Characterization of a transient TCF/LEF-responsive progenitor population in the embryonic mouse retina.
OBJECTIVE
High mobility group (HMG) transcription factors of the T-cell-specific transcription factor/lymphoid enhancer binding factor (TCF/LEF) family are a class of intrinsic regulators that are dynamically expressed in the embryonic mouse retina. Activation of TCF/LEFs is a hallmark of the Wnt/beta-catenin pathway; however, the requirement for Wnt/beta-catenin and noncanonical Wnt signaling during mammalian retinal development remains unclear. The goal of the study was to characterize more fully a TCF/LEF-responsive retinal progenitor population in the mouse embryo and to correlate this with Wnt/beta-catenin signaling.


METHODS
TCF/LEF activation was analyzed in the TOPgal (TCF optimal promoter) reporter mouse at embryonic ages and compared to Axin2 mRNA expression, an endogenous readout of Wnt/beta-catenin signaling. Reporter expression was also examined in embryos with a retina-specific deletion of the beta-catenin gene (Ctnnb1), using Six3-Cre transgenic mice. Finally, the extent to which TOPgal cells coexpress cell cycle proteins, basic helix-loop-helix (bHLH) transcription factors, and other retinal cell markers was tested by double immunohistochemistry.


RESULTS
TOPgal reporter activation occurred transiently in a subpopulation of embryonic retinal progenitor cells. Axin2 was not expressed in the central retina, and TOPgal reporter expression persisted in the absence of beta-catenin. Although a proportion of TOPgal-labeled cells were proliferative, most coexpressed the cyclin-dependent kinase inhibitor p27/Kip1.


CONCLUSIONS
TOPgal cells give rise to the four earliest cell types: ganglion, amacrine, horizontal, and photoreceptor. TCF/LEF activation in the central retina does not correlate with Wnt/beta-catenin signaling, pointing to an alternate role for this transcription factor family during retinal development.
Fuhrmann
Sabine
S
Department of Ophthalmology and Visual Sciences, Moran Eye Center, University of Utah, Salt Lake City, Utah 84132, USA. sabine.fuhrmann@hsc.utah.edu
Riesenberg
Amy N
AN
Mathiesen
Amber M
AM
Brown
Erinn C
EC
Vetter
Monica L
ML
Brown
Nadean L
NL
D000818:Animals; D060466:Axin Protein; D051792:Basic Helix-Loop-Helix Proteins / Q000378:metabolism; D002452:Cell Count; D018797:Cell Cycle Proteins / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000235:genetics; D053595:Embryonic Stem Cells / Q000378:metabolism*; D019084:Fluorescent Antibody Technique, Indirect; D017403:In Situ Hybridization; D051379:Mice; D008822:Mice, Transgenic; D012333:RNA, Messenger / Q000378:metabolism; D012160:Retina / Q000196:embryology*; D051820:TCF Transcription Factors / Q000378:metabolism*; D051153:Wnt Proteins / Q000378:metabolism; D051176:beta Catenin / Q000378:metabolism
D060466:Axin Protein; D051792:Basic Helix-Loop-Helix Proteins; D018797:Cell Cycle Proteins; D003598:Cytoskeletal Proteins; D012333:RNA, Messenger; D051820:TCF Transcription Factors; D051153:Wnt Proteins; D051176:beta Catenin; C111729:Axin2 protein, mouse