Resequencing of the TMF-1 (TATA Element Modulatory Factor) regulated protein (TRNP1) gene in domestic and wild canids

Cortical folding is related to the functional organization of the brain. The TMF-1 regulated protein (TRNP1) regulates the expansion and folding of the mammalian cerebral cortex, a process that may have been accelerated by the domestication of dogs. The objectives of this study were to sequence the TRNP1 gene in dogs and related canid species, provide evidence of its expression in dog brain and compare the genetic variation within dogs and across the Canidae. The gene was located in silico to dog chromosome 2. The sequence was experimentally confirmed by amplifying and sequencing the TRNP1 exonic and promoter regions in 72 canids (36 purebred dogs, 20 Gy wolves and wolf-dog hybrids, 10 coyotes, 5 red foxes and 1 Gy fox).

A partial TRNP1 transcript was isolated from several regions in the dog brain. Thirty genetic polymorphisms were found in the Canis sp. with 17 common to both dogs and wolves, and only one unique to dogs. Seven polymorphisms were observed only in coyotes. An additional 9 variants were seen in red foxes. Dogs were the least genetically diverse. Several polymorphisms in the promoter and 3'untranslated region were predicted to alter TRNP1 function by interfering with the binding of transcriptional repressors and miRNAs expressed in neural precursors. A c.259_264 deletion variant that encodes a polyalanine expansion was polymorphic in all species studied except for dogs. A stretch of 15 nucleotides that is found in other mammalian sequences (corresponding to 5 amino acids located between Pro58 and Ala59 in the putative dog protein) was absent from the TRNP1 sequences of all 5 canid species sequenced. Both of these aforementioned coding sequence variations were predicted to affect the formation of alpha helices in the disordered region of the TRNP1 protein.

Potentially functionally important polymorphisms in the TRNP1 gene are found within and across various Canis species as well as the red fox, and unique differences in protein structure have evolved and been conserved in the Canidae compared to all other mammalian species.