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The fragile X mental retardation syndrome in humans is caused by a mutational loss of function of the fragile X mental retardation gene 1 (FMR1). FMR1 is an RNA-binding protein, involved in the development and function of the nervous system. Despite of its medical significance, the evolutionary origin of FMR1 has been unclear. Here, we report the molecular characterization of HyFMR1, an FMR1 orthologue, from the cnidarian hydroid Hydractinia echinata. Cnidarians are the most basal metazoans possessing neurons. HyFMR1 is expressed throughout the life cycle of Hydractinia. Its expression pattern correlates to the position of neurons and their precursor stem cells in the animal. Our data indicate that the origin of the fraxile X related (FXR) protein family dates back at least to the common ancestor of cnidarians and bilaterians. The lack of FXR proteins in other invertebrates may have been due to gene loss in particular lineages.

Chitinases are enzymes that degrade chitin, the second most abundant polymer in nature. They are ubiquitous among living organisms where they play a role in development, food-digestion and innate immunity. We have cloned and characterized the first cnidarian chitinase cDNA from the hydroid Hydractinia. The Hydractinia chitinase exhibits a typical secreted family 18 hydrolases primary structure. In situ hybridization and RT-PCR experiments showed that it is exclusively expressed in ectodermal tissues of the animal, only following metamorphosis while undetectable in embryonic and larval stages. Most prominent expression was observed in the stolonal compartment of colonies, structures that are covered by a chitinous periderm. Chitinase mRNA was detected in new branching points along stolons and in hyperplastic stolons indicating a role of the enzyme in pattern formation and allorecognition. It was also expressed in polyps where it was mostly restricted to their basal portion. This expression pattern suggests that HyChit1 also fulfills a role in host defense, probably against fungal and nematode pathogens. Endodermal expression of HyChit1 has never been observed, suggesting that the enzyme does not participate in food-digestion.