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    Urochordate βγ-crystallin and the evolutionary origin of the vertebrate eye lens

    Shimeld, S.M. and Purkiss, A.G. and Dirks, R.P.H. and Bateman, O.A. and Slingsby, Christine and Lubsen, N.H. (2005) Urochordate βγ-crystallin and the evolutionary origin of the vertebrate eye lens. Current Biology 15 (18), pp. 1684-1689. ISSN 0960-9822.

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    Abstract

    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 [1]. The vertebrate βγ-crystallin genes encode abundant structural proteins critical for the function of the lens [2]. 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 βγ-crystallin. The crystal structure of Ciona βγ-crystallin is very similar to that of a vertebrate βγ-crystallin domain, except for paired, occupied calcium binding sites. The Ciona βγ-crystallin is only expressed in the palps and in the otolith, the pigmented sister cell of the light-sensing ocellus. The Ciona βγ-crystallin promoter region targeted expression to the visual system, including lens, in transgenic Xenopus tadpoles. We conclude that the vertebrate βγ-crystallins evolved from a single domain protein already expressed in the neuroectoderm of the prevertebrate ancestor. The conservation of the regulatory hierarchy controlling βγ-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.

    Metadata

    Item Type: Article
    School: Birkbeck Schools and Departments > School of Science > Biological Sciences
    Depositing User: Sarah Hall
    Date Deposited: 21 May 2019 10:50
    Last Modified: 21 May 2019 10:50
    URI: http://eprints.bbk.ac.uk/id/eprint/27609

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