Neural Competence and Cell Lineage of Gastrula Ectoderm of Newt Embryo

Abstract

The change in the capacity to form neural structures was quantitatively analyzed in both intact and isolated ectoderms of Cynops pyrrhogasrer gastrula. The frequency of explants with induced neural structures abruptly decreases between stage 12c and stage 13b in intact ectoderm, and between 12 hr and 18 hr preculture in isolated ectoderm. The quantitative analysis also made clear that the size of the cell population of induced neural structures was gradually reduced with the aging of the ectoderm. The authors simultaneously examined the cell proliferation of early gastrula ectoderm and confirmed that all ectodermal cells divided at least once within 18 hr at 2 3 T , after which the neural competence of the ectoderm completely disappeared.The relationships between neural competence and cell lineage (cell generation) of the ectoderm are discussed in the light of these findings.It has been generally accepted that the young gastyla ectoderm of an amphibian embryo is pluripotent and there is no difference in the reactivity between the various parts of the ectoderm. The pluripotent reactivity gradually decreases with each corresponding stage of the developmental process, and then the reactivity of each ectodermal part becomes restricted to certain areas which correspond to their future places in the embryo.It is also a well-known fact that the capacity of the ectoderm to form neural structures progressively decreases during the gastrulation process and the neural competence is finally lost at the end of gastrulation (1, 21, 22,25). Furthermore, many investigations (6, 11, 19,26,33) have shown that the neural competence bf the isolated ectoderm gradually disappeared with the aging of the ectoderm in a way similar to that of, in vivo. Some of these studies (1 1, 22) demonstrated that the size of the induced neural structures was reduced with the disappearance of the neural competence of the ectoderm. As for the mechanism for the loss of the competence of the ectoderm, NIEUWKOOP (22) suggested the relationships between the metabolic activity and the loss of the neural competence. KAWAKAMI et al. (15), who tried to analyze primary induction at the cellular level by electrophoretically separating the ectodermal cells, imphasized the possibility that the changes in the competence of presumptive ectoderm must be due to a shift of cell susceptibility to the killing capacity of inducing agents. More recently, GRUNZ (8) reported that the rate of reduction of neural competence was delayed by cycloheximid, a specific inhibitor of protein synthesis. These facts suggest that the loss of neural competence might be a reflection of the metabolic changes of the ectodermal cells themselves.It seems, therefore, most important to analyze neural competence in relation to the cytological and physiological natures of the ectodermal cells. Unfortunately, there have been few studies which have examined the exact cytological and physiological changes in the ectodermal cells during gastrulation. Recently, cytological and physiological changes hav...

Cellular Basis of Neuralization of Induced Neurectoderm in Amphibian Embryogenesis: Changes of Cell Shape, Cell Size, and Cytodifferentiation of the Neurectoderm after Neural Induction

“…Such morphological changes in thickness may reflect intrinsic events during the process of neural induction. This possiblity is supported by the facts that neuralizing determination of the ectoderm is established at or immediately before stage 13b (15) and the ventral ectoderm at this developmental stage has lost neuro-competence (17).…”

Inter and Intratissue Communication During Amphibian Development*

“…Neural competence within the presumptive epidermal ectoderm of the newt embryo decreases abruptly between st. 12c and st. 13b (44). Our data show that all of the P.N.E.…”

“…These changes in properties of the cell surface during gastrulation are related to the adhesion properties of the intercellular membrane as well as the resulting formation and/or breakdown of gap junctions. Both phenomena are involved in the passage of a signal substance into the target cells which occurs during st. 12c and 13b (44).…”

Neural-inducing activity of newly mesodermalized ectoderm

“…The neural competence of presumptive ectoderm gradually decreased during gastrulation and finally disappeared at the late gastrula stage (Chuang 1955;Leikola 1963;Gebhardt and Nieuwkoop 1964;Suzuki and Ikeda 1979). In Cynops gastrulae, Suzuki and Ikeda (1979) reported that presumptive ectoderm cells lost their neural competence at stage 13b gastrula and they found the loss of neural competence to be closely related to the cell lineage of ectoderm.…”

“…In Cynops gastrulae, Suzuki and Ikeda (1979) reported that presumptive ectoderm cells lost their neural competence at stage 13b gastrula and they found the loss of neural competence to be closely related to the cell lineage of ectoderm. They noted that the presumptive ectoderm cells of early gastrula divided at least once during the gastrula stage and lost their neural competence.…”