squidarticle[1] - P roc. Natl. Acad. Sci. USA Vol. 94, pp....

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Proc. Natl. Acad. Sci. USA Vol. 94, pp. 2421–2426, March 1997 Evolution Squid Pax-6 and eye development ( Pax-6 y olfactory organ y evolution mollusc y crystallin) S TANISLAV I. T OMAREV * ² ,P ATRICK C ALLAERTS ,L IDIA K OS § ,R INA Z INOVIEVA ,G EORG H ALDER , W ALTER G EHRING , AND J ORAM P IATIGORSKY * *Laboratory of Molecular and Developmental Biology, National Eye Institute, National Institutes of Health, Bethesda, MD 20892-2730; Department of Cell Biology, Biozentrum, University of Basel, Switzerland, Klingelbergstrasse 70, CH-4056 Basel, Switzerland; and § Laboratory of Genetic Disease Research, National Center for Human Genome Research, Bethesda, MD 20892-2730 Contributed by Walter Gehring, December 23, 1996 ABSTRACT Pax-6 in vertebrates and its homolog eyeless in Drosophila are known to be essential for eye development. Here we investigate the role of Pax-6 in eye development in another major systematic group, molluscs. We demonstrate that alternatively spliced RNAs derived from a single Pax-6 gene in the squid ( Loligo opalescens ) are expressed in the embryonic eye, olfactory organ, brain, and arms. Despite significant sequence differences between squid Pax-6 and Drosophila eyeless in the region outside the paired- and homeodomains, squid Pax-6 is able to induce the formation of ectopic eyes in Drosophila . Our results support the idea that Pax-6 related genes are necessary for eye and olfactory system formation throughout the animal kingdom. Eyes of very diverse type and structure ranging from simple light-sensitive receptors to complex image-forming eyes can be found in the animal kingdom (1–3). Most of the major animal groups comprise species with a simple eye spot. A more elaborate optical system can be found in only six of the animal phyla; these, however, contribute about 96% of the known species (2). Different explanations for the diversity of eyes have been proposed. The morphological differences of the various eyes have been considered as evidence that they did not share a common ancestor and thus are polyphyletic in origin. Indeed, it has been estimated that photoreceptors may have evolved independently 40–60 times (1). An alternative view suggesting a common evolutionary origin of the various eye types has also been proposed (4). Recent data based on the demonstration that the paired domain y homeodomain tran- scription factor, Pax-6 y eyeless, has a critical role in eye devel- opment in vertebrates (5–10) and Drosophila (11) support the idea of a monophyletic origin of the eyes. Heterozygous mutations in Pax-6 of vertebrates are associ- ated with a variety of eye diseases, including aniridia in human and Small eye ( Sey ) in rodents (5, 6, 8). In homozygotes, Pax-6 mutations are lethal due to a complete absence of eyes and nose and severe defects in brain formation (see ref. 12 for a review). The curtailing of normal eyeless expression in the eye primordia of Drosophila leads to a reduction or complete
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This note was uploaded on 10/21/2009 for the course HONORS 250 taught by Professor Staff during the Spring '08 term at University of Michigan.

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squidarticle[1] - P roc. Natl. Acad. Sci. USA Vol. 94, pp....

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