IKNM

An epithelium is a sheet of polarized cells that extend from an apical surface to a basal lamina. Mitotic events in a proliferating epithelium are restricted to the apical pole, where the centrosomes are located. A hallmark of the vertebrate neuroepithelium is interkinetic nuclear migration (IKNM), originally described by Sauer (1935). Sauer suggested a model in which mitosis at the apical surface is followed by a smooth basal descent of the nucleus during G1, and, after S phase, a gradual ascent back to the apical surface for the next mitosis, like an elevator descending to the bottom floor, pausing, and then smoothly rising again (Miyata, 2008).
The dramatic elongation of progenitor cells and the variation in the apicobasal position of their nuclei gives the vertebrate neuroepithelium a pseudostratified (multilayered) appearance. It is suggested that this cellular morphology has arisen to maximize the density of generative cells per unit area of apical surface (Fish et al., 2008). In line with this idea, one function of IKNM may simply be to the move nuclei of postmitototic progenitors away from the apical surface, making room for other mitotic cells.
Norden et al. 2009. Cell. 138:1195-208.

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