Different species have different lifespans. For example, a dwarf goby fish (Eviota sigillata) lives only eight weeks, the Greenland shark lives in contrast for 400 years. Forest shrew lives about two years, and bowhead whales up to 200 years. The average life expectancy of a person today is 79 years, although, some people live much longer. To date, the longest living human officially registered with the Guinness Book of Records is Jeanne Calman who lived 122 years and 164 days.
Why do different species have different life spans? Since species differ in their gene sequence it stands to reason that genetic differences between species might determine the maximal life span of a species. Although environment al conditions and life experiences can expand life span, nevertheless the clear differences in maximal life span still exist between species. For example, no mouse will live for 100 years even at the best optimal conditions, but humans and bowhead wales do. The difference in life span must be therefore genetic. However, it was unknown where this secret of life and death is hiding in the genome. Obviously if we find this gene/genes we might be able to think about strategies to expand our life span. Achieving immortality has been in the hidden dreams of humans for millennia.
The DNA is a language built from 4 chemical letters: A, C, G and T. Early studies demonstrated a strong correlation between the density of the CG sequence of bases or letters in regions of the genome that control gene expression and lifespan. Why would density of CGs be important? This sequence of letters could be chemically modified by proteins in the cell that add a small chemical called a methyl group to Cs in CGs letters. This process is called DNA methylation. DNA methylation is an important “epigenetic” mechanism which is responsible for controlling how our genes function. When C letters in CG sequences get methylated, they can silence a gene. The denser the CG sequence, the chance that all CGs get randomly methylated is lower.
Where are these critical regions in the genome that play a role in controlling our life span?
In a recent study in the journal Scientific Reports Benjamin Mayne et al., have studied 252 animal species with different life expectancies, from 1.1 years at Notobranch Furzer (luchopera fish of the notobranch family) to sea bass, living up to 205 years. The scientists tried to find whether regions with different CG exist in the genomes of these animals that correlate with their life span. The scientists discovered 42 genes that had different CG densities in different species and these differences corresponded to differences in life span. Now we have regions in the genome that are validated by evolution that play a causal role in determining our life span. This has obviously immense implications. Knowing the genes that define life span will help us understand why some individuals live longer than others. DNA methylation could be affected by life experiences. Perhaps different life experiences affect the level of methylation of these genes. Could we examine different combinations of life experiences and identify those that expand our personal life expectancy by changing methylation of these genes? Could we use these genes to define lifestyles and environments that make our lives healthier and longer? Moreover, this study helps us take a deeper look at environmental issues as well as the evolution of living and extinct species and examine what we could do as a species to expand our life expectancy and what to could be done for protection of threatened species and sustainable fisheries.
Reference: A genomic predictor of lifespan in vertebrates https://www.nature.com/articles/s41598-019-54447-w