EXPRESSION PATTERNS OF THREE PUTATIVE SEXUAL‐SPECIFIC GENES IN THE CENTRIC DIATOM THALASSIOSIRA WEISSFLOGII

An intriguing feature of the diatom life cycle is that sexual reproduction not only generates genetic diversity but also controls cell size. Very little is known, however, about either the frequency or the potential ramifications of sexual events in field populations, due in large part to the difficulties associated with recognizing sexual stages. Our approach has been to identify genes involved in the diatom sexual cycle, with the goal of developing molecular probes to determine when and where sexual reproduction occurs. We are investigating the expression pattern of three genes identified in a sexual reproduction screen. The Sig1, Sig2 and Sig3 genes comprise a gene family, and encode proteins with strong sequence homology to extracellular matrix proteins. We have hypothesized that the Sig proteins are necessary for sperm/egg recognition. Using RT‐PCR, we have shown that transcription of the Sig genes is highly upregulated during the early stages of the sexual cycle, before any morphological changes are apparent. The three genes show significant differences in the exact timing and levels of expression, suggesting different roles for each member of the gene family. We are now employing quantitative RT‐PCR to study their relative transcription levels in more detail. We are also using antibodies made against a recombinant version of the Sig2 protein to look at protein expression levels before and after sexual induction, and to determine where the Sig2 protein localizes in the cell.