Expression of olfactory receptors during development in Xenopus laevis

A coordinated expression of tissue- and cell-specific genes during developm ent is required to establish the complex functional organization of the ver tebrate olfactory system. Owing to the unique features of its olfactory sys tem and the well-characterized phases of its development, Xenopus laevis wa s chosen as a model organism to study the onset and the temporal and spatia l patterns of expression of olfactory-specific genes. Using RT-PCR and in s itu hybridization, it was found that expression of Xenopus olfactory marker protein and of class I receptors, which are thought to be responsible for the perception of water-soluble odorants, was detectable as early as stage 32, less than 2 days after fertilization. In contrast, expression of class II receptors, which are thought to recognize airborne odours, was not detec ted before stage 49, approximately 12 days after fertilization. The results indicate that the expression of olfactory receptors and marker protein is governed by temporally regulated cues during development.