Transcriptional Similarity in Couples Reveals the Impact of Shared Environment and Lifestyle on Gene Regulation through Modified Cytosines

TL;DR

This study reveals that couples share similar gene expression patterns influenced by shared environment, with cytosine modifications playing a mediating role, highlighting non-genetic factors in gene regulation.

Contribution

It demonstrates that shared environment affects gene regulation in couples through cytosine modifications, a novel insight into non-genetic influences on gene expression.

Findings

778 genes show reduced variance in couples

Shared environment influences gene regulation via cytosine modifications

Transcriptional similarity partly mediated by CpG site modifications

Abstract

Gene expression is a complex and quantitative trait that is influenced by both genetic and non-genetic regulators including environmental factors. Evaluating the contribution of environment to gene expression regulation and identifying which genes are more likely to be influenced by environmental factors are important for understanding human complex traits. We hypothesize that by living together as couples, there can be commonly co-regulated genes that may reflect the shared living environment (e.g., diet, indoor air pollutants, behavioral lifestyle). The lymphoblastoid cell lines (LCLs) derived from unrelated couples of African ancestry (YRI, Yoruba people from Ibadan, Nigeria) from the International HapMap Project provided a unique model for us to characterize gene expression pattern in couples by comparing gene expression levels between husbands and wives. Strikingly, 778 genes were found to show much smaller variances in couples than random pairs of individuals at a false discovery rate (FDR) of 5%. Since genetic variation between unrelated family members in a general population is expected to be the same assuming a random-mating society, non-genetic factors (e.g., epigenetic systems) are more likely to be the mediators for the observed transcriptional similarity in couples. We thus evaluated the contribution of modified cytosines to those genes showing transcriptional similarity in couples as well as the relationships these CpG sites with other gene regulatory elements, such as transcription factor binding sites (TFBS). Our findings suggested that transcriptional similarity in couples likely reflected shared common environment partially mediated through cytosine modifications.