Imprint switch mutations at Rasgrf1 support conflict hypothesis of imprinting and define a growth control mechanism upstream of IGF1

Abstract

Rasgrf1 is imprinted and expressed preferentially from the paternal allele in neonatal mouse brain. At weaning, expression becomes biallelic. Using a mouse model, we assayed the effects of perturbing imprinted Rasgrf1 expression in mice with the following imprinted expression patterns: monoallelic paternal (wild type), monoallelic maternal (maternal only), biallelic (both alleles transcribed), and null (neither allele transcribed). All genotypes exhibit biallelic expression around weaning. Consequences of this transient imprinting perturbation are manifested as overall size differences that correspond to the amount of neonatal Rasgrf1 expressed and are persistent, extending into adulthood. Biallelic mice are the largest and overexpress Rasgrf1 relative to wildtype mice, null mice are the smallest and underexpress Rasgrf1 as neonates, and the two monoallelically expressing genotypes are intermediate and indistinguishable from one another, in both size and Rasgrf1 expression level. Importantly, these data support one of the key underlying assumptions of the "conflict hypothesis" that describes the evolution of genomic imprinting in mammals and supposes that equivalent amounts of imprinted gene expression produce equivalent phenotypes, regardless of which parental allele is transcribed. Concordant with the difference in overall body size, we identify differences in IGF-1 levels, both in serum protein and as liver transcript, and identify additional differential expression of components upstream of IGF-1 release in the GH/IGF-1 axis. These data suggest that imprinted Rasgrf1 expression affects GH/IGF-1 axis function, and that the consequences of Rasgrf1 inputs to this axis persist beyond the time period when expression is restricted via epigenetic mechanisms, suggesting that proper neonatal Rasgrf1 expression levels are critical for development.

Detection of a novel single nucleotide polymorphism and imprinted status analysis of the Ras protein-specific guanine nucleotide-releasing factor 1 gene in domestic pigs

“…We found that the Rasgrf1 gene was maternally expressed in the liver and small intestine, paternally expressed in the lung, and biallelically expressed in the brain, heart, spleen, kidney, stomach, pancreas, fat, testis, ovary, longissimus dorsi, and pituitary. These observations are not consistent with those from imprinting reports about the mouse and rat Rasgrf1 gene (Plass et al, 1996;Dockery et al, 2009;Drake et al, 2009). The differential imprinting status of the Rasgrf1 gene among rat, mouse and pig may be caused by the different species or the different tissues that were examined.…”

“…neonatal brain, heart, stomach, and liver (Plass et al, 1996;Dockery et al, 2009). The imprinting of the mouse Rasgrf1 gene in a few tissues is relaxed during development, the transition from strongly and predominantly paternal allelic expression to biallelic expression can be seen over time, and expression becomes biallelic around the time of weaning (Drake et al, 2009). Interestingly, compared to the imprinted expression of the Rasgrf1 gene in mouse and rat, we observed a variance in the imprinting of the Rasgrf1 gene in domestic pigs.…”

A catalogue of validated single nucleotide polymorphisms in bovine orthologs of mammalian imprinted genes and associations with beef production traits

“…For example, studies of the murine RASGRF1 ortholog (Rasgrf1) show that it is predominantly expressed from the paternal allele in neonatal brain tissue, with expression becoming biallelic during weaning and later into adulthood (Plass et al, 1996;Drake et al, 2009). The spatio-temporal expression patterns of this gene have led to suggestions that it may play a role in memory and learning (Giese et al, 2001).…”

“…The spatio-temporal expression patterns of this gene have led to suggestions that it may play a role in memory and learning (Giese et al, 2001). Gene knockout studies have shown that mice strains deficient in Rasgrf1 activity display a moderate reduction in body weight (15% to 30%) compared to wild-type strains, suggesting a role for Rasgrf1 in post-natal growth and development (Giese et al, 2001;Clapcott et al, 2003;Drake et al, 2009). Interestingly, the differential Rasgrf1 gene expression levels in the mice models resulted in concordant differential expression of Igf1 (the insulin-like growth factor 1 gene) and molecular components of the growth hormone/insulin-like growth factor 1 (GH/IGF1) axis, which are essential for normal growth and development (Drake et al, 2009).…”

“…Gene knockout studies have shown that mice strains deficient in Rasgrf1 activity display a moderate reduction in body weight (15% to 30%) compared to wild-type strains, suggesting a role for Rasgrf1 in post-natal growth and development (Giese et al, 2001;Clapcott et al, 2003;Drake et al, 2009). Interestingly, the differential Rasgrf1 gene expression levels in the mice models resulted in concordant differential expression of Igf1 (the insulin-like growth factor 1 gene) and molecular components of the growth hormone/insulin-like growth factor 1 (GH/IGF1) axis, which are essential for normal growth and development (Drake et al, 2009). The data presented in this study suggest that the bovine RASGRF1 ortholog may similarly play an important physiological role in the growth, development, maintenance and performance of beef cattle, possibly through involvement with the GH/IGF1 axis.…”