Meeting Abstract

45.4  Tuesday, Jan. 5  Convergent evolutionary origin of an eye in the demosponge Amphimedon queenslandica OAKLEY, TH*; RIVERA, AS; OZTURK, N; FAHEY, B; PLACHETZKI, DC; DEGNAN, BM; LEYS, SP; SANCAR, A; Univ. of California, Santa Barbara; Univ. of Richmond; Univ of North Carolina; Univ of Queensland; Univ. of California, Davis; Univ of Queensland; Univ of Alberta; Univ of North Carolina oakley@lifesci.ucsb.edu

All animal eyes examined to date utilize opsin-based phototransduction cascades. We report that the pigment spot eye of a larval sponge (Amphimedon queenslandica) provides an exception to this rule. Although A. queenslandica exhibits behavioral attributes of light perception and a morphological structure meeting the definition of an eye, its genome lacks opsin. Further, conserved transcription factor genes involved in eye development in a diversity of other animals are either absent from the sponge genome or not expressed near the pigment ring eye. We report that the genome of A. queenslandica possesses two cryptochrome/photolyase genes (aqCry1 and aqCry2), members of a light sensitive family of proteins common in eukaryotes. We find with in situ hybridization that one gene, aqCry2 is expressed near or in the pigmented larval eye, and (along with aqCry1) possesses DNA repair activity in an in vitro assay. We report the in vitro action spectrum of the protein aqCry2 and find it lacks characteristics of the behavioral action spectrum of the sponge larvae, reported previously. Taken together, our results indicate that sponge larval eyes represent a case of dramatically convergent evolution with the opsin-based eyes of other animals, but the molecular identity of the photoreceptor remains elusive. If cryptochrome is the photoreceptive gene, it must not act alone. We speculate that the aqCry2 expressed in the larval eye could act as a ‘timekeeper’ since phototaxis is temporary and correlated temporally with aqCry2 expression.