The symbiosis between the mollusc Elysia chlorotica and chloroplasts of its algal prey, Vaucheria litorea, has challenged the understanding of chloroplast biology. E. chlorotica feeds on and retains the algal chloroplasts within its digestive cells. The chloroplasts remain photosynthetically active for months in the animal’s cells devoid of the algal nucleus which encodes approximately 90% of the proteins required for the chloroplasts. To help explain the ability of E. chlorotica to maintain functionally active chloroplasts, horizontal gene transfer (HGT) of V. litorea nuclear genes to the E. chlorotica genome has been hypothesized. However, the extent of HGT, as well as the transcriptional viability of putatively transferred genes, is still largely unknown. To better understand the genetic composition of E. chlorotica, optimization of a fluorescent in situ hybridization (FISH) procedure was performed on both V. litorea and E. chlorotica to develop a direct molecular tool to understand the genetic components involved in this symbiosis. Successful FISH analysis of the chloroplast Rubisco gene (rbcL) was accomplished using whole-mounts of both E. chlorotica and V. litorea. Whole-mount FISH analysis of the E. chlorotica nuclear β-actin gene was accomplished in aposymbiotic E. chlorotica larvae. Sectioned, adult E. chlorotica tissue was successfully hybridized for both the rbcL and β-actin genes. The development of the FISH technique for use on whole-mount sea slugs and intact heterokont algal filaments is the first direct application of FISH and can help elucidate the genetic components required to maintain this remarkable symbiosis.
Davis, Geoffry Austin, "Optimization of a Fluorescent In Situ Hybridization Protocol in the Chloroplast Hosting Mollusc Elysia chlorotica" (2012). Honors College. 37.