Researchers in the field of evolutionary development have long sought to understand how genetic mutations millions of years ago changed embryonic development to yield the diverse animal forms seen today. However, identifying the important mutations is very difficult because they occurred in long-extinct animals, and have been mixed with scores of subsequent mutations. Now, a study from researchers led by New York University develops fruit flies carrying reconstructed ancient genes to reveal how primordial mutations drove major evolutionary changes in embryonic development, the result of which is seen today. The team states they identified two mutations arising over 140 million years ago, now responsible for regulating the development of the head and other structures in virtually all species of present-day flies. The opensource study is published in the journal eLife.
Previous studies show the bicoid (Bcd) gene triggers the formation of structures at the head end of embryos in the fruit fly. Fly embryos lacking the active Bcd protein die early because they form tail structures at both ends. Bicoid shows even the most fundamental aspects of development can change drastically during evolution, a process whose occurrence still remains unclear. The current study inserts ancient DNA into transgenic fly embryos to show most of Bcd’s current functions are attributable to evolutionary changes made over 140 million years ago.
The current study computationally reconstructs ancient gene sequences based on their modern descendants, chemically recreates the genes, and then inserts them into fly embryos, developing transgenic embryos. Results show flies carrying the precursor Bcd gene fail to develop heads, possessing tails at both ends, with none of the key genes involved in head development properly expressed.
The group then introduced every mutation that occurred during the ancient interval of bicoid evolution into the precursor gene. Results show two of the mutations together allowed bicoid to activate a completely new set of target genes. Data findings show when introduced into fly embryos, this mutant version of bicoid activates most of the genes involved in head development in their proper places, and the embryos form recognizable head structures at the anterior end.
The team surmises their study is the first to use ancestral reconstruction in the field of evolutionary biology, enabling them to dissect how molecular changes in an ancient gene fundamentally changed one of the most important processes in animal development. For the future, the researchers state the use of the fruit fly will prove to be an important model organism as many aspects of its genetics and development are shared with humans and other animals.
Source: New York University
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