Expression Pattern of Paralemmins in Developing Lens and Retina Suggests Multiple Functions in the Eye

Abstract

Abstract: : Purpose: Three related genes, paralemmin (Palm), paralemmin 2 (Palm2) and palmdelphin (PalmD) have been identified in both the mouse and human genomes. Previous studies have reported high levels of Palm expression in the brain and in various other tissues including the adult lens. It has been proposed that Palm, by its association with the plasma membrane, plays a specific role in controlling the shape of lens fiber cells. Microarray analysis of RNA obtained from Pax6 heterozygous lenses raised the possibility that Palm expression is regulated by the transcription factor Pax6. Methods:Immunohistochemistry using an anti–Palm antibody was performed in E9.5–E16.5 mouse embryos as well as in 7 day and 25 week postnatal eyes. Quantitative RT–PCR analysis of Palm, Palm2 and PalmD was performed using total RNAs extracted from the cerebellum, forebrain, lens, retina and cornea of newborn and postnatal mice. Expression levels were normalized using ß2–microglobulin. Results:Our analysis revealed initial expression of Palm in the surface ectoderm and lens placode at E9.5 and the optic vesicle at E10.5. As development progresses, Palm is present at the membranes of both lens epithelial and fiber cells and continues to be expressed throughout the adult lens. As the optic vesicle develops into the retina, high levels of Palm protein are detected transiently in the processes projecting from the developing ganglion cells to the optic nerve. Later, transient upregulation of Palm is also seen postnatally in the developing inner plexiform layer. This trend is also seen in cultured chick retinal cells with higher levels of Palm protein detectable in early compared to late cultures. An analysis of the relative expression levels of Palm, Palm2, and PalmD revealed the highest level of expression in the newborn forebrain with Palm2 expression surpassing Palm and PalmD. In the lens, expression of Palm2 was also the greatest with this trend continuing postnatally. Conclusions:The three genes comprising the paralemmin family are expressed in the lens and retina as well as in the forebrain and cerebellum. Since Palm can drive the elongation of cellular processes, Palm and Palm2 may both control the shape of lens fiber cells.

Keywords: gene/expression • retina