Parent-of-origin specific QTL – a possibility towards understanding reciprocal effects in chicken and the origin of imprinting

Abstract

Reciprocal effects for sexual maturity, egg production, egg quality traits and viability are well known in poultry crosses. They have been used in an optimal way to form profitable production hybrids. These effects have been hypothesized to originate from sex-linked genes, maternal effects or a combination of both. However, these may not be the only explanations for reciprocal effects. Recent mapping of quantitative trait loci (QTL) has revealed autosomal areas with parent-of-origin specific effects in the chicken. In mammals, parental imprinting, i.e. the specifically regulated expression of either maternal or paternal allele in the offspring, is the main cause of such effects. The most commonly accepted hypothesis for the origin of imprinting, the conflict hypothesis, assumes a genetic conflict of interest between the maternal and paternal genomes regarding the allocation of resources to the offspring. It also intrinsically implies that imprinting should not occur in oviparous taxa. However, new molecular genetic information has raised a need to review the possible involvement of imprinting or some related phenomena as a putative cause of reciprocal effects in poultry. Comparative mapping provides strong evidence for the conservation of orthologous imprinted gene clusters on chicken macrochromosomes. Furthermore, these gene clusters exhibit asynchronous DNA replication, an epigenetic mark specific for all imprinted regions. It has been proposed that these intrinsic chromosomal properties have been important for the evolution of imprinted gene expression in the mammalian lineage. Many of the mapped parent-of-origin specific QTL effects in chicken locate in or close to these conserved regions that show some of the basic features involved in monoallelic expression. If monoallelic expression in these regions would be observed in birds, the actual mechanism and cause may be different from the imprinting that evolved later in the mammalian lineage. In this review we discuss recent molecular genetic results that may provide tools for understanding of reciprocal differences in poultry breeding and the evolution of imprinting.

Rapid evolution of osmoregulatory function by modification of gene transcription in steelhead trout

“…The non-additive effects we identified at CFTR I and GHRII are curious, since the reciprocal crosses differ substantially. Classically, reciprocal cross divergence is explained by sex-linkage or extra-nuclear inheritance, although sex-linked epistatic effects or maternal imprinting are also possible explanations (Falconer and Mackay 1996;Tuiskula-Haavisto and Vilkki 2007). There is no evidence for sex-linkage or extra-nuclear inheritance of the genes assayed here, thus sex-linked epistatic effects or genetic CFTR I NaKa GHRII NaKb β-actin IgM CFTR I NaKa GHRII NaKb β-actin * * * * * Fig.…”

Quantitative trait loci associated with fatness in a broiler–layer cross

“…However, studies have raised a need to review the possible involvement of imprinting or some related mechanism as a putative cause of reciprocal effects in chickens (Abasht et al. 2006; Tuiskula‐Haavisto & Vilkki 2007). Hager et al.…”

Microsatellite mapping of QTLs affecting resistance to coccidiosis (Eimeria tenella) in a Fayoumi × White Leghorn cross

“…Here, both QTL on GGA1 and GGA3 might not explain all this observed difference and, moreover, shown effects of opposite directions. In most cases, the reciprocal effects showed are likely a combination of both maternal effects and parent of origin effects [ 32 ]. There is growing evidence of the importance of parent of origin effect as a source of genetic variation in other species, like in sheep [ 33 ] and more examples are likely to come for disease resistance related traits.…”