Maternal age elicits phenotypic variation in the Caenorhabditis elegans (nematode)

For years, on these pages of “Gene-Environment Interactions,” we’ve pointed out that the genotype [dependent on: DNA alterations (i.e. genetics), epigenetic changes (i.e. DNA-methylation, RNA-interference, histone modifications, chromatin remodeling), adverse environmental effects, and even obscure (poorly understood) transgenerational effects] reflects the ultimate phenotype (trait) that is seen. This can be a Mendelian trait involving just a few “large-effect” genes, or a multifactorial trait involving hundreds or thousands of genes, most of which have small-effect. Interestingly, the topic of this publication [attached] involves “maternal age” as an (unexpected?) factor that contributes to phenotypic variation. (Albeit the animal model system being studied here is the (lowly) tiny roundworm, Caenorhabditis elegans, which is about 1-mm in length.)

Genetically identical individuals that grow in the same environment often show substantial phenotypic variation within populations of organisms –– as diverse as bacteria, invertebrates such as flies and worms, and vertebrates such as fish, frogs, rodents and humans. With some exceptions, the causes are poorly understood. Authors [see attached report] show that isogenic (“presumed to be genetically identical”) Caenorhabditis elegans nematodes vary in their size at hatching, speed of development, rate of growth, starvation resistance, fecundity (rate of fertility), and also in the rate of development of their germline (development of sperm and ova) relative to that of somatic tissues. These six underlined characteristics in this paragraph can all be defined as traits (phenotypes).

Authors demonstrated that the primary cause of this variation is the age of each individual nematode’s mother –– with the progeny of young mothers exhibiting several phenotypic impairments. They identified age-dependent changes in maternal provisioning of the lipoprotein complex vitellogenin to embryos as the pivotal molecular mechanism that underlies the variation in multiple traits throughout the life of an animal. Authors suggest (but I’m not so sure about it) that production of sub-optimal progeny by young mothers might reflect a trade-off between the competing fitness traits of “a short generation-time” and the “survival and fecundity” of the progeny.

Nature 7 Dec 2o17; 552: 106–109

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