title: Gsg1, Trnp1, and Tmem215 Mark Subpopulations of Bipolar Interneurons in the Mouse Retina.
abstract: How retinal bipolar cell interneurons are specified and assigned to specialized subtypes is only partially understood. In part, this is due to a lack of early pan- and subtype-specific bipolar cell markers. To discover these factors, we identified genes that were upregulated in Blimp1 (Prdm1) mutant retinas, which exhibit precocious bipolar cell development.
  
  
  
  Postnatal day (P)2 retinas from Blimp1 conditional knock-out (CKO) mice and controls were processed for RNA sequencing. Genes that increased at least 45% and were statistically different between conditions were considered candidate bipolar-specific factors. Candidates were further evaluated by RT-PCR, in situ hybridization, and immunohistochemistry. Knock-in Tmem215-LacZ mice were used to better trace retinal expression.
  
  
  
  A comparison between Blimp1 CKO and control RNA-seq datasets revealed approximately 40 significantly upregulated genes. We characterized the expression of three genes that have no known function in the retina, Gsg1 (germ cell associated gene), Trnp1 (TMF-regulated nuclear protein), and Tmem215 (a predicted transmembrane protein). Germ cell associated gene appeared restricted to a small subset of cone bipolars while Trnp1 was seen in all ON type bipolar cells. Using Tmem215-LacZ heterozygous knock-in mice, we observed that β-galactosidase expression started early in bipolar cell development. In adults, Tmem215 was expressed by a subset of ON and OFF cone bipolar cells.
  
  
  
  We have identified Gsg1, Tmem215, and Trnp1 as novel bipolar subtype-specific genes. The spatial and temporal pattern of their expression is consistent with a role in controlling bipolar subtype fate choice, differentiation, or physiology.
authors.affiliation: Department of Ophthalmology, University of Colorado Denver, Aurora, Colorado, United States.
authors.forename: Ko Uoon
authors.initials: KU
authors.lastname: Park
authors.affiliation: Department of Ophthalmology, University of Colorado Denver, Aurora, Colorado, United States.
authors.forename: Grace
authors.initials: G
authors.lastname: Randazzo
authors.affiliation: Department of Pediatrics, Section Hematology/Oncology, University of Colorado Denver, Aurora, Colorado, United States.
authors.forename: Kenneth L
authors.initials: KL
authors.lastname: Jones
authors.affiliation: Department of Ophthalmology, University of Colorado Denver, Aurora, Colorado, United States.
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Brzezinski
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D018797:Cell Cycle Proteins; D002454:Cell Differentiation; D004268:DNA-Binding Proteins; D018507:Gene Expression Regulation, Developmental; D018398:Homeodomain Proteins / Q000096:biosynthesis / Q000235:genetics*; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009687:Nuclear Proteins / Q000096:biosynthesis / Q000235:genetics*; D012313:RNA / Q000235:genetics*; D051245:Retinal Bipolar Cells / Q000166:cytology / Q000378:metabolism*; D017949:Retinal Cone Photoreceptor Cells / Q000166:cytology / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014157:Transcription Factors / Q000096:biosynthesis / Q000235:genetics*
chemical_list: D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D018398:Homeodomain Proteins; D009687:Nuclear Proteins; D014157:Transcription Factors; C581864:Trnp1 protein, mouse; D012313:RNA