Expression of Class III ß–Tubulin Isotype in Developing Retina

Abstract

Abstract: : Purpose: Most α– and ß–tubulin isotypes are universal constituents of microtubules; however, class III ß–tubulin is neurone–specific. It is not clear whether preferred expression of class III ß–tubulin in neurones is due to its structural suitability with the neuronal environment, and/or neuronal morphology (such as long axon bearing retinal ganglion cells), or due to involvement of genes of certain isotypes in specific developmental programs. Retina comprises neurones of varied morphology, and the sequence of neurogenesis is well known; therefore expression of class III ß–tubulin in this tissue could shed light on this question. Thus, we investigated the developmental expression of this protein in retina to identify the cell types expressing it. Methods: Immunohistochemistry was done using an antibody against class III ß–tubulin and other retinal cell specific markers (calbindin for horizontal cells, peanut agglutinin for cone photoreceptors) in adult retina of mice. Rabbit and human retinas were used to investigate if there are any species–specific differences. Results: Class III ß–tubulin was found in ganglion cells, certain amacrine cells and cone photoreceptors. Class III ß–tubulin was already expressed in the earliest developmental stage studied (embryonic day 14) in the developing nerve fiber layer, and became distinct at postnatal day 0 in cells located in the ganglion cell layer (ganglion and displaced amacrine cells), proximal parts of the neuroblastic/inner nuclear layer (amacrine cells) and distal part of neuroblastic/outer nuclear layer (photoreceptors). In one animal, Class III–tubulin containing bodies were found in the retinal pigment epithelium cells. No significant differences were observed across species. Conclusions: Results show that the expression of class III ß–tubulin was not related to cell morphology or cell function, but rather to the cell lineage (early born retinal neurones) suggesting that the expression of class III ß–tubulin in certain cell types may be due to the cell specific developmental program. The predominant expression of class III ß–tubulin in retinal ganglion cells and the reported influence of class III ß–tubulin expression on microtubule dynamics raise the interesting possibility of its involvement in pathogenesis of glaucoma.

Keywords: ganglion cells • cytoskeleton • retinal development