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Vexin (Vxn) Regulates Neurogenesis and Cell Cycle Exit Downstream of Proneural Factors
Author(s) -
Moore Kathryn,
Logan Mary,
Al Diri Issam,
Steele Michael,
Vetter Monica
Publication year - 2017
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.31.1_supplement.746.1
Subject(s) - biology , xenopus , proneural genes , neurogenesis , microbiology and biotechnology , basic helix loop helix , gene knockdown , cell fate determination , cell cycle , cellular differentiation , neural development , progenitor cell , neural plate , morpholino , transcription factor , gene , genetics , stem cell , dna binding protein
Development of the retina is regulated by sets of proneural basic helix‐loop helix (bHLH) transcription factors that coordinate the generation of multiple cell types in a conserved sequence. These proneural bHLH factors promote the expression of target genes that regulate the timing of differentiation and maintain a balance between proliferation and differentiation. However, how these target genes mediate proneural effects remains incompletely understood. The objective of this study was to identify and characterize novel target genes of proneural bHLH factors. We identified vexin ( vxn ) as a novel target gene for Xenopus laevis proneural bHLH factors. In the developing Xenopus nervous system, Vxn is expressed by progenitors. Vxn encodes a novel protein with a predicted SH3‐family motif and is conserved across vertebrate species. To assess the function of vxn during retinal neurogenesis in Xenopus , we targeted retinal progenitors and performed RNA overexpression or knockdown using antisense vxn morpholinos (MO). We analyzed cell cycle exit, retinal neuron differentiation and changes in gene expression, and assessed subcellular location of Vxn protein. V xn is transiently expressed as retinal progenitors initiate differentiation. Vxn overexpression at neural plate stages inhibited cell proliferation and promoted increased expression of the cyclin‐dependent kinase inhibitor p27Xic1. Both exogenously expressed epitope‐tagged mouse or Xenopus Vxn protein, as well as endogenous Vxn protein, localized to the cell membrane and the nucleus in both the neural plate and retina. We demonstrated that Vxn must localize to the nucleus to promote neural differentiation and cell cycle exit by generating forms of Vxn tagged with either nuclear export or nuclear localization sequences. Overexpression of either Xenopus or mouse vxn in retinal progenitors promoted increased differentiation of early born retinal neurons, and also strongly cooperated with the proneural factor Atoh7 to enhance retinal ganglion cell differentiation. Overexpression of vxn caused reduced retinal progenitor expansion resulting in reduced clone size. Conversely, MO knockdown of vxn inhibited retinal neuron differentiation, preferentially maintaining cells as retinal progenitors and reducing expression of terminal differentiation genes. Thus vxn is expressed in progenitors as they initiate neuronal differentiation, and appears to function in the nucleus to regulate cell cycle exit downstream of proneural bHLH factors during neural development. Support or Funding Information Supported by NEI EY012274 to MLV. Thank you to Constance Dooley, Jianmin Zhang, Kaitllyn Phuong Le and Jacklyn Roberts for technical contributions.