Connexin Gene Mutations

Identification of Connexin 50 (GJA8) Gene Mutations

Authors: Joseph Pecha (primary), Stephanie Mattathil, Sumin Gu, M.D., Jean Jiang, Ph.D.
Date: November 12, 2014

Abstract

Connexins are transmembrane proteins that form gap junctions and hemichannels and allow ions and small molecules to pass from one cell to another or from the cell into its environment, respectively. Since gap junctions are the main means of communication between adjacent cells, they are vital to the function of multicellular organisms. They are formed from membrane proteins called connexins which, when arranged in a hexagonal pattern, form a hemichannel (connexon). Two adjacent hemichannels form a gap junction. Hemichannels allow cells to communicate with other nonadjacent cells (paracrine signaling), with the environment (endocrine signaling), and with their own cells (autocrine signaling). The gap junction network also plays a vital role in normal lens development, transparency, and the maintenance of metabolic homeostasis. Previous studies have shown that when connexin 50 (Cx50) is knocked out, microphthalmia and cataracts occur. We have found that Cx50 is involved in lens cell differentiation. Our preliminary data show that cleavage of this protein occurs under oxidative stress because of protease caspase-3 and newly discovered caspase-1. What do these cleavages by the caspase cascade mean in lens development and the development of eye disorders such as coloboma, microphthalmia, and anophthalmia? Connexin mutations are known to be the cause of many disorders, including skin diseases, deafness, peripheral neuropathy and cataract formation; therefore our hypothesis is that mutations in this gene not only cause cataracts but may also lead to abnormal development of the whole eye, resulting in the three previously mentioned disorders. We received fifty-six DNA samples from patients who had microphthalmia, coloboma, anophthalmia, or cataracts. We attempted to find mutations in the Cx50 (GJA8) gene that would lead us to the conclusion that mutations in this gene cause the patients respective conditions. Single Strand Conformational Polymorphism (SSCP) and Heteroduplex (Hetdx) screening methods were conducted. These methods were applied to twelve primers that altogether covered the entire GJA8 gene, and the DNA bands were visualized through silver staining. Several band shifts observed upon mutation screening indicate that it is probable that mutations in the Cx50 gene cause these diseases. Although these unusual band shifts were discovered, upon sequencing, none were missense mutations, but only polymorphisms. We can conclude that polymorphisms and putative mutations in the Cx50 gene may be involved in the physiological and pathological development of eye. Screening additional patients and studying the correlations between these polymorphisms and abnormal eye development would aid in furthering this work.

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