CONICET | Buscador de Institutos y Recursos Humanos

Species that live in the intertidal zone are exposed to the 24-h light-dark cycle and to cyclic ebb andflow of tidal waters. Accordingly, both circadian clocks and biological clocks that oscillate in synchronywith the tide, namely circatidal clocks, have been described in several intertidal organisms. Whetherthese two biological timing systems share common neural and molecular mechanisms remainsunknown.In an effort to identify biological clock components in an intertidal decapod crustacean, the crabCancer productus, we recently cloned homologs of Drosophila genes whose expression is essentialto sustain normal circadian rhythmicity. One of them is the Pigment Dispersing Factor (PDF) gene,expressed by eight pacemaking ventral lateral neurons in each of the flys brain hemispheres. Wehave previously identified two members of the pdf family in C. productus, β-pigment-dispersinghormone I (β-PDH I) and β-PDH II. The distribution of β-pdh I-expressing neurons in the crabs brainis similar to that of PDF in Drosophila. Furthermore, β-PDH I shares closer sequence homology withPDF than PDH II does, and it is expressed in neurons that also show CYCLE-like immunoreactivity inthe crabs brain. Taken together, these results suggest that β-PDH I in C. productus may represent afunctional homolog of PDF, which in Drosophila is a critical peptidergic signal to drive circadianoutputs and to couple the circadian network.To further investigate this possibility we transformed Drosophila pdf-null mutants by overexpressingeither β-PDH I or β-PDH II neuropeptides in the PDF circuit. Both transformants expressed thecorresponding mRNA and peptides in the PDF circuitry. Whereas the circadian locomotor activity of β-pdh I-expressing flies was virtually undistinguishable from pdf-transformed null flies, β-pdh II couldonly accomplish a modest rescue of some of the phenotypes associated with the loss of PDF functionin the pdf01 mutant