Abstract
Chlamydomonas reinhardtii, Volvox carteri, and their relatives in the family Volvocaceae provide an excellent opportunity for studying how multicellular organisms with differentiated cell types evolved from unicellular ancestors. While C. reinhardtii is unicellular, V. carteri is multicellular with two cell types, one of which resembles C. reinhardtii cytologically but is terminally differentiated. Maintenance of this “somatic cell” fate is controlled by RegA, a putative transcription factor. We recently showed that RegA shares a conserved region with several predicted V. carteri and C. reinhardtii proteins and that this region, the VARL domain, is likely to include a DNA-binding SAND domain. As the next step toward understanding the evolutionary origins of the regA gene, we analyzed the genome sequences of C. reinhardtii and V. carteri to identify additional genes with the potential to encode VARL domain proteins. Here we report that the VARL gene family, which consists of 12 members in C. reinhardtii and 14 in V. carteri, has experienced a complex evolutionary history in which members of the family have been both gained and lost over time, although several pairs of potentially orthologous genes can still be identified. We find that regA is part of a tandem array of four VARL genes in V. carteri but that a similar array is absent in C. reinhardtii. Most importantly, our phylogenetic analysis suggests that a proto-regA gene was present in a common unicellular ancestor of V. carteri and C. reinhardtii and that this gene was lost in the latter lineage.
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Acknowledgments
L.D. thanks William Snell and Steve McKnight for their assistance. We thank Tamra Mendelson and Kevin Omland for the use of their computers, Scott Nichols and Kevin Omland for helpful advice, and Tim Ford for hel** to assemble some of the figures. Support to A. Harryman and A. Howard was provided by an NIGMS Initiative for Minority Student Development Grant (R25-GM55036) and Procter and Gamble. S.B. was supported by National Institutes of Health (NIH) National Research Service (NRSA) Award GM 08663 to the Minority Access to Research Careers (MARC) Undergraduate Student Training in Academic Research (U*STAR) Program at UMBC. This work was supported by Grant IBN-0444896 from the National Science Foundation to S.M.M. The C. reinhardtii and V. carteri genome sequencing work was performed by the Joint Genome Institute (http://www.jgi.doe.gov/) under the auspices of the U.S. Department of Energy’s Office of Science, Biological and Environmental Research Program and the University of California, Lawrence Livermore National Laboratory under Contract No. W-7405-ENG-48, Lawrence Berkeley National Laboratory under Contract No. DE-AC03-76SF00098, and Los Alamos National Laboratory under Contract No. W-7405-ENG-36 and was provided for use in this publication only.
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Duncan, L., Nishii, I., Harryman, A. et al. The VARL Gene Family and the Evolutionary Origins of the Master Cell-Type Regulatory Gene, regA, in Volvox carteri . J Mol Evol 65, 1–11 (2007). https://doi.org/10.1007/s00239-006-0225-5
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DOI: https://doi.org/10.1007/s00239-006-0225-5