Allelic expression of mammalian imprinted genes in a matrotrophic lizard, Pseudemoia entrecasteauxii
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Genomic imprinting is a process that results in the differential expression of genes depending on their parent of origin. It occurs in both plants and live-bearing mammals, with imprinted genes typically regulating the ability of an embryo to manipulate the maternal provision of nutrients. Genomic imprinting increases the potential for selection to act separately on paternally and maternally expressed genes, which increases the number of opportunities that selection can facilitate embryonic control over maternal nutrient provision. By looking for imprinting in an independent matrotrophic lineage, the viviparous lizard Pseudemoia entrecasteauxii (Scincidae), we test the hypothesis that genomic imprinting facilitates the evolution of substantial placental nutrient transport to embryos (matrotrophy). We sequenced transcriptomes from the embryonic component of lizard placentae to determine whether there are parent-of-origin differences in expression of genes that are imprinted in mammals. Of these genes, 19 had sufficiently high expression in the lizard to identify polymorphisms in transcribed sequences. We identified bi-allelic expression in 17 genes (including insulin-like growth factor 2), indicating that neither allele was imprinted. These data suggest that either genomic imprinting has not evolved in this matrotrophic skink or, if it has, it has evolved in different genes to mammals. We outline how these hypotheses can be tested. This study highlights important differences between mammalian and reptile pregnancy and the absence of any shared imprinting genes reflects fundamental differences in the way that pregnancy has evolved in these two lineages.
KeywordsViviparity Parent-offspring conflict Pseudemoia Placenta Placentotrophy Lizard Scincidae Genomic imprinting
Lizards were collected under New South Wales National Parks and Wildlife Licence to MBT (SL100401). We thank Intersect Australia Ltd. for supercomputing resources as well as Bosch MBF and M. Olsson for laboratory resources. This project was supported by The Australian Society of Herpetologist’s student research grant and the Gaylord Donnelley Postdoctoral Environmental Fellowship to OWG, Australian Research Council Discovery Early Career Research Award to MCB (DE120101615), and ARC Discovery Project funding to MBT (DP120100649).
OWG performed pyrosequencing, data analyses, and wrote the manuscript. OWG and MCB collected lizards and constructed RNA-seq libraries. MBT, MCB, KB, and OWG contributed to development of the ideas and conclusions, experimental design, and editing of the manuscript.
Compliance with ethical standards
Animal work was conducted under University of 441 Sydney Animal Ethic approval.
Conflict of interest
The authors declare that they have no conflict of interest.
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