Limits...
Divergence of imprinted genes during mammalian evolution.

Hutter B, Bieg M, Helms V, Paulsen M - BMC Evol. Biol. (2010)

Bottom Line: Interestingly, we found that the early divergence of imprinted genes was accompanied by an unusually strict conservation of their paralogs.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Lehrstuhl für Computational Biology, Universität des Saarlandes, D-66041 Saarbrücken, Germany.

ABSTRACT

Background: 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. Here, we aimed at assessing the evolutionary history of imprinted genes.

Results: In 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.

Conclusions: The 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.

Show MeSH

Related in: MedlinePlus

Complementary divergence. The orthologs of single copy genes (s) are more diverged than the orthologs of genes that possess paralogs. Regarding paralogous pairs of biallelically expressed genes (b1, b2), one is usually more diverged than the other. If an imprinted gene (a1i) has a paralog (a2), the imprinted gene itself is in most cases the more divergent one.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC2875234&req=5

Figure 2: Complementary divergence. The orthologs of single copy genes (s) are more diverged than the orthologs of genes that possess paralogs. Regarding paralogous pairs of biallelically expressed genes (b1, b2), one is usually more diverged than the other. If an imprinted gene (a1i) has a paralog (a2), the imprinted gene itself is in most cases the more divergent one.

Mentions: Although duplication events might not be directly linked to evolution of imprinted gene regulation, the existence of paralogs may have enabled a greater divergence of imprinted genes by relaxation of purifying selection. Genes that possess paralogs show evolutionary patterns that differ from those of singleton genes [28-30,34]. Notably, there is complementary divergence between pairs of paralogs, where imprinted genes seem to be concentrated in the group of the faster evolving duplicates (Figure 2). The strong conservation of their non-imprinted paralogs suggests that these genes may have compensated for the divergence by maintaining the original functions of the ancestral genes.


Divergence of imprinted genes during mammalian evolution.

Hutter B, Bieg M, Helms V, Paulsen M - BMC Evol. Biol. (2010)

Complementary divergence. The orthologs of single copy genes (s) are more diverged than the orthologs of genes that possess paralogs. Regarding paralogous pairs of biallelically expressed genes (b1, b2), one is usually more diverged than the other. If an imprinted gene (a1i) has a paralog (a2), the imprinted gene itself is in most cases the more divergent one.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2875234&req=5

Figure 2: Complementary divergence. The orthologs of single copy genes (s) are more diverged than the orthologs of genes that possess paralogs. Regarding paralogous pairs of biallelically expressed genes (b1, b2), one is usually more diverged than the other. If an imprinted gene (a1i) has a paralog (a2), the imprinted gene itself is in most cases the more divergent one.
Mentions: Although duplication events might not be directly linked to evolution of imprinted gene regulation, the existence of paralogs may have enabled a greater divergence of imprinted genes by relaxation of purifying selection. Genes that possess paralogs show evolutionary patterns that differ from those of singleton genes [28-30,34]. Notably, there is complementary divergence between pairs of paralogs, where imprinted genes seem to be concentrated in the group of the faster evolving duplicates (Figure 2). The strong conservation of their non-imprinted paralogs suggests that these genes may have compensated for the divergence by maintaining the original functions of the ancestral genes.

Bottom Line: Interestingly, we found that the early divergence of imprinted genes was accompanied by an unusually strict conservation of their paralogs.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Lehrstuhl für Computational Biology, Universität des Saarlandes, D-66041 Saarbrücken, Germany.

ABSTRACT

Background: 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. Here, we aimed at assessing the evolutionary history of imprinted genes.

Results: In 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.

Conclusions: The 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.

Show MeSH
Related in: MedlinePlus