Evolution of the Arginine vasopressin receptor 1A (avpr1a) and its pseudogene in the genus Microtus
A. Berrio, J.L. Pino, S.M. Phelps. 2011. Cis-regulatory evolution of the avpr1a locus and its pseudogene among New World voles. Program No. 186.09. 2011 Neuroscience Meeting Planner. Washington, DC: Society for Neuroscience.
ABSTRACT: Gene duplication is a common process with profound consequences for the function and evolution of a locus. Once a gene has been duplicated, either copy can be lost or can assume a new function, and it is necessary to examine both copies across related species to make correct inferences about the evolution of the locus. Voles are increasingly important models for the molecular mechanisms of social behavior. The evolution of avpr1a locus, which codes for the vasopressin 1a receptor, has been a major focus of this work. The avpr1a locus has undergone a duplication thought to be unique to the socially monogamous prairie voles, Microtus ochrogaster. However, the locus and its duplicate have not been systematically investigated across Microtus species. To do so, we PCR-amplified the 1100 bp of cis-regulatory sequence of the avpr1a locus and its putative pseudogene, as well sequence from two neutral loci (LCAT introns 2-4 and exons 3-5, ~700bp; b-fibrinogen intron 7, ~700bp) from 7 species of New World Microtus with well-characterized mating systems: M. ochrogaster, M. pinetorum, M. agrestis, M. arvalis, M. californicus, M. pennsylvanicus and M. richardsonii. The first 2 species are socially monogamous, and the remaining 5 are all promiscuous. We first used Bayesian methods to reconstruct a phylogeny for these species based on neutral markers, using Myodes glareolus as an outgroup. The phylogenetic analysis gave substantially higher resolution than has been previously reported. Remarkably, this included a strongly supported pairing of the two monogamous species, M. ochrogaster and M. pinetorum (posterior probability = 0.99), which suggests that monogamy may have evolved a single time within this clade. This is a novel pairing, but accords with historic groupings based on tooth structure. Preliminary analysis suggests the avpr1a amplicons were more closely related to one another than to the pseudogene amplicons, which would indicate that the duplication of the locus predated diversification of the clade. Together, our data highlight how phylogenetic analyses can inform our understanding of the evolution of genes regulating social behavior and other complex phenotypes.
A. Berrio, N.S. Lysak, D.V. Blondel, J.L. Pino, S.M. Phelps. 2010. Evolution of cis-regulatory variation at the avpr1a locus and its pseudogene. Program No. 387.12. 2010 Neuroscience Meeting Planner. San Diego, CA: Society for Neuroscience.
ABSTRACT: Individual and species differences in gene expression underlie a tremendous diversity of behavior. Expression of the vasopressin 1a receptor (V1aR), for example, governs behavioral differences between the monogamous prairie vole (Microtus ochrogaster) and the promiscuous montane vole (M. montanus). Field data demonstrate that natural selection favors pair-bonding by male prairie voles; such selection may promote uniformly high levels of V1aR in the ventral pallidum (VPal), a region central to male pairing. In contrast, field data suggest selection actively maintains variation in the retrosplenial cortex (RSctx), a region implicated in spatial memory, territorial intrusions and sexual infidelity. Differences in gene expression are often due to variation in cis-regulatory sequences; alternatively, duplicated loci can also function as regulators of the original locus. We examined the evolution of cis-regulatory sequences of the prairie and montane vole avpr1a loci, as well as an avpr1a-pseudogene thought to be unique to prairie voles. We first tested for evidence of selection acting on the prairie vole avpr1a. To do so, we sequenced 20 avpr1a alleles from wild-caught prairie voles for ~2.5kb upstream of the translation start site, and homologous sequence from the montane vole. We compared the ratio of between- and within-species nucleotide polymorphisms at the avpr1a locus (36:18) with that at neutral loci (21:20). We found a trend toward reduced polymorphism at the prairie vole avpr1a (p<0.10), suggesting overall purifying selection at the locus. A single 50bp region seems to have been under stronger purifying selection than the locus as a whole (p<0.05), and much stronger selection than is evident for neutral loci (p<0.01). This is consistent with the fitness value of V1aR-mediated pair-bonding, and suggests a novel enhancer for high pallidal V1aR. A 300bp segment exhibited a trend toward higher levels of standing variation (p=0.11), a signature of balancing selection. Remarkably, this same segment contained SNPs associated with individual differences in RSctx V1aR. Lastly, we sequenced 20 alleles of the pseudogene to determine whether its cis-regulatory sequences have been under selection since divergence from the avpr1a locus. We found much lower standing variation (between:within, 19:1) than predicted based on neutral loci (21:20), indicating strong purifying selection on the pseudogene cis-regulatory region (p<0.001). Together, our data suggest novel regulators of avpr1a expression, including the possible involvement of a pseudogene previously assumed to be non-functional.
ABSTRACT: Gene duplication is a common process with profound consequences for the function and evolution of a locus. Once a gene has been duplicated, either copy can be lost or can assume a new function, and it is necessary to examine both copies across related species to make correct inferences about the evolution of the locus. Voles are increasingly important models for the molecular mechanisms of social behavior. The evolution of avpr1a locus, which codes for the vasopressin 1a receptor, has been a major focus of this work. The avpr1a locus has undergone a duplication thought to be unique to the socially monogamous prairie voles, Microtus ochrogaster. However, the locus and its duplicate have not been systematically investigated across Microtus species. To do so, we PCR-amplified the 1100 bp of cis-regulatory sequence of the avpr1a locus and its putative pseudogene, as well sequence from two neutral loci (LCAT introns 2-4 and exons 3-5, ~700bp; b-fibrinogen intron 7, ~700bp) from 7 species of New World Microtus with well-characterized mating systems: M. ochrogaster, M. pinetorum, M. agrestis, M. arvalis, M. californicus, M. pennsylvanicus and M. richardsonii. The first 2 species are socially monogamous, and the remaining 5 are all promiscuous. We first used Bayesian methods to reconstruct a phylogeny for these species based on neutral markers, using Myodes glareolus as an outgroup. The phylogenetic analysis gave substantially higher resolution than has been previously reported. Remarkably, this included a strongly supported pairing of the two monogamous species, M. ochrogaster and M. pinetorum (posterior probability = 0.99), which suggests that monogamy may have evolved a single time within this clade. This is a novel pairing, but accords with historic groupings based on tooth structure. Preliminary analysis suggests the avpr1a amplicons were more closely related to one another than to the pseudogene amplicons, which would indicate that the duplication of the locus predated diversification of the clade. Together, our data highlight how phylogenetic analyses can inform our understanding of the evolution of genes regulating social behavior and other complex phenotypes.
A. Berrio, N.S. Lysak, D.V. Blondel, J.L. Pino, S.M. Phelps. 2010. Evolution of cis-regulatory variation at the avpr1a locus and its pseudogene. Program No. 387.12. 2010 Neuroscience Meeting Planner. San Diego, CA: Society for Neuroscience.
ABSTRACT: Individual and species differences in gene expression underlie a tremendous diversity of behavior. Expression of the vasopressin 1a receptor (V1aR), for example, governs behavioral differences between the monogamous prairie vole (Microtus ochrogaster) and the promiscuous montane vole (M. montanus). Field data demonstrate that natural selection favors pair-bonding by male prairie voles; such selection may promote uniformly high levels of V1aR in the ventral pallidum (VPal), a region central to male pairing. In contrast, field data suggest selection actively maintains variation in the retrosplenial cortex (RSctx), a region implicated in spatial memory, territorial intrusions and sexual infidelity. Differences in gene expression are often due to variation in cis-regulatory sequences; alternatively, duplicated loci can also function as regulators of the original locus. We examined the evolution of cis-regulatory sequences of the prairie and montane vole avpr1a loci, as well as an avpr1a-pseudogene thought to be unique to prairie voles. We first tested for evidence of selection acting on the prairie vole avpr1a. To do so, we sequenced 20 avpr1a alleles from wild-caught prairie voles for ~2.5kb upstream of the translation start site, and homologous sequence from the montane vole. We compared the ratio of between- and within-species nucleotide polymorphisms at the avpr1a locus (36:18) with that at neutral loci (21:20). We found a trend toward reduced polymorphism at the prairie vole avpr1a (p<0.10), suggesting overall purifying selection at the locus. A single 50bp region seems to have been under stronger purifying selection than the locus as a whole (p<0.05), and much stronger selection than is evident for neutral loci (p<0.01). This is consistent with the fitness value of V1aR-mediated pair-bonding, and suggests a novel enhancer for high pallidal V1aR. A 300bp segment exhibited a trend toward higher levels of standing variation (p=0.11), a signature of balancing selection. Remarkably, this same segment contained SNPs associated with individual differences in RSctx V1aR. Lastly, we sequenced 20 alleles of the pseudogene to determine whether its cis-regulatory sequences have been under selection since divergence from the avpr1a locus. We found much lower standing variation (between:within, 19:1) than predicted based on neutral loci (21:20), indicating strong purifying selection on the pseudogene cis-regulatory region (p<0.001). Together, our data suggest novel regulators of avpr1a expression, including the possible involvement of a pseudogene previously assumed to be non-functional.