Access Type

Open Access Dissertation

Date of Award

December 2011

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Biological Sciences

First Advisor

Mark F. VanBerkum

Abstract

G protein-coupled receptors (GPCRs) are one of the largest class of transmembrane signaling proteins that regulate essential developmental and physiological processes in a cell. GPCR success is illustrated by their abundance across both invertebrate and vertebrate genomes. Phylogenetic analyses show that GPCR families have undergone a lot of gene gain and loss during insect evolution. In Drosophila melanogaster, the fifteen Methuselah/Methuselah-like (Mth/Mthl) genes are in fact an insect specific family of GPCRs. In our study, we conducted a phylogenetic analysis using receptor sequences from five Drosophila species and two related insects, including Tribolium and Anopheles to examine the evolution of this gene family. Clearly Mthl1, 5, and 14 form their own separate clades. The remaining Drosophila genes along with a single gene in Tribolium form a fourth clade defined by the presence of the Mth ectodomain. Expression patterns of the Tribolium gene and all Drosophila paralogs were determined by in situ hybridization. The Tribolium Mthl gene is expressed in the hindgut and mesodermal crystal cells of the embryo which is divided between Drosophila Mthl9 and Mthl10. Mthl10 also evolves other more specific expression patterns in both the embryo third instar larvae which is divided between the other Mthl genes. In summary, six genes (Mthl 1, 5, 9, 11, 13 and 14) are expressed in the embryo, four (Mthl3, 4, 6 and 8) in the larval CNS and imaginal discs and two (Mthl10 and Mth) in both embryos and larvae. We further show Mthl5 expression in the cardiac mesoderm of stage 11 embryos and later restricted to cardioblast cells of the aorta. Loss of mthl5 decreases pericardial-cardial cell association necessary to maintain cardiac intergrity. We show that mthl5 genetically interacts with Goa to increase the loss of cell-cell adhesion in the Drosophila aorta. Together these data clearly show the expansion of the Mth/Mthl family in insects and the evolution of novel gene functions required for organ morphogenesis.

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