Abstract
The multicellular green alga Volvox carteri forma nagariensis has only two cell types: terminally differentiated somatic cells and reproductive cells. The regA gene maintains the terminally differentiated state of the somatic cells, apparently by repressing transcription of genes required for chloroplast biogenesis and thereby preventing cell growth. Because the RegA protein sequence bore no obvious motifs, we are attempting to identify regions of functional importance by searching for strongly conserved domains in RegA orthologs. Here we report the cloning and characterization of regA from the most closely related known taxon, V. carteri f. kawasakiensis. Given the closeness of the relationship between these two formas, their regA genes are surprisingly different: they differ in the number of introns and by several lengthy indels, and they encode proteins that are only 80% identical. We also serendipitously discovered a paralogous gene immediately upstream of each regA locus. The two regA genes, both upstream paralogs and several genes in Chlamydomonas (the closest unicellular relative of Volvox) encode a conserved region (the VARL domain) that contains what appears to be a DNA-binding SAND domain. This discovery has opened up a new avenue for exploring how regA and the terminally differentiated state that it controls evolved.
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Acknowledgments
We thank Jennifer Brisson, Christina Tuskey, Kristine Bouckaert and Stephanie Buckley for valuable help in various stages of this project and Greg Robertson for helpful comments, and Hisayoshi Nozaki for providing us with a culture of f. kawasakiensis. LD was a Jane Coffin Childs Post-Doctoral Fellow. Support to AH was provided by an NIGMS Initiative for Minority Student Development Grant (R25-GM55036) and Procter and Gamble. This work was supported by grants IBN-9904739 and IBN-0131565 from the National Science Foundation to DLK and grant IBN-0077535 from the National Science Foundation to SMM.
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Communicated by F.-A. Wollman
Nucleotide sequence data reported here are available in the DDBJ/EMBL/GenBank databases under the accession numbers DQ247963 & AF106962
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Duncan, L., Nishii, I., Howard, A. et al. Orthologs and paralogs of regA, a master cell-type regulatory gene in Volvox carteri . Curr Genet 50, 61–72 (2006). https://doi.org/10.1007/s00294-006-0071-4
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DOI: https://doi.org/10.1007/s00294-006-0071-4