Abstract
BackgroundIn contrast to the majority of mammalian genes, imprinted genes are monoallelically expressed with the choice of the active allele depending on its parental origin. Due to their special inheritance patterns, maternally and paternally expressed genes might be under different evolutionary pressure. Here, we aimed at assessing the evolutionary history of imprinted genes.ResultsIn this study, we investigated the conservation of imprinted genes in vertebrate genomes and their exposition to natural selection. In a genome-wide comparison, orthologs of imprinted genes show a stronger divergence on cDNA and protein level in mammals. This pattern is most pronounced for maternally expressed genes in rodents in comparison to their non-rodent orthologs. The divergence is not attributable to increased mutation of CpG positions. It is contrasted by strong conservation of paternally expressed genes in mouse and rat. Interestingly, we found that the early divergence of imprinted genes was accompanied by an unusually strict conservation of their paralogs.ConclusionsThe apparent degeneration of maternally expressed genes may reflect a relaxation of selective pressure due to counteracting effects on maternal and embryonic fitness. Functional redundancy provided by the presence of highly conserved (non-imprinted) paralogs may have facilitated the divergence. Moreover, intensification of imprinting in modern rodents seems to have shifted the evolutionary fate of imprinted genes towards strong purifying selection.
Highlights
In contrast to the majority of mammalian genes, imprinted genes are monoallelically expressed with the choice of the active allele depending on its parental origin
Expressed genes show reduced conservation In order to assess the evolutionary conservation of imprinted genes, we selected 58 pairs of orthologous protein encoding human and mouse genes for which imprinting has been reported in at least one of the two species in the Otago Catalogue of Imprinted Genes [12,13] and in the literature. These imprinted genes were compared on a genome-wide scale to all genes annotated in the HomoloGene database [14]. This database provides information derived from alignments of orthologous RefSeq cDNA and protein sequences
Compared to genome-wide data, human and mouse ortholog pairs of maternally expressed genes are less conserved in terms of cDNA identity (p < 0.05) and the encoded proteins show a trend towards reduced identity (p < 0.06; Table 1, data for individual imprinted genes are given in additional file 1)
Summary
In contrast to the majority of mammalian genes, imprinted genes are monoallelically expressed with the choice of the active allele depending on its parental origin. Due to their special inheritance patterns, maternally and paternally expressed genes might be under different evolutionary pressure. A number of genes do not obey this rule, notably socalled imprinted genes They acquire specific epigenetic marks in the parental germ lines which are the cause of monoallelic expression after fertilization. It depends on the parental origin which allele of an imprinted gene gets inactivated. Based on the finding that genomic imprinting is a specific feature of species in which embryo and mother are in direct contact to each
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
