Structure and expression of type I keratins in the goldfish optic nerve

The goldfish visual pathway displays continuous growth and development throughout life. In addition, there is a remarkable capacity for functional regeneration in response to injury. The intermediate filament proteins expressed in this pathway are atypical when compared to the static visual pathways of adult higher vertebrates. Glial cells in the goldfish optic nerve express keratins as the major intermediate filament protein, and not glial fibrillary acidic protein.; This study was undertaken to examine the structure and expression of type I keratins in the goldfish optic nerve. These experiments have revealed a complex expression of keratins in this tissue. At least three type I keratins have been identified using both a type I keratin specific antibody and a blot-binding assay using the type II keratin ON{dollar}sb3{dollar} as a probe. Furthermore, the primary structures of two of these type I keratins, and that of a third additional type I keratin, have been elucidated.; One of these type I keratins, designated GK50, is most similar to human keratins 14 and 15, which are normally expressed in complex epithelia and not nervous tissue. The GK50 protein is expressed abundantly in goldfish optic nerve and shows a lower expression in goldfish spinal cord and brain. There was no expression detected in the retina. During optic nerve regeneration in response to nerve crush, the GK50 mRNA shows a localized increase in expression in the injured zone. This contrasts the ON{dollar}sb3{dollar} protein which shows an increase in expression at the crush zone margins.; A second type I keratin, designated as GK48, is structurally similar to human keratin 18. The GK48 protein is the likely type I keratin partner to the type II keratin ON{dollar}sb3{dollar}. The GK48 protein shows a wide distribution of mRNA expression in various goldfish tissues.; The GK49 protein is very similar to the GK50 protein. The expression of this protein is quite limited in the goldfish with mRNA detected in optic nerve, spinal cord and skin.