Izumi Kawakami

Studies on the heterogeneity of cell populations in amphibian presumptive epidermis, with reference to primary induction

Abstract The cell composition of the presumptive epidermis of Triturus pyrrhogaster gastrula was tested by means of isoelectric electrophoresis. Dissociated cells from the epidermis were electrophoretically divided into three zones; the cell numbers in the three zones in a cathode-to-anode direction, corresponded to 35, 41, and 24%, respectively, of the original cells. Epidermal cells neuralized by acidified Holtfreters solution and cells dissociated from the forebrain of tail-bud embryos yielded electrophoretically a layer of cells at a position corresponding to a cathodal cell layer of the presumptive epidermis. Epidermal cells mesodermalized by bone marrow extract, and cells dissociated from dorsal blastoporal lip, were distributed electrophoretically into two layers at the levels corresponding to the two anodal cell layers of the presumptive epidermis. By means of neuralizing and mesodermalizing treatments, about 38 and 66% of the original dissociated cells of presumptive epidermis were recovered, respectively. Each of these percentages corresponds very closely to that of the cathodal zone and the two anodal zones in the original cell spectrum. These findings suggest the possibility of an originally inhomogeneous developmental potency for each cell species in the presumptive epidermis, and a selective killing effect of neuro-inducing substances on cell species which are destined to form mesodermal tissues and, conversely, a selective destruction by mesoderm-inducing substances of cell species destined to form neural tissue.

Vegetalising factor extracted from the fish swimbladder and tested on presumptive ectoderm ofTriturus embryos

SummaryVegetalising factor was isolated from swimbladder of crusian carp (Carassius auratus) by solubilishing with 8 M urea the precipitate obtained after digesting the swimbladder with collagenase. The urea-soluble fraction vegetalised isolated presumptive ectoderm ofTriturus gastrula and produced both undifferentiated mesodermal and endodermal cells. Brief heating of the fraction changed its capacity to produce organised mesodermal tissues, such as notochord and somite, and the frequency of induction of undifferentiated cells was reduced. By inserting the urea-soluble fraction into the blastocoel of an early gastrula, embryos without epidermis were obtained. Some of the embryos consisted of undifferentiated mesodermal and endodermal cells, but in the remaining ones small fragments of notochord, small numbers of somites and pronephros developed, enclosed by endodermal cells.

STAGING OF NEWT BLASTULA EMBRYOS AND FIRST APPEARANCE OF PRIMARY MESODERMAL COMPETENCE

Using the swimbladder of the crusian carp (Carrasius auratus) as an inductor, the first appearance of mesodermal competence in the presumptive ectoderm of the newt (Triturus pyrrhogaster) blastula was investigated. The time course of embryonic development before the gastrula stage was determined by counting the number of surface cells on a 0.25 mm line at the animal pole. Pregastrula embryos with 2–3, 4–5, 6–7 and 7–8 cells roughly correspond to those at 14, 14–12, 8–6 and 4–0 hr before the beginning of gastrulation. Using presumptive ectoderm of the early gastrula stage, 15 min was found to be the minimum time of contact necessary for the realization of induction. The reactivity of the presumptive ectoderm from pregastrula embryos was tested by 30 min contact. Presumptive ectoderm up to the 4–5 cell stage did not react to the inductor. It may become competent within the next 4–8 hr, since the ectoderm from embryos in the 6–7 cell stage was reactive.

IN VITRO DIFFERENTIATION OF CHICK EMBRYONIC LENS EPITHELIAL CELLS INTO FIBER CELLS

The processes of fiber‐cell formation in the lens epithelium of 9‐day‐old chick embryo in vitro were studied.

DIFFERENCE IN INDUCTIVE EFFECT OF LIVER TISSUES WITH AND WITHOUT PERISINUSOIDAL BASEMENT MEMBRANE

Differential inductive capacities among liver tissues of several animals were examined by anticipating the correlation between the capacity and the completness of perisinusoidal basement membrane.

INDUCTIVE CAPACITIES OF GLOMERULAR BASEMENT MEMBRANES AND DENTINE MATRIX

The inductive capacities of the basement membranes of calf kidney glomeruli and the dentine matrix of the incisors of 23‐day rabbit fetuses were examined on the presumptive ectoderm of Triturus gastrulae. The basement membranes caused almost entirely neural induction and the dentine matrix caused mesodermal induction. These findings suggest that intercellular substances play an important role in the inductive effects of heterologous tissues.

Teratogenic Effects of Chemicals on Early Amphibian Development, with Special Reference to the Lithium Effects*

The specific effects of chemicals on embryonic morphogenesis have proved to be valuable for the analysis of the developmental mechanism in various forms. In 1892-1 897 HERBST discovered remarkable deviations from normal development, which are caused by treating sea-urchin eggs with a dilute LiCl-sea water solution ; viz., the production of exogastrulae. LINDAHL (1936), using the same material, showed that lithium poisons certain reactions characteristic of glycolysis. Abnormal development in amphibian eggs induced by LiCl was reported for the first time by BELLAMY (1919) and LEPLAT (1919). The curious anomalies involve the structures of the head, which show a cyclocephalic serises : acephalia, monorhiny, cyclopia, etc. Moreover, LEHMANN (1937, ’38) obtained Triton embryos lacking part of the notochord, in which the presumptive notochord was converted into somite material, and the somites extended along the median line where they fused. LEHMANN (1937) designated this process as “ mesodermization** ” of the notochord, and he attached great importance to it, regarding it as a characteristic effect of lithium. He further called attention to a phase-specific susceptibility of the archenteron roof to this agent. A similar trend was observed in Triturt/s embryos (I. and I. K. KAWAKAMI, 1951), but in this form the range of sensibility for the production of head malformation is limited to the period from the early gastrula to the early neurula, and the maximum susceptibility exists at the latter stage, as opposed to the middle gastrula stage in LEHMANN’S studies. Concerning the mode of physiological action of lithium in the amphibian embryo, LEHMANN (1937) and RANZI and TAMINI (1939) have suggested, following LINDAHL’S hypothesis on lithium action in the sea-urchin egg, the depression of carbohydrate metabolism. In fact, the glycolysis of lithium-embryos is re-