Micro RNAs (miRNAs) are ~ 21- 24 nucleotide long small, non coding RNA molecules that play an important role in gene regulation. miRNAs function post transcriptionally by binding to the 3' untranslated region of their target mRNA. This leads to mRNA degradation or translational inhibition, which reduces the protein yield from the target mRNA. The miRNA processing pathway begins in the nucleus where the conserved proteins Drosha and the dsRNA binding protein DGCR8 are located. miRNA processing continues in the cytoplasm with the RNase III enzyme Dicer.

The impact of miRNAs on development was discovered in Ceanorhabditis elegans. Since then, researchers have investigated its role in signalling pathways, apoptosis, metabolism, cardiogenesis and brain development. Furthermore, it has been proposed that the regulation of gene expression by miRNAs is responsible for differences in morphological complexity, with more complex animals possessing more miRNAs in their genomes than relatively simple animals.

In my diploma thesis I will characterise miRNAs present in the shell forming tissue of the freshwater snail Lymnaea stagnalis, with the aim of identifying miRNAs that are involved in shell formation.

To do this I will isolate miRNAs from the mantle tissue of L. stagnalis using the flashPAGE Fractionator (Ambion). miRNAs will then be concatenated, cloned into a vector and sequenced. These miRNA sequences can then be searched against the draft genome of L. stagnalis (present in the Jackson group), and will shed light on their genomic location and target of regulation. Whole mount in situ hybridisation using probes against precursor-miRNAs should provide insight into the function of these molecules, and whether they are involved in shell formation. Furthermore, I plan to isolate some of the key enzymes involved in miRNA processing, Drosha, DGCR8 and Dicer, and to charaterise their expression patterns during the development of L. stagnalis.