Neurulation in Mechanically and Chemically Inhibited Amblystoma

Burt, Agnes S.

doi:10.2307/1538273

Cited by 12 publications

(4 citation statements)

References 22 publications

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“…But during the period before neurogenesis, the period that concerns us in the eye, cell death is generally less common. Slow proliferation has been suggested to accompany morphogenesis because mitotic figures were sparse during the shaping of the neural plate and more numerous afterward (Burnside and Jacobson, 1968; Burt, 1943). But these observations were not pursued more rigorously, e.g., by counting cells.…”

Section: Introductionmentioning

confidence: 99%

Modulation of cell proliferation in the embryonic retina of zebrafish (Danio rerio)

Ochocinska

et al. 2000

Dev. Dyn.

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We describe light‐microscopically the development of the embryonic zebrafish eye with particular attention to cell number, cell proliferation, and cell death. The period from 16 to 36 hr post fertilization (hpf) comprises two phases; during the first (16–27 hpf) the optic vesicle becomes the eye cup, and during the second (27–36 hpf) the eye cup begins to differentiate into the neural retina and pigmented epithelium. All cells in the eye primordium are proliferative prior to 28 hpf, and the length of the cell cycle has been estimated to be 10 hr at 24–28 hpf (Nawrocki, 1985). Our cell counts are consistent with that estimate at that age, but not at earlier ages. A 10‐hr cell cycle predicts that the cell number should increase by 7% per hr, but during 16–24 hpf the cell number increased by only 1.5% per hr. Despite the low rate of increase, all cells labeled with bromo‐deoxyuridine, so all were proliferative. We considered three possible explanations for the nearly‐constant cell number in the first phase: proliferation balanced by cell emigration from the eye, proliferation balanced by cell death, and low proliferation caused by a transient prolongation of the cell cycle. We excluded the first two, and found direct support for the third. Previous examinations of the cell cycle length in vertebrate central nervous system have concluded that it increases monotonically, in contrast to the modulation that we have shown. Modulation of the cell cycle length is well‐known in flies, but it is generally effected by a prolonged arrest at one phase, in contrast to the general deceleration that we have shown. © 2000 Wiley‐Liss, Inc.

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Section: Introductionmentioning

confidence: 99%

Modulation of cell proliferation in the embryonic retina of zebrafish (Danio rerio)

Ochocinska

et al. 2000

Dev. Dyn.

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“…The effects of lithium on amphibian development have also been extensively investigated. Treatment of Ambystoma embryos with various concentrations of lithium chloride produced failure of neural tube closure in association with a significant reduction in mitotic activity in the neural plate [17]. In the frog Xenopus Laevis, exposure to lithium during early cleavage stages resulted in ventralised embryos (overdevelopment of the ventral parts of the embryo at the expense of the dorsal parts) whereas treatment during gastrulation induced microcephalia and phase specific deficiencies of the notochord [45,46].…”

Section: Invertebrates and Non-mammalian Vertebratesmentioning

confidence: 99%

“…These early studies were also on the alert for effects on pregnancy outcome, as lithium had been continuously used as an experimental teratogen since the late nineteenth century [15][16][17]. These concerns for the effects of lithium on human reproduction were very real because of the natural history of bipolar mood disorder.…”

Section: Introductionmentioning

confidence: 99%

Teratogenic and Developmental Effects of Lithium

Giles¹,

Bannigan

2006

CPD

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A review is presented on the effects of lithium in therapeutic doses on the outcome of human pregnancy. The results of various studies including cohort, prospective, retrospective and small number case reports indicate that lithium is a "weak" teratogen in humans. The main effects attributable to lithium are, cardiac malformations and babies with increased birth weight. There is a possibility that, in particular, lithium may be associated with the Ebstein anomaly but present evidence cannot definitely affirm or deny this association. Animal studies with lithium using doses comparable to human therapeutic serum levels have not reported any abnormalities. However, higher doses have produced exencephaly, skeletal and craniofacial defects and abnormalities of blood vessel development. Experiments with other vertebrates have shown that lithium affects dorsoventral specification and inhibition of vasculogenesis. Both these effects can be prevented by pretreatment with myo-inositol indicating that lithium interferes with the phosphatidyl inositol cycle. More recent findings have shown that the effects of lithium on invertebrates may be mediated through inhibition of GSK-3beta in the Wnt-GSK-3 pathway.

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“…The explanation they suggest is extremely hypothetical and embodies the principle of attractive forces between surface molecules of cells. Hutchinson (1940Hutchinson ( , 1944 found a slight decrease in number of cells per unit volume of neural plate between stages 1 3 and 16 of Amblystorna, and Burt (1943), using the same species, concluded that neurulation is accompanied by mitosis but that the mitotic rate rises only after closure of the neural folds. Finally, Gillette (1944) observed that during early neurulation neither differential mitotic activity nor increase in cell size occurred.…”

Section: Early Neurogenetic Forces (I) Medullary Plate and Tube Formamentioning

confidence: 99%

Form and Causality in Neurogenesis

Piatt

1948

Biological Reviews

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Summary The causal relationships responsible for the early organization and subsequent structural configuration of the vertebrate central nervous system are poorly understood. This is due in part to the complex nature of the subject but perhaps even more to the fact that causal neurogenesis has not yet attained full status as an independent biological discipline. Those general principles which are known derive largely from the separate fields of experimental embryology and descriptive neurology and are based, for the most part, on a random collection of non‐integrated facts. The source and nature of the data are probably adequate; what is needed is a conscious, co‐ordinated effort to envisage this field of study in its totality and, for immediate purposes, as an end in itself. 1. The early formation of the medullary plate is dependent upon the inductive effect of the mesodermal substratum. Physical contact is probably necessary. Organization of neural ectoderm into medullary plate and tube in the absence of underlying tissue has been reported, but these results are probably due to the disintegrating action of the culture medium upon the inner, uncoated plate cells. The autolysis produced liberates neurogenetic substances responsible for the inductions obtained and the process is considered a pathological one. The morphogenetic forces responsible for the folding of a flat medullary plate into a hollow tube are probably intrinsic to the neural ectoderm itself. An increase in the contractile tension of the superficial gel layer of the external ends of the plate cells may be an important factor. Neither differential water absorption nor localized cellular proliferation seems to play a part in the process. The establishment of polarity and morphological gradients within the neural axis are relatively independent of substrate tissue. Throughout the early stages of neurogenesis the neural ectoderm plays a more active role than has previously been supposed. 2. There exists no valid evidence that neuromeres represent an inherent metamerism of the early neural axis. The segmental arrangement of the spinal ganglia, and probably dorsal and ventral roots as well, is imposed from without by virtue of the proximity of the segmenting axial mesoderm. Mesodermal segmentation is primary; ectodermal segmentation is secondary. The organizing effect of the mesoderm upon the segmentation of the neural tube is more pronounced than certain aspects of the mesodermal‐ectodermal relationship obtaining in earlier stages. 3. The theories of Kappers (neurobiotaxis) and of Bok (stimulogenous fibrillation) are inadequate for solving the complexities of neural differentiation. Neither theory is buttressed by critical experimental evidence and both are highly speculative in nature. Neurobiotaxis and stimulogenous fibrillation still remain the dues ex machina of neurology. 4. Nothing decisive is known concerning the important phenomena of cellular proliferation and differentiation within the central nervous system. Failure to delineate clearly betw...

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Neurulation in Mechanically and Chemically Inhibited Amblystoma

Cited by 12 publications

References 22 publications

Modulation of cell proliferation in the embryonic retina of zebrafish (Danio rerio)

Modulation of cell proliferation in the embryonic retina of zebrafish (Danio rerio)

Teratogenic and Developmental Effects of Lithium

Form and Causality in Neurogenesis

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