Mapping differentiation kinetics in the mouse retina reveals an extensive period of cell cycle protein expression in post-mitotic newborn neurons

Authors

  • Marek Pacal,

    1. Genetics and Development Division, Toronto Western Research Institute, University Health Network, Toronto, Canada
    2. Department of Ophthalmology and Vision Sciences, Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Canada
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  • Rod Bremner

    Corresponding author
    1. Genetics and Development Division, Toronto Western Research Institute, University Health Network, Toronto, Canada
    2. Department of Ophthalmology and Vision Sciences, Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Canada
    3. Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Canada
    • Toronto Western Research Institute, 399 Bathurst Street, Toronto, ON, Canada M5T 2S8
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Abstract

Background: Knowledge of gene expression kinetics around neuronal cell birth is required to dissect mechanisms underlying progenitor fate. Here, we timed cell cycle and neuronal protein silencing/induction during cell birth in the developing murine retina. Results: The pan-cell cycle markers Pcna and Mcm6 were present in the post-mitotic ganglion cell layer. Although confined to the neuroblastic layer (NBL), 6–7% of Ki67+ cells lacked six progenitor/cell cycle markers, and expressed neuronal markers. To define protein extinction/induction timing, we defined G2/M length throughout retinogenesis, which was typically 1–2 h, but <10% cells took double this time. BrdU-chase analyses revealed that at E12.5, Tubb3 (Tuj1) appeared at M-phase, followed by Calb2 and Dcx at ∼2 h, Elavl2/3/4 at ∼4 h, and Map2 at ∼6 h after cell birth, and these times extended with embryonic age. Strikingly, Ki67 was not extinguished until up to a day after cell cycle exit, coinciding with exit from the NBL and induction of late markers such as Map1b/Uchl1/Rbfox3. Conclusions: A minor population of progenitors transits slowly through G2/M and, most importantly, some cell cycle proteins are retained for an unexpectedly long period in post-mitotic neurons. The high-resolution map of cell birth kinetics reported here provides a framework to better define mechanisms that regulate neurogenesis. Developmental Dynamics 241:1525–1544, 2012. © 2012 Wiley Periodicals, Inc.

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