title: Calpain-5 Expression in the Retina Localizes to Photoreceptor Synapses.
abstract: We characterize calpain-5 (CAPN5) expression in retinal and neuronal subcellular compartments.
  
  
  
  CAPN5 gene variants were classified using the exome variant server, and RNA-sequencing was used to compare expression of CAPN5 mRNA in the mouse and human retina and in retinoblastoma cells. Expression of CAPN5 protein was ascertained in humans and mice in silico, in mouse retina by immunohistochemistry, and in neuronal cancer cell lines and fractionated central nervous system tissue extracts by Western analysis with eight antibodies targeting different CAPN5 regions.
  
  
  
  Most CAPN5 genetic variation occurs outside its protease core; and searches of cancer and epilepsy/autism genetic databases found no variants similar to hyperactivating retinal disease alleles. The mouse retina expressed one transcript for CAPN5 plus those of nine other calpains, similar to the human retina. In Y79 retinoblastoma cells, the level of CAPN5 transcript was very low. Immunohistochemistry detected CAPN5 expression in the inner and outer nuclear layers and at synapses in the outer plexiform layer. Western analysis of fractionated retinal extracts confirmed CAPN5 synapse localization. Western blots of fractionated brain neuronal extracts revealed distinct subcellular patterns and the potential presence of autoproteolytic CAPN5 domains.
  
  
  
  CAPN5 is moderately expressed in the retina and, despite higher expression in other tissues, hyperactive disease mutants of CAPN5 only manifest as eye disease. At the cellular level, CAPN5 is expressed in several different functional compartments. CAPN5 localization at the photoreceptor synapse and with mitochondria explains the neural circuitry phenotype in human CAPN5 disease alleles.
authors.affiliation: Omics Laboratory, University of Iowa, Iowa City, Iowa, United States 2Department of Ophthalmology & Visual Sciences, University of Iowa, Iowa City, Iowa, United States.
authors.forename: Kellie A
authors.initials: KA
authors.lastname: Schaefer
authors.affiliation: Omics Laboratory, University of Iowa, Iowa City, Iowa, United States 2Department of Ophthalmology & Visual Sciences, University of Iowa, Iowa City, Iowa, United States 3Medical Scientist Training Program, University of Iowa, Iowa City, Iowa, United States.
authors.forename: Marcus A
authors.initials: MA
authors.lastname: Toral
authors.affiliation: Omics Laboratory, University of Iowa, Iowa City, Iowa, United States 2Department of Ophthalmology & Visual Sciences, University of Iowa, Iowa City, Iowa, United States 3Medical Scientist Training Program, University of Iowa, Iowa City, Iowa, United States.
authors.forename: Gabriel
authors.initials: G
authors.lastname: Velez
authors.affiliation: Department of Pediatrics, University of Iowa, Iowa City, Iowa, United States.
authors.forename: Allison J
authors.initials: AJ
authors.lastname: Cox
authors.affiliation: Department of Ophthalmology & Visual Sciences, University of Iowa, Iowa City, Iowa, United States 5Department of Biochemistry, University of Iowa, Iowa City, Iowa, United States.
authors.forename: Sheila A
authors.initials: SA
authors.lastname: Baker
authors.affiliation: Omics Laboratory, University of Iowa, Iowa City, Iowa, United States 3Medical Scientist Training Program, University of Iowa, Iowa City, Iowa, United States.
authors.forename: Nicholas C
authors.initials: NC
authors.lastname: Borcherding
authors.affiliation: Omics Laboratory, University of Iowa, Iowa City, Iowa, United States 2Department of Ophthalmology & Visual Sciences, University of Iowa, Iowa City, Iowa, United States.
authors.forename: Diana F
authors.initials: DF
authors.lastname: Colgan
authors.affiliation: Spinal Cord and Brain Injury Research Center, University of Kentucky, Lexington, Kentucky, United States.
authors.forename: Vimala
authors.initials: V
authors.lastname: Bondada
authors.affiliation: Spinal Cord and Brain Injury Research Center, University of Kentucky, Lexington, Kentucky, United States.
authors.forename: Charles B
authors.initials: CB
authors.lastname: Mashburn
authors.affiliation: Spinal Cord and Brain Injury Research Center, University of Kentucky, Lexington, Kentucky, United States.
authors.forename: Chen-Guang
authors.initials: CG
authors.lastname: Yu
authors.affiliation: Spinal Cord and Brain Injury Research Center, University of Kentucky, Lexington, Kentucky, United States.
authors.forename: James W
authors.initials: JW
authors.lastname: Geddes
authors.affiliation: Barbara & Donald Jonas Stem Cell Laboratory, and Bernard & Shirlee Brown Glaucoma Laboratory, Department of Pathology & Cell Biology, Institute of Human Nutrition, College of Physicians and Surgeons, Columbia University, New York, New York, United States.
authors.forename: Stephen H
authors.initials: SH
authors.lastname: Tsang
authors.affiliation: Department of Pediatrics, University of Iowa, Iowa City, Iowa, United States 9Neurology, University of Iowa, Iowa City, Iowa, United States.
authors.forename: Alexander G
authors.initials: AG
authors.lastname: Bassuk
authors.affiliation: Omics Laboratory, University of Iowa, Iowa City, Iowa, United States 2Department of Ophthalmology & Visual Sciences, University of Iowa, Iowa City, Iowa, United States.
authors.forename: Vinit B
authors.initials: VB
authors.lastname: Mahajan
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002154:Calpain / Q000096:biosynthesis / Q000235:genetics*; D002417:Cattle; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D051379:Mice; D009374:Neoplasms, Experimental; D010786:Photoreceptor Cells / Q000378:metabolism* / Q000473:pathology; D012334:RNA, Neoplasm / Q000235:genetics*; D012160:Retina / Q000378:metabolism / Q000473:pathology; D019572:Retinal Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D012175:Retinoblastoma / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D013569:Synapses / Q000378:metabolism*; D014407:Tumor Cells, Cultured
chemical_list: D012334:RNA, Neoplasm; D002154:Calpain; C494426:Capn5 protein, human