LIGHT-SENSITIVE RESPONSE IN MELANOPHORES OF XENOPUS-LAEVIS .2. RHO ISINVOLVED IN LIGHT-INDUCED MELANIN AGGREGATION

Melanophores of the isolated tail fin of the Xenopus tadpole aggregate melanin granules in response to light. This aggregation was found to be inhibited by subcutaneous injection of exoenzyme C3 of Clostridium botulinum. A 26 kDa protein in homogenate obtained from the Xenopus ta il fin was ADP-ribosylated by exoenzyme C3. This reaction was inhibite d effectively by a monoclonal antibody, anti-Rho mab A5, raised agains t the small GTP-binding protein Rho. The extent of ADP-ribosylation de pended on light and guanine nucleotide. Incubation under illumination partly reduced ADP-ribosylation and the reduction was restored by addi tion of guanine nucleotide during incubation. These findings suggest t hat Rho is involved in the photo-sensitive melanophore response as a s ignal transducer linking photo-stimuli to melanin granule translocatio n with Xenopus melanophores. (C) 1996 Wiley-Liss, Inc.