Mitotic patterns in the optic tectum of the chick during normal development and after early removal of the optic vesicle

Abstract

The number of mitotic figures in the optic tectum of the chick increases from just over 20,000 on the fourth day of incubation (stages 25 and 26) to a peak of approximately 45,000 on the fifth and sixth days (stages 28 and 29). Thereafter, the number declines sharply to about 10,000 and 2,000 on the eighth and ninth days respectively and to as few as 100 and 18 on the eleventh and twelfth days. The dividing cells are not uniformly distributed throughout the tectum but show a clear rostral to caudal gradient such that at every stage the number of mitoses in the caudal half of the tectum exceeds that in its rostral half. In addition the number of mitotic figures in the ventrolateral half of the tectum exceeds that in its dorsomedial half between the fourth and seventh days of incubation, but this pattern is reversed during the last few days of mitotic activity.The process of cell proliferation in the optic tectum appears to be completely independent of the developing eye since there is no significant change in either the total number of mitotic figures in the tectum, or in their spatial distribution, after complete removal of the optic vesicle towards the end of the second day of incubation.Interest in mitotic activity in the developing nervous system has been focused principally upon two problems : the mechanism and timing of cellular division within the neural epithelium, and the role of peripheral factors in regulating cell proliferation in the neural tube and its derivatives. The extensive literature dealing with the first of these problems has recently been reviewed in detail by Watterson ('65) and need not be considered here, although it may be pointed out that there is still no generally accepted explanation for the inward movement of the dividing nuclei towards the luminal surface of the neural epithelium, or for the subsequent separation and outward migration of the daughter cells (see Martin, '67). Rather less attention has been paid to the significance of extrinsic factors in the control of mitotic activity in the nervous system. The findings in a number of studies have been quoted in support of the hypothesis that there is a peripheral regulative effect upon cell proliferation but, as Hamburger ('48) has stressed, much of this evidence is rather indirect and inconclusive. For example, in many experimental studies care has not been taken to distinguish clearly J. EXP. ZOOL., 169: 71-92. between the effects of peripheral changes upon mitotic activity per se, and later effects such as disturbances in neuroblast differentiation and growth, or even degenerative changes in differentiated cells. The evidence which is available from studies based upon actual mitotic counts (rather than total cell counts or volumetric measurements) is somewhat conflicting and at present it is by no means clear to what extent the apparent discrepancies reflect real differences between the central and peripheral nervous systems or between different groups of vertebrates.In one of the earliest quantitative studies of ...

Effects of prevention of afferentation of the development of the chick optic lobe

“…This supports the finding that neurons failing to complete normal circuitry in the chick visual system die during the last week of incubation [11]. However, death of many tectal neuroblasts occurs at 10-11 days incubation [9], a time when all mitotic activity is unaffected by early enucleation [13]. This early neuroblast death appears unrelated to peripheral input from optic fibers or to failure of neuronal connectivity.…”

“…However, the reduced rate of DNA synthesis seen in the non-afferented optic lobe may also play a role. Although major mitotic activity within the optic tectum is over at 11 days of age [13], the DNA content of normal chick optic lobes rises a further 13% between 14 days incubation and hatch (this paper, [17]). …”

Optic tectum morphogenesis: A step‐by‐step model based on the temporal–spatial organization of the cell proliferation. Significance of deterministic and stochastic components subsumed in the spatial organization

“…Appropriately organized in time and space, cell proliferation contributes to morpho-and histogenesis (Cowan et al, 1968;LaVail and Cowan, 1971a;Kahane and Kalcheim, 1998) and patterning (Stuckey et al, 2011). The organized operation of cell behaviors depends on temporal and spatial references settled by signaling centers, i.e., zones of polarizing activity (Freeman and Gurdon, 2002;Green, 2002).…”

“…The IsO installs the reference system for the optic tectum (OT) corticogenesis and the retino-tectal map as early as embryonic day (E) 2 (Martínez, 2001;Hidalgo-Sanchez et al, 2005); however, both processes begin, and proceed along, several days after the IsO appearance indicating that the polarity installed by the IsO persists along the entire OT corticogenesis. It is reasonable assuming that NEcs proliferation is influenced by this polarity because it exhibits a temporal-spatial organization (Cowan et al, 1968;Wilson, 1971;Mazzeo et al, 2004;Rapacioli et al, 2011).…”

“…This study analyzes whether the spatial organization of NEcs proliferation could play a role in the morphogenetic changes the developing OT undergoes during its proliferative phase, i.e., between E2 and E10 (Cowan et al, 1968). This study also presents a biomathematical approach that could provide a conceptual framework to analyze a recurrent and controversial point in developmental biology: the problem about ''determinism'' and ''stochasticity'' and their possible role in developing organisms (Bronk et al, 1968;Saunders et al, 2002;Meng et al, 2004;Song et al, 2006;Raj et al, 2010;Zernicka-Goetz and Huang, 2010;Wu et al, 2011).…”