Ancient biological functions of present day DNA-damaging enzymes involved in the immune system

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The goal of this research program is to understand forms and functions of DNA damaging processes in fish. The human immune system uses DNA damage in the form of mutations as well as double strand DNA breaks (DSBs) to initiate the diversification of antigen receptor genes in lymphocytes. Our central hypothesis is that orthologous version of these DNA damaging enzymes in fish are involved in biological roles beyond the immune system, possibly in epigenetic genome reprogramming and development.**** All biological organisms have multiple DNA damage sensing, checkpoint and repair pathways. Consequently cells devote much energy to faithful maintenance and repair of their DNA sequence. In this light, the immune system of jawed vertebrates represents an exception. It is the sole example in all of biology where cells, in the course of their normal development and function, actively mutate and physically reorganize their own genomic DNA in a site-specific manner. The usage of DNA damage by immune systems is thought to have first appeared in cartilaginous fish. **** We have recently discovered that orthologous version of some DNA damaging enzyme involved in the human immune system have distinct activity profiles in specific fish species, and thereby mediate functions that are entirely outside the immune system. Based on this finding, we are proposing a new research program to broadly examine DNA damaging enzymes and their biological functions in the jawless vertebrate sea lamprey, sharks which are cartilaginous fish, and several species of bony fish including Atlantic cod, salmon and coelacanth. Our objectives are to 1) clone and characterize DNA damaging enzymes in these species, 2) examine tissue-specific expression patterns of these enzymes in response to immune stimuli and during development, 3) express, purify and examine the biochemical differences amongst fish DNA damaging enzymes, and 4) compare the biological functions of fish DNA damaging enzymes using genetically modified cells and transgenic animal models.**** If our hypothesis is correct, we expect to find that DNA damaging enzymes in some or all of these fish species have distinct tissue expression patterns and/or different biochemical properties as compared to their mammalian counterparts or each other. Our hypothesis also predicts that these enzymes can prompt different DNA damage responses and carry out divergent biological functions when expressed in cell lines or in transgenic animals. ****This research program represents a new direction for my laboratory and we have initiated local, national and international collaborations with experts in fish biology and immunology. Regardless of whether results support our hypothesis, we will gain a comprehensive understanding of the forms and functions of fish DNA damaging enzymes. Thus, the proposed research will advance knowledge in the fields of fish biology, immune system evolution and DNA damage/repair.**