A Growth Curve of Cell Numbers In the Neural Retina of Embryonic Chicks

Abstract

Growth of cell numbers in a normal embryonic population of neural retinal cells is described. The numbers were estimated from a time shortly after the neural retina first becomes recognizable to a time when numbers of retinal cells have become steady. Cell numbers were estimated in preparations of an entire neural retina dispersed into a suspension of single nuclei which were then counted in a Coulter counter. Growth curve of the In numbers of cells has 3 phases of growth: an exponential phase during which there is steady-state exponential growth, a differentiative phase during which cell proliferation ceases and an end phase when no further change in cell numbers can be detected. The variances of the In numbers of cells were highest during the exponential phase. The variances decreased during the differentiative phase and were at their lowest during the end phase. For variances to decrease requires mechanisms which control the final numbers of cells in the neural retina very precisely. Implications of mechanisms which operate by controlling cell lineages are explored.