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Review
. 2019 Sep 6;7:186.
doi: 10.3389/fcell.2019.00186. eCollection 2019.

Sexual Dimorphism in the Age of Genomics: How, When, Where

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Free PMC article
Review

Sexual Dimorphism in the Age of Genomics: How, When, Where

Daniel F Deegan et al. Front Cell Dev Biol. .
Free PMC article

Abstract

In mammals, sex chromosomes start to program autosomal gene expression and epigenetic patterns very soon after fertilization. Yet whether the resulting sex differences are perpetuated throughout development and how they connect to the sex-specific expression patterns in adult tissues is not known. There is a dearth of information on the timing and continuity of sex biases during development. It is also unclear whether sex-specific selection operates during embryogenesis. On the other hand, there is mounting evidence that all adult tissues exhibit sex-specific expression patterns, some of which are independent of hormonal influence and due to intrinsic regulatory effects of the sex chromosome constitution. There are many diseases with origins during embryogenesis that also exhibit sex biases. Epigenetics has provided us with viable mechanisms to explain how the genome stores the memory of developmental events. We propose that some of these marks can be traced back to the sex chromosomes, which interact with the autosomes and establish sex-specific epigenetic features soon after fertilization. Sex-biased epigenetic marks that linger after reprograming may reveal themselves at the transcriptional level at later developmental stages and possibly, throughout the lifespan. Detailed molecular information on the ontogeny of sex biases would also elucidate the sex-specific selective pressures operating on embryos and how compensatory mechanisms evolved to resolve sexual conflict.

Keywords: embryogenesis; epigenetics; sex-biased expression; sexual dimorphism; transcriptional regulation.

Figures

FIGURE 1
FIGURE 1
Sex-specific transcriptional networks and phenotype maps. Schematic representation of the relationships between genotype, transcriptional networks, and final phenotype during development. Male and female genotypes, represented as XY and XX produce distinct epigenotypes, with effects on and counter-effects from the autosomes (A). Modifications of the epigenotype on the autosomes lead to transcriptional changes that in turn influence expression from the sex chromosomes. Different transcription factor (TF) networks can either determine distinct phenotypes (space A) or converge to an equivalent phenotype (spaces B, C).
FIGURE 2
FIGURE 2
Schematic of our hypothesis. (A) Sex biases have different origins depending on the developmental stage of the organism. Before gonadogenesis, sex chromosomes are the primary determinants of sex differences. Sex hormones influence the transcriptome and epigenome independently of and in combination with sex chromosome effects. (B) Soon after fertilization, male and female cells have sex-specific transcriptomes, epigenomes, and phenotypes (for example, male embryos grow faster than female embryos). At implantation, lineage determination begins and gene expression differences are reduced. Epigenetic marks, however, are less constrained and some are maintained, affecting gene expression, and phenotype later in development. Once specific lineages are established, differences in gene expression increase again due to environmental, hormonal and genetic factors, some of which act on sex-specific epigenetic features established prior to differentiation.

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References

    1. Arnold A. P. (2012). The end of gonad-centric sex determination in mammals. Trends Genet. 28 55–61. 10.1016/j.tig.2011.10.004 - DOI - PMC - PubMed
    1. Arnold A. P. (2014). Conceptual frameworks and mouse models for studying sex differences in physiology and disease: why compensation changes the game. Exp. Neurol. 259 2–9. 10.1016/j.expneurol.2014.01.021 - DOI - PMC - PubMed
    1. Arnold A. P. (2019). Rethinking sex determination of non-gonadal tissues. Curr. Top. Dev. Biol. 134 289–315. 10.1016/bs.ctdb.2019.01.003 - DOI - PubMed
    1. Arnold A. P., Chen X., Itoh Y. (2012). What a difference an X or Y makes: sex chromosomes, gene dose, and epigenetics in sexual differentiation. Handb. Exp. Pharmacol. 214 67–88. 10.1007/978-3-642-30726-3_4 - DOI - PMC - PubMed
    1. Arnold A. P., van Nas A., Lusis A. J. (2009). Systems biology asks new questions about sex differences. Trends Endocrinol. Metab. 20 471–476. 10.1016/j.tem.2009.06.007 - DOI - PMC - PubMed

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