Genetic chimeras reveal the autonomy requirements for Vsx2 in embryonic retinal progenitor cells.
BACKGROUND
Vertebrate retinal development is a complex process, requiring the specification and maintenance of retinal identity, proliferative expansion of retinal progenitor cells (RPCs), and their differentiation into retinal neurons and glia. The homeobox gene Vsx2 is expressed in RPCs and required for the proper execution of this retinal program. However, our understanding of the mechanisms by which Vsx2 does this is still rudimentary. To define the autonomy requirements for Vsx2 in the regulation of RPC properties, we generated chimeric mouse embryos comprised of wild-type and Vsx2-deficient cells.


RESULTS
We show that Vsx2 maintains retinal identity in part through the cell-autonomous repression of the retinal pigment epithelium determinant Mitf, and that Lhx2 is required cell autonomously for the ectopic Mitf expression in Vsx2-deficient cells. We also found significant cell-nonautonomous contributions to Vsx2-mediated regulation of RPC proliferation, pointing to an important role for Vsx2 in establishing a growth-promoting extracellular environment. Additionally, we report a cell-autonomous requirement for Vsx2 in controlling when neurogenesis is initiated, indicating that Vsx2 is an important mediator of neurogenic competence. Finally, the distribution of wild-type cells shifted away from RPCs and toward retinal ganglion cell precursors in patches of high Vsx2-deficient cell density to potentially compensate for the lack of fated precursors in these areas.


CONCLUSIONS
Through the generation and analysis of genetic chimeras, we demonstrate that Vsx2 utilizes both cell-autonomous and cell-nonautonomous mechanisms to regulate progenitor properties in the embryonic retina. Importantly, Vsx2's role in regulating Mitf is in part separable from its role in promoting proliferation, and proliferation is excluded as the intrinsic timer that determines when neurogenesis is initiated. These findings highlight the complexity of Vsx2 function during retinal development and provide a framework for identifying the molecular mechanisms mediating these functions.
Department of Ophthalmology and Visual Sciences, John A Moran Eye Center, University of Utah, 65 Mario Capecchi Drive, Salt Lake City, UT, 84132, USA. crystal.cornett@utah.edu.|Interdepartmental Program in Neuroscience, University of Utah, 20 North 1900 East, Salt Lake City, UT, 84132, USA. crystal.cornett@utah.edu.
Crystal L
CL
Sigulinsky
Department of Ophthalmology and Visual Sciences, John A Moran Eye Center, University of Utah, 65 Mario Capecchi Drive, Salt Lake City, UT, 84132, USA. massiell.german@hsc.utah.edu.
Massiell L
ML
German
Department of Ophthalmology and Visual Sciences, John A Moran Eye Center, University of Utah, 65 Mario Capecchi Drive, Salt Lake City, UT, 84132, USA. amanda.leung@utah.edu.|Department of Neurobiology and Anatomy, University of Utah, 20 North 1900 East, Salt Lake City, UT, 84132, USA. amanda.leung@utah.edu.
Amanda M
AM
Leung
Department of Ophthalmology and Visual Sciences, John A Moran Eye Center, University of Utah, 65 Mario Capecchi Drive, Salt Lake City, UT, 84132, USA. anna.clark@hsc.utah.edu.
Anna M
AM
Clark
Department of Ophthalmology and Visual Sciences, John A Moran Eye Center, University of Utah, 65 Mario Capecchi Drive, Salt Lake City, UT, 84132, USA. sanghee.yun@utsouthwestern.edu.|Department of Neurobiology and Anatomy, University of Utah, 20 North 1900 East, Salt Lake City, UT, 84132, USA. sanghee.yun@utsouthwestern.edu.
Sanghee
S
Yun
Department of Ophthalmology and Visual Sciences, John A Moran Eye Center, University of Utah, 65 Mario Capecchi Drive, Salt Lake City, UT, 84132, USA. ed.levine@utah.edu.|Department of Neurobiology and Anatomy, University of Utah, 20 North 1900 East, Salt Lake City, UT, 84132, USA. ed.levine@utah.edu.
Edward M
EM
Levine
D000818:Animals; D002455:Cell Division; D002678:Chimera; D004624:Embryo Transfer; D005260:Female; D017930:Genes, Reporter; D018398:Homeodomain Proteins / Q000235:genetics / Q000502:physiology*; D060850:LIM-Homeodomain Proteins / Q000502:physiology; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D051739:Microphthalmia-Associated Transcription Factor / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D009030:Mosaicism; D058953:Neural Stem Cells / Q000378:metabolism*; D055495:Neurogenesis / Q000235:genetics*; D009457:Neuroglia / Q000166:cytology; D009928:Organ Specificity; D012160:Retina / Q000166:cytology / Q000196:embryology*; D012165:Retinal Ganglion Cells / Q000166:cytology; D014157:Transcription Factors / Q000172:deficiency / Q000235:genetics / Q000502:physiology*
D018398:Homeodomain Proteins; D060850:LIM-Homeodomain Proteins; C489784:Lhx2 protein, mouse; D051739:Microphthalmia-Associated Transcription Factor; C497235:Mitf protein, mouse; D014157:Transcription Factors; C088975:Vsx2 protein, mouse