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Summary A previous study revealed a strong association between the DMRT3:Ser301STOP mutation in horses and alternate gaits as well as performance in harness racing. Several follow-up studies have confirmed a high frequency of the mutation in gaited horse breeds and an effect on gait quality. The aim of this study was to determine when and where the mutation arose, to identify additional potential causal mutations and to determine the coalescence time for contemporary haplotypes carrying the stop mutation. We utilized sequences from 89 horses representing 26 breeds to identify 102 SNPs encompassing the DMRT3 gene that are in strong linkage disequilibrium with the stop mutation. These 102 SNPs were genotyped in an additional 382 horses representing 72 breeds, and we identified 14 unique haplotypes. The results provided conclusive evidence that DMRT3:Ser301STOP is causal, as no other sequence polymorphisms showed an equally strong association to locomotion traits. The low sequence diversity among mutant chromosomes demonstrated that they must have diverged from a common ancestral sequence within the last 10 000 years. Thus, the mutation occurred either just before domestication or more likely some time after domestication and then spread across the world as a result of selection on locomotion traits.

Transmembrane proteins are gatekeepers of the cells; controlling the transport of substrates as well as communicating signals among cells and between the organelles and cytosol. Solute carriers (SLC) and G protein-coupled receptors (GPCR) are the largest family of membrane transporters and membrane receptors respectively. The overall aim of this thesis was to provide a basic understanding of some of the novel SLCs and GPCRs with emphasis on expression, transport property, evolution and probable function. The first part of the thesis directs towards the study of some novel solute carriers. In an initial study, we provided an overall picture of the sequence relationship and tissue expression of 14 diverse atypical SLCs confirming some of their evolutionary conservation and highly specific expression pattern. The focus then was on the SLC17 family (mainly vesicular proteins) and a novel member named Slc17a9. This study revealed that SLC17 family could be divided into four main phylogenetic clades which were all present before the divergence of the insect lineage with Slc17a9 having the most restricted evolutionary history. Detailed expression study of Slc17a9 in the mouse brain suggests that it is also expressed in some regions important for purinergic neurotransmission. Further, we deorphanised an aminoacid transporter Slc38a7 which was expressed in a majority of neurons in the CNS and showed that it preferably mediate transport of L–glutamine and L–histidine. The second part of the thesis focuses on the study of two GPCRs belonging to the Rhodopsin superfamily, Gpr162 and Gpr153. A phylogenetic analysis revealed that both Gpr153 and Gpr162 originated from a common ancestor before the radiation of the mammalian lineage. Expression study revealed that Gpr162 had a predominant expression in the CNS and relatively lower expression in the other tissue tested whereas Gpr153 had a more widespread and similar expression pattern in both CNS and peripheral tissues. The functional studies of the two GPCRs were done using the antisense oligodeoxynucleotide knockdown rat model. These studies provided evidence linking the orphan Gpr162 gene with the regulation of food intake– related behaviour whereas Gpr153 gene caused only a slight reduction in food intake.