Alicia Howard, Ph.D.


Biological Sciences 2013

Undergraduate Institute: Hampton University

Research Advisor: Stephen Miller, Ph.D.

Current Position: Postdoctoral Fellow, University of Maryland, Baltimore School of Medicine

Description of Research

Volvox carteri forma nagariensis is a close relative of Chlamydomonas reinhardtii that possesses two cell types: large gonidia specialized for reproduction, and small, Chlamydomonas-like somatic cells specialized for motility. The somatic regeneratorgene (regA) encodes a nuclear protein (RegA) that accumulates only in somatic cells and prevents them from reproducing. RegA displays little similarity to other proteins in sequence databases, except that it contains the sorts of homo-polymeric amino acid repeats commonly found in transcription factors. We have identified a domain of RegA that is likely to be functionally important by characterizing orthologs in closely related species. To this end we characterized the ortholog of regA (regA-K) from a closely related taxon, Volvox carteri forma kawasakiensis. The proteins encoded by the two orthologs are surprisingly divergent (only ~80% identical) but are nearly identical in a ~110-aa region (the VARL domain) that contains what appears to be a DNA-binding SAND domain.  I was able to use a full-length version of the regA-K gene to rescue the cell-differentiation phenotype of a nagariensis regA mutant, indicating that the two orthologs are functionally equivalent. Sequencing the region immediately upstream of regA in both genomes led to the discovery of regA paralogs that we have named rlsA-N (innagariensis) and rlsA-K (in kawasakiensis; for regA-like sequence). Both of these genes encode VARL domains that are very similar to that of RegA. Currently my project seeks to characterize rlsA-N and other regA paralogs identified by analysis of the assembled V. carteri f. nagariensis genome, to determine if these genes, like regA, regulate cell fate.