The Journal of Neuroscience, September 1, 2002, 22(17):7518-7525
Plane of Cell Cleavage and Numb Distribution during Cell Division
Relative to Cell Differentiation in the Developing Retina
Amila O.
Silva,
Cesar E.
Ercole, and
Steven C.
McLoon
Department of Neuroscience, University of Minnesota, Minneapolis,
Minnesota 55455
Progenitor cells in the early developing nervous system can divide
symmetrically, giving rise to two daughter cells that divide again, or
asymmetrically, giving rise to one cell that differentiates and one
that divides again. It has been suggested that the orientation of the
cell cleavage plane during mitosis determines the type of division. A
marker of early cell differentiation, the RA4 antigen, was used to
identify regions of the developing chick retina with and without
differentiating cells, and the orientation of the cleavage plane was
characterized for mitotic figures in each region. No difference was
found in the frequency of any orientation between the regions with or
without differentiating cells. Furthermore, in the region of the retina
with differentiating cells, the RA4 antigen was present in mitotic
figures with every possible orientation. Thus, the orientation of the
cleavage plane appears to be unrelated to whether or not a division
produces a cell that differentiates. It has also been suggested that
the intracellular protein Numb mediates neurogenesis via asymmetric
localization during cell division. Numb localization was compared with
expression of markers of early cell differentiation, the RA4 antigen
and Delta. Differentiating and nondifferentiating cells were found both
with and without Numb expression. Cells with a cleavage plane parallel
to the retinal surface were polarized, such that Numb and/or the RA4
antigen, when present, were only in the daughter cell farthest from the ventricle. These findings indicate a need to reconsider current hypotheses regarding the key features underlying symmetric and asymmetric divisions in the developing nervous system.
Key words:
symmetry of cell division; neuronal differentiation; Notch; Delta; RA4 antigen; neuroepithelial cell; retina; development
Copyright © 2002 Society for Neuroscience 0270-6474/02/22177518-08$05.00/0
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