title: Loss of citron kinase affects a subset of progenitor cells that alters late but not early neurogenesis in the developing rat retina.
abstract: OBJECTIVE
  To understand how loss of citron kinase (CitK) affects retinal progenitor cells (RPCs) in the developing rat retina.
  
  
  METHODS
  We compared knockout (KO) and wild-type (WT) retinae by immunohistochemistry. The TdT-mediated dUTP terminal nick-end labeling (TUNEL) assay was performed to determine cell death. Pulse-chase experiments using 5-ethynyl-2'-deoxyuridine (EdU) were carried out to interrogate RPC behavior and in turn neurogenesis.
  
  
  RESULTS
  Reverse transcription-polymerase chain reaction analysis showed that CitK was expressed at embryonic day (E)12 and was turned off at approximately postnatal day (P)4. Immunohistochemistry showed CitK being localized as puncta at the apical end of the outer neuroblastic layer (ONBL). Analyses during embryonic development showed that the KO retina was of comparable size to that of WT until E13. However, by E14, there was a reduction in the number of S-phase RPCs with a concomitant increase in TUNEL+ cells in the KO retina. Moreover, early neurogenesis, as reflected by retinal ganglion cell production, was not affected. Postnatal analysis of the retina showed that ONBL in the KO retina was reduced to half the size of that in WT and showed further degeneration. Immunohistochemistry revealed absence of Islet1+ bipolar cells at P2, which was further confirmed by EdU pulse-chase experiments. The CitK KO retinae underwent complete degeneration by P14.
  
  
  CONCLUSIONS
  Our study showed that CitK is not required for a subset of RPCs before E14, but is necessary for RPC survival post E14. This in turn results in normal early embryonic neurogenesis, but severely compromised later embryonic and postnatal neurogenesis.
authors.affiliation: Department of Physiology and Neurobiology, University of Connecticut, Storrs, Connecticut, United States.
authors.forename: Devi Krishna Priya
authors.initials: DK
authors.lastname: Karunakaran
authors.affiliation: Department of Physiology and Neurobiology, University of Connecticut, Storrs, Connecticut, United States.
authors.forename: Nisarg
authors.initials: N
authors.lastname: Chhaya
authors.affiliation: Department of Physiology and Neurobiology, University of Connecticut, Storrs, Connecticut, United States.
authors.forename: Christopher
authors.initials: C
authors.lastname: Lemoine
authors.affiliation: Department of Physiology and Neurobiology, University of Connecticut, Storrs, Connecticut, United States.
authors.forename: Sean
authors.initials: S
authors.lastname: Congdon
authors.affiliation: Department of Physiology and Neurobiology, University of Connecticut, Storrs, Connecticut, United States.
authors.forename: Amye
authors.initials: A
authors.lastname: Black
authors.affiliation: Department of Physiology and Neurobiology, University of Connecticut, Storrs, Connecticut, United States.
authors.forename: Rahul
authors.initials: R
authors.lastname: Kanadia
mesh_terms: D000818:Animals; D002454:Cell Differentiation; D004247:DNA / Q000235:genetics; D005260:Female; D018507:Gene Expression Regulation, Developmental; D007150:Immunohistochemistry; D020287:In Situ Nick-End Labeling; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D055495:Neurogenesis / Q000235:genetics*; D011247:Pregnancy; D011270:Pregnancy, Animal; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D012160:Retina / Q000196:embryology* / Q000378:metabolism; D012165:Retinal Ganglion Cells / Q000166:cytology / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013234:Stem Cells / Q000166:cytology / Q000378:metabolism*
chemical_list: D047908:Intracellular Signaling Peptides and Proteins; D004247:DNA; C115635:citron-kinase; D017346:Protein Serine-Threonine Kinases
keywords: CitK; bipolar cells; progenitor cells; retina