INTER AND INTRATISSUE COMMUNICATION DURING AMPHIBIAN DEVELOPMENT*

Close juxtaposition between inducing chordamesoderm and reacting neuroectoderm is a prerequisite for neural induction in Xenopus laevis

The results of this study indicate that the induction of the central nervous system in Xenopus laevis depends on the close juxtaposition of inducing chordamesoderm and reacting ectoderm, which is necessary for the short distance migration of neural inducing factors. The examination of the neuroectoderm-chordamesoderm interface at intervals of 1 h up to 5 h showed that the onset of neural induction is correlated to the degree of contact formation between ectodermal and mesodermal cells. In the ectoderm cells the number of coated pits, a feature of receptor-mediated endocytosis, is increased. Furthermore there exist telophase bridges between some ectoderm cells, which are possibly correlated to secondary cell interactions.

Multicellular spheroids. A review on cellular aggregates in cancer research

Cellular aggregates have been used in developmental biology and in experimental cancer research for several decades. Spherical aggregates of malignant cells, i.e. multicellular tumor spheroids, may serve as in vitro models of tumor microregions and of an early, avascular stage of tumor growth. The similarities between the original tumor and the respective spheroids include volume growth kinetics, cellular heterogeneity, e.g. the induction of proliferation gradients and quiescence, as well as differentiation characteristics, such as the development of specific histological structures or the expression of antigens. Research using cell aggregates has been focussed on mechanisms involved in the control of proliferation, invasion and metastasis. Immunological studies with spheroids have resulted in the characterization of defense cells which are responsible for specific host-versus-tumor reactions. The vast majority of investigations on spheroids concerns the simulation of therapy with regard to various treatment modalities, combination treatments and systematic analyses of using various endpoints in predictive assays. Only a few pathophysiological studies on the interrelationship among tumor-specific micromilieu, cellular metabolism, proliferative status, and cellular viability have been undertaken with the spheroid model up to now. Since these studies are indicative of a large influence of the cellular microenvironment on basic biological properties of cancer cells, investigations of these epigenetic mechanisms should be intensified in future research on cell aggregates. Similarly, the molecular basis of the biological peculiarities found in malignant cells grown as three-dimensional aggregates has to be investigated more intensively.

Cell-to-cell contact in primary embryonic induction: effects of lectin on electrical coupling and neural induction

The effects of lectin (concanavalin A; ConA) on the electrical coupling between inducing chorda-mesoderm and reacting ectoderm cells, and the realization of neural induction were investigated. The electrical coupling between cells of the chorda-mesoderm of the late gastrula (stage 13b) and the competent ectoderm or Con-A-treated ectoderm of the early gastrula (stage 12a) was measured. Neural induction was tested with ectoderm explants which had been combined with the inducing chorda-mesoderm for 1, 3 and 6 h. Electrical coupling was observed after 3 h. By 6 h, the coupling ratio had recovered to the same level as that between the homogeneous germ-layer cells. However, the electrical coupling did not recover in the combinant with Con-A-treated ectoderm. This suggests that Con-A disturbs close cell contact between the ectoderm and chorda-mesoderm cells. Neural induction was realized in the ectoderm which was combined with chorda-mesoderm for more than 3 h; this occurred parallel to the recovery of electrical coupling. In contrast, Con-A treatment (50 micrograms/ml) of the competent ectoderm for 30 min prevented neural induction. After 3 h of contact, the neural induction of Con-A-treated ectoderm was only one-third of that of the control ectoderm. The present study suggests that cellular contact between the inducing mesoderm and the ectoderm target cells plays an important role in the realization of neural induction.

Closing and opening of gap junction pores between two- and three dimensionally cultured tumor cells

Intercellular signal transfer via gap junction pores in cultured multicell spheroids of BICR/M1R-K cells decreases with increasing spheroid age. In two days old spheroids the pores allow passage of Lucifer yellow molecules. Two days later, this fluorescent dye is retained in the injected cell even though the cells are still electrically coupled. Gap junction plaques of considerable size are still found in 9 days old spheroids, when the cells are completely uncoupled. The same cells growing as monolayer cultures do not exhibit such a gradual closing of their gap junction pores: Their coupling is established at first cell contact, probably by a gradual opening of the pores, which remain open even up to 9 days in culture.