Shimeld, Sebastian M. and Purkiss, Andrew G. and Dirks, R.P.H. and Bateman, Orval A. and Slingsby, Christine and Lubsen, N.H. (2005) Urochordate beta gamma-crystallin and the evolutionary origin of the vertebrate eye lens. Current Biology 15 (18), pp. 1684-1689. ISSN 0960-9822.
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A refracting lens is a key component of our image-forming camera eye; however, its evolutionary origin is unknown because precursor structures appear absent in nonvertebrates . The vertebrate beta gamma-crystallin genes encode abundant structural proteins critical for the function of the lens . We show that the urochordate Ciona intestinalis, which split from the vertebrate lineage before the evolution of the lens, has a single gene coding for a single domain monomeric beta gamma-crystallin. The crystal structure of Ciona beta gamma-crystallin is very similar to that of a vertebrate beta gamma-crystallin domain, except for paired, occupied calcium binding sites. The Ciona beta gamma-crystallin is only expressed in the palps and in the otolith, the pigmented sister cell of the light-sensing ocellus. The Ciona beta gamma-crystallin promoter region targeted expression to the visual system, including lens, in transgenic Xenopus tadpoles. We conclude that the vertebrate beta gamma-crystallins evolved from a single domain protein already expressed in the neuroectoderm of the prevertebrate ancestor. The conservation of the regulatory hierarchy controlling beta gamma-crystallin expression between organisms with and without a lens shows that the evolutionary origin of the lens was based on co-option of pre-existing regulatory circuits controlling the expression of a key structural gene in a primitive light-sensing system.
|Keyword(s) / Subject(s):||sponge geodia-cydonium, ciona-intestinalis, brain, proteins, photoreceptors, superfamily, chordate|
|School or Research Centre:||Birkbeck Schools and Research Centres > School of Science > Biological Sciences|
|Depositing User:||Sandra Plummer|
|Date Deposited:||24 Jan 2006|
|Last Modified:||17 Apr 2013 12:32|
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