In Search of the Genetics of Longevity in Sea Urchins

Comparative biology is an important tool in aging research, as the analysis of similar species with widely divergent life spans can in theory point out the more important mechanisms of aging. The more similar the species the better, and so here researchers investigate the genetics of two sea urchin species that exhibit a twenty-fold difference in life span. This is a preliminary set of data, absent any rigorous analysis, but even at the outset it doesn't exactly fit the expected picture. There is no real reason to expect a universality of relative importance of mechanisms across diverse species, so things that have proved to be important in well-studied species such as flies, mice, and people may well turn out to have little relevance to more distant branches of the tree of life. As a general rule, we should always expect biology to be more complex and varied rather than less so:

Sea urchins have attracted attention due to the extreme longevity of some of their species. Red sea urchin, S. franciscanus, populating cold waters of Pacific coast of North America, was demonstrated to survive over a century. Although S. franciscanus could not be cultivated in the lab for a century for direct observation, deposition pattern of radioactive carbon released to the Pacific upon nuclear tests and skeleton growth rate studies using tetracycline labeling allowed red sea urchin to climb the pedestal of the most long-lived marine animals. At the same time, green sea urchin, L. variegatus, populating warm Caribbean sea hardly survive over four years. Although direct difference in the senescence rates between red and green sea urchins is hard to demonstrate directly on the sole basis of field studies, these two related species might be the a convenient pair for comparative genetics of longevity. In this report we aimed to obtain draft genome assemblies of S. franciscanus and L. variegatus and compare the sequence of their proteins related to longevity with longevity related proteins of other species.

Analysis revealed several aminoacid positions that co-vary with longevity. Although this approach is not guaranteed from mistakes originated from misalignment, identification of related proteins that have different function, it could present a framework of further hypothesis-driven experiments on longevity. Our analysis revealed highly uneven distribution of proteins having aminoacid residues that co-vary with longevity among functional categories. Surprisingly, several categories of proteins were completely devoid of such positions. For example, nuclear encoded mitochondrial proteins and proteins involved in reactive oxygen species inactivation. Minimum of such aminoacids were found in the components of insulin/IGF1 pathway. Particularly enriched in positions that vary in coordination with longevity are categories of mitochondrial proteins encoded in mitochondrial genome, lipid transport proteins, proteins involved in amyloidogenesis and system of telomere maintenance. Among other, catalytic subunit of telomerase, telomerase reverse transcriptase (TERT) holds absolute record of the frequency of such positions. Despite the fact, that somatic telomerase activity could be detected in short and long living sea urchins, TERT might be involved in longevity due to more intricate mechanisms, such as maintaining the balance between support of tissue renovation and simultaneous restriction of unwanted proliferation of cancerous cells.



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