Among mammalian species, moms can have it rough. THEY do the foraging and the child rearing usually without the help of dad who may or may not be prancing about defending his territory or doing who knows what. The biological systems that manage such a predicament for the female would, not surprisingly, be highly regulated and, I imagine, a major target of natural selection. For example, conflicts between what’s best for the offspring and what’s best for mom could drive the evolution of genetic and epigenetic mechanisms that counter-balance the tendency of moms to conserve resources and for offspring to use resources. One such epigenetic mechamism that has been implicated in parent-offspring conflict is so-called genomic imprinting – wherein certain epigenetic marks (methylation of C*pG’s in many cases) leads to the expression of genes a parent-of-origin-type manner (eg. the gene inherited from mom might be expressed while the gene inherited from dad would be transcriptionally repressed).
With this link between epigenetics and maternal investment in mind (and with Mother’s Day around the corner) I enjoyed the recent paper, “Lasting Epigenetic Influence of Early-Life Adversity on the BDNF Gene” by Roth and colleagues [doi: 10.1016/j.biopsych.2008.11.028] where they measured the relationship between BDNF expression and methylation as a function of maternal behavior (in stressful and non-stressful) conditions. Like many other neuronally-expressed genes, stress seems to lead to more methylation, which can – sometimes – interfere with transcription. In the Roth et al., paper, BDNF seems to show this pattern as well since BDNF was downregulated about 50% in the prefrontal cortex of rat pups who were reared under stressful conditions. Concomitant increases in methylation in the pups (which was blocked with methyltransferase inhibitors) was examined as a possible reason for the BDNF downregulation. Most interestingly, the female pups who were raised by stressed moms – were themselves lousy moms (demonstrated poor licking and grooming behavior) and gave birth to pups (granddaughters) who also bore similar epigenetic marks on BDNF.
Is this maternal-care/epigenetics phenomena related to parent-offspring conflict? Perhaps so, or perhaps just a spandrel or an unintended consequence of other levels of regulation. It will be fun to explore this further. Until then – be sure to thank your GRANDmother on Mother’s Day! – or not, if your are poorly groomed.