Abstract
BackgroundParalemmin (Palm) is a prenyl-palmitoyl anchored membrane protein that can drive membrane and process formation in neurons. Earlier studies have shown brain preferred Palm expression, although this protein is a major water insoluble protein in chicken lens fiber cells and the Palm gene may be regulated by Pax6.MethodsThe expression profile of Palm protein in the embryonic, newborn and adult mouse eye as well as dissociated retinal neurons was determined by confocal immunofluorescence. The relative mRNA levels of Palm, Palmdelphin (PalmD) and paralemmin2 (Palm2) in the lens and retina were determined by real time rt-PCR.ResultsIn the lens, Palm is already expressed at 9.5 dpc in the lens placode, and this expression is maintained in the lens vesicle throughout the formation of the adult lens. Palm is largely absent from the optic vesicle but is detectable at 10.5 dpc in the optic cup. In the developing retina, Palm expression transiently upregulates during the formation of optic nerve as well as in the formation of both the inner and outer plexiform layers. In short term dissociated chick retinal cultures, Palm protein is easily detectable, but the levels appear to reduce sharply as the cultures age. Palm mRNA was found at much higher levels relative to Palm2 or PalmD in both the retina and lens.ConclusionPalm is the major paralemmin family member expressed in the retina and lens and its expression in the retina transiently upregulates during active neurite outgrowth. The expression pattern of Palm in the eye is consistent with it being a Pax6 responsive gene. Since Palm is known to be able to drive membrane formation in brain neurons, it is possible that this molecule is crucial for the increase in membrane formation during lens fiber cell differentiation.
Highlights
Paralemmin (Palm) is a prenyl-palmitoyl anchored membrane protein that can drive membrane and process formation in neurons
Overexpression of the canonical form of Pax6 in lens fiber cells (Pax6 con transgenics) results in cataracts typified by incomplete lens fiber cell elongation and denucleation, instability of the transcription factor c-Maf and a drastic downregulation of βB1-crystallin expression [21] while overexpression of the Pax6 (5a) splice form results in cataracts without the changes in cMaf stability [22]
Microarray analysis was previously performed on lenses from both Pax6 transgenics and mice heterozygous for a Pax6 null allele and 13 genes were found to be upregulated in the transgenics and downregulated in the heterozygous knockout mice [23]
Summary
Paralemmin (Palm) is a prenyl-palmitoyl anchored membrane protein that can drive membrane and process formation in neurons. A number of studies have identified the expression of proteins with known roles in neuronal function in the lens [7,8,9,10,11,12] and proteins important in lens function in the retina [13,14]. This may partially be due to the need of both retinal neurons and lens fiber cells to develop elaborated plasma membranes for their function [15,16,17]. Microarray analysis was previously performed on lenses from both Pax (con) transgenics and mice heterozygous for a Pax null allele and 13 genes were found to be upregulated in the transgenics and downregulated in the heterozygous knockout mice [23]
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