Continued Investigations of RasGrf1 and Longevity
RasGrf1 is the gene associated with longevity in engineered mice with two female parents, and a deficiency in the gene achieved through other means boosts life span as well. Here is more theorizing on what it all means: "Interestingly, RasGrf1 is one of parentally imprinted genes transcribed from paternally-derived chromosome. Erasure of its imprinting results in RasGrf1 downregulation and has been demonstrated in a population of pluripotent adult tissues-derived very small embryonic like stem cells (VSELs), stem cells involved in tissue organ rejuvenation. ... downregulation of RasGrf1 in VSELs [protects] from premature depletion from adult tissues. Thus, the studies in RasGrf1-/- mice indicate that some of the imprinted genes may play a role in ontogenetic longevity and suggest that there are sex differences in life span that originate at the genome level. All this in toto supports a concept that the sperm genome may have a detrimental effect on longevity in mammals." So in summary, one of the ways in which RasGrf1 extends life seems to involve improvement in the capacity of stem cells in the older organism, and a significant effect on longevity can emerge from the contributions of one parent through the epigenetic imprinting process.