title: PTBP-dependent PSD-95 and CamKIIα alternative splicing in the lens.
abstract: OBJECTIVE
  Parallels described between neurons and lens fiber cells include detailed similarities in sub-cellular structures that increasingly show shared expression of genes involved in the construction and function of these structures in neurons. Intriguingly, associated modes of molecular regulation of these genes that had been thought to distinguish neurons have been identified in the lens as well. Both elongated cell types form membrane protrusions with similar size, shape, and spacing that exclude microtubules, contain F-actin, and are coated with the clathrin/AP-2 adaptor. Lenses express glutamate and gamma-aminobutyric acid (GABA) receptors with signaling and channel proteins shown to act together at neuronal membranes. Postsynaptic density protein 95 (PSD-95) and Ca(2+)/calmodulin-dependent protein kinase (CaMKIIα) expression and functions illustrate the integration of aspects of neuronal molecular and cell biology and were investigated here in the lens.
  
  
  METHODS
  Immunofluorescence, immunoblot, and RT-PCR methods were used to assess protein expression and alternative transcript splicing.
  
  
  RESULTS
  We showed the essential dendritic spine scaffold protein PSD-95 is expressed in lenses and demonstrated lens PSD-95 transcripts undergo polypyrimidine tract binding protein (PTBP)-dependent alternative splicing of its pivotal exon 18 required to avoid nonsense-mediated decay, and showed PTBP-dependent alternative splicing of CaMKIIα transcripts in the lens. The PSD-95 protein was observed at fiber cell membranes overlapping with N-methyl-D-aspartate (NMDA) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamate and GABA receptor proteins, tyrosine phosphatase STEP, CaMKIIα, the Ca(V)1.3 calcium channel, and clathrin, which were previously identified at lens fiber cell membranes. During neurogenesis, miR-124 is expressed that suppresses PTBP1 and promotes these splicing events. miR-124 is also expressed in mammalian lenses and upregulated during lens regeneration in amphibians, consistent with previous demonstrations of PTBP1,2 and PTBP-dependent PTBP2 exon 10 splicing in rodent lenses.
  
  
  CONCLUSIONS
  Findings of this dendritic spine scaffold protein and conservation of its key mode of molecular regulation in the lens provides further evidence that key aspects of the neuron morphogenetic program are shared with the lens.
authors.affiliation: Department of Oral Biology, Rutgers SDM, Newark, NJ ; Department of Pharmacology & Physiology, Rutgers BHS.
authors.forename: Peter
authors.initials: P
authors.lastname: Frederikse
authors.affiliation: Department of Oral Biology, Rutgers SDM, Newark, NJ.
authors.forename: Anoop
authors.initials: A
authors.lastname: Nandanoor
authors.affiliation: Department of Oral Biology, Rutgers SDM, Newark, NJ.
authors.forename: Chinnaswamy
authors.initials: C
authors.lastname: Kasinathan
mesh_terms: D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000235:genetics* / Q000378:metabolism*; D018076:DNA, Complementary / Q000235:genetics; D000076122:Disks Large Homolog 4 Protein; D019084:Fluorescent Antibody Technique, Indirect; D015870:Gene Expression; D051528:Guanylate Kinases / Q000235:genetics* / Q000378:metabolism*; D007908:Lens, Crystalline / Q000166:cytology / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D038941:Polypyrimidine Tract-Binding Protein / Q000378:metabolism*; D011817:Rabbits; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014018:Tissue Distribution
chemical_list: D018076:DNA, Complementary; D000076122:Disks Large Homolog 4 Protein; C501447:Dlg4 protein, mouse; D008565:Membrane Proteins; D038941:Polypyrimidine Tract-Binding Protein; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D051528:Guanylate Kinases