Expression of the human XPB/ERCC-3 excision repair gene-homolog in the sponge Geodia cydonium after exposure to ultraviolet radiation

The marine demosponge Geodia cydonium encodes a gene, termed GCXPB, which d isplays 62% identity to the human XPB/ERCC-3 gene that specifically correct s the repair defect in xeroderma pigmentosum and in Cockayne's syndrome. Th e cDNA was isolated and characterized the deduced aa sequence, XPB_GEOCY, w ith the calculated size of 91,541 Da comprises the characteristic domains f ound in the related helicases. Phylogenetic tree analysis revealed that the sponge sequence is grouped to the metazoan related XPB/ERCC-3 polypeptides . Northern Blot analyses have been performed with sponge samples collected at different depths, thus exposed to different intensities of UV sunlight i n the field. The intensity of the 2.6 kb band, corresponding to the transcr ipts of the sponge GCXPB gene was highest in those biotopes, which are clos er to the surface of the sea, lower were the expressions in animals from a cave or from depths of 22 to 35 m. Controlled laboratory studies revealed t hat after irradiation of specimens with 300 or 1000 J/m(2) WE light a dose- dependent increase of the steady-state level of GCXPB occurs, values up to 29-fold with respect to the controls which were kept in the dark have been determined. In parallel, the DNA integrity in the sponge samples was measur ed using the sensitive Fast Micromethod(R) assay. The data revealed that th e degree of strand DNA breaks paralleled the increase of expression of the GCXPB gene. From these data it is concluded that the XPB/ERCC-3-like gene i n the sponge G. cydonium is UV light-inducible and hence might be used as b iomarker for UV light exposure in the field. (C) 1998 Elsevier Science B.V. All rights reserved.