Xenopus laevis cement gland as an experimental model for embryonic differentiation. I. In vitro stimulation of differentiation by ammonium chloride.

Ectoblastic cells explanted from the animal pole of young Xenopus laevis gastrulae have been cultured in vitro. When these cells were cultured for five days in standard salt solutions they formed atypical epidermis. When they were first submitted for 6 h to Holtfreter solution containing ammonium chloride and then transferred for five days in standard Barth's solution they underwent differentiation into typical cement gland tissue. The optimum concentration of ammonium chloride was 10 mM. Below and above this concentration the resulting cement glands had a smaller volume. The optimum duration for the initial stimulation with 10 mM ammonium chloride in Holtfreter solution was 6 h. Shorter stimulation times produced only small cement glands. Longer initial incubations in ammonium chloride resulted in progressive dissociation of the explants. To obtain the best differentiation into cement gland it appeared that the pH of the ammonium chloride solution should be between 7-5 and 7-7. When the stimulation is performed under these optimum conditions the cement gland measured after five days of culture accounts for 80-90 percent of the explanted tissue. This means that all or almost all of the competent superficial layer of the ectoblastic cells underwent differentiation into cement gland. No other differentiated tissue was observed in the explants. The cement gland is a very simple organ containing only one single cell type. The gland obtained under the described in vitro conditions is therefore proposed as an experimental model for biochemical studies on early embryonic differentiation.