Transgenerational transmission of environmental information (in the nematode)

Every trait (phenotype) reflects the contribution of one or a few or many hundred or thousands of genes (DNA sequence; our genome), plus epigenetic effects (our ~200 epigenomes that can differ in each of our ~200 different cell types), and environmental insults that occur by the minute, day, month and year. Epigenetics is classically divided now into: DNA methylations, RNA-interference (RNAi), histone modifications, and chromatin remodeling.

Another subdivision of epigenetics is transgenerational inheritance (i.e. studies have shown the diet or stress of a pregnant mother can affect that child’s propensity to obesity or type-2 diabetes later in life; diethylstilbestrol given during the first trimester of a pregnant woman can affect risk of a particular type of vaginal cancer in the child, or even grandchild, later in life; cigarettes smoked by grandparents can affect a grandchild’s predisposition to asthma; etc.). Female rats –– three generations removed from exposure to the endocrine-disruptor (antiandrogenic fungicide vinclozolin) –– discriminate and prefer males who do not have a history of exposure, whereas similarly epigenetically imprinted males do not show such a preference.

Thus, the environment experienced by an animal can sometimes influence gene expression for one or several subsequent generations. In the attached article, authors observed (in the flatworm, Caenorhabditis elegans) that a temperature-induced change in expression of a heterochromatic gene array can endure for at least 14 generations. This inheritance appears to be primarily in cis with (i.e. close by) the DNA locus, occurs through both oocytes and sperm, and is associated with altered trimethylation of histone H3 lysine 9 (H3K9me3) –– before the onset of zygotic transcription (one-cell fertilized egg). Expression profiling revealed that temperature-induced expression from endogenous repressed repeats can also be inherited for multiple generations. Long-lasting epigenetic memory of environmental change is therefore possible, at least in this species of animal.

So many things in molecular biology and genetics that are found in one “lower” species (e.g. worm, yeast, fly) are later realized to have been conserved for many hundreds of millions of years. A great example is the CDKs. These are a family of five mammalian protein kinases, known for participation in regulating the cell cycle; they also participate in transcriptional regulation, mRNA-processing, and differentiation during neurogenesis. CDKs are so highly conserved that yeast cells can divide normally when the human homologue is replaced with the yeast Cdk gene product.

So –– if the finding of a transgenerational transmission of “something” for FOURTEEN generations (in the nematode) is eventually discovered to be true also for Homo sapiens –– then it could be concluded that environmental effects (diet, climate, stress) on our ancesters living during the last half of the 17th century are carried over and still exist in our chromosomes today..!!

Science   21 April 2o17; 356: 320–323

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