Essential genes are often thought to be frozen in evolutionary time-evolving only very slowly because their changing or elimination would lead to the organism's death. Hundreds of millions of years of evolution separate insects and mammals, but experiments show that the Hox genes guiding the development of the body plans in Drosophila fruit flies and mice can be swapped without a hitch because they are so similar. This remarkable evolutionary conservation is a foundational concept in genome research. But a new study turns this rationale for genetic conservation on its head.
Rapidly changing heterochromatin drives the evolution of new essential genes. Young genes are just as likely as old ones to encode essential functions. The most rapidly evolving ones were much more likely to encode essential functions than the more slowly evolving ones. These transcription factors did not localize to euchromatin, the part of the genome where most genes are located, but in the heterochromatin — the regions of densely packed DNA that are mainly kept in a silent state because they contain most of the noncoding DNA and other so-called genomic junk.
Genes commonly evolve by duplication and divergence. A study examined the role of relatively abundant and functionally important de novo genes. These are newly evolved genes, without a possible parent gene. Under the right environmental conditions, stretches of DNA, without any function can provide some advantages, and thus start evolving under selection. Scientists found that overexpressing these proto-gene sequences enhanced growth, proving their potential for the evolution of new functions.
The new insight could prove important in identifying genes relevant to various medical conditions and biological mysteries. Essential genes that are potential therapeutic targets can be hiding in the heterochromatin, hidden among genomic junk.
Read the whole article: Innovation of heterochromatin functions drives rapid evolution of essential ZAD-ZNF genes in Drosophila.
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