence 55% identical and 77% similar to insert 2 has been found in the MAP215 gene of chickens. Based upon these observations, we propose that the insert 2 exon arose in a common ancestor of terrestrial vertebrates and was subsequently lost through deletion or divergence in the MAP215 genes of mammals. This hypothesis was tested by performing sequential RT-PCR and PCR reactions using nested primers to amplify, clone, and sequence cDNAs and genomic sequences spanning the insert 2 exon in MAP215 transcripts and/or genes in a variety of vertebrate species, including: a frog (Rana pipiens), two salamanders (Ambystoma and Nectarus), a toad (Bufo sp.), a lizard (Anolis carolinensis), and garter snake (Thamnophis sp.) (Evans, Sanzenbacher, and Gard, 2006, unpublished observations). |
