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Y. Takada, R. N. Fariss, P. A. Sieving, R. A. Bush; Differential Expression of Protocadherin 15 Isoforms in Mouse Retina by Light and Electron Microscopy. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4483.
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© ARVO (1962-2015); The Authors (2016-present)
Protocadherin15 (Pcdh15) belongs to the cadherin family of adhesion molecules. Mutations in human PCDH15 are responsible for Usher syndrome type 1 (USH1F), characterized by congenital profound deafness, vestibular areflexia and severe early-age retinitis pigmentosa (RP). In the mouse, mutations of Pcdh15 cause the Ames waltzer phenotype, including deafness and circling behavior. Reduced ERG responses in the absence of photoreceptor degeneration has also been reported. The function of Pcdh15 in the retina is currently unclear. There are four classes of isoforms of Pcdh15 based on the cytoplasmic domain, each with numerous alterative RNA splice variants. We analyzed the expression and the localization of Pcdh15 isoforms in the mouse retina to explore the possibility that overlapping expression patterns could result in compensation for mutations in one class of isoforms by another and modulate the severity of the retinal phenotype.
Specific validated antibodies against each of three alternative cytoplasmic domains of protocadherin 15, referred to as Pcdh15-CD1, -CD2 and -CD3, and against the extracellular ectodomain, were used to perform immunoblotting on protein extracts and light and electron microscopic immunohistochemistry on sections from normal mouse retina at P1 to P42.
CD1 and CD3 antibodies detected different molecular sizes of Pcdh15 on immunoblots. The extracellular domain antibody labeled the same band as anti-CD1, and anti-CD2 did not detect any protein on immunoblots or sections. Immunohistochemistry with CD1 and CD3 antibodies showed differential localization of Pcdh15 isoforms in the inner retina during postnatal retinal development into adulthood. Only CD1 and ectodomain antibodies labeled photoreceptors. ImmunoEM microscopy revealed that CD1 and ectodomain were present on photoreceptor calycal processes.
The CD1 and CD3 isoforms are expressed in retina but have distinctive staining patterns throughout development, which suggests they also have independent functions. We did not see a pattern of staining to suggest that CD3 isoforms could compensate for the loss of CD1 isoform function in photoreceptors and modulate the severity of photoreceptor degeneration in Pcdh15 mutant mice. Pcdh15 CD1 isoforms may play a novel role in the structure and function of photoreceptor calycal processes.
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