Cell commitment in the ectoderm of Drosophila melanogaster.
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When submitted to a heat-shock, mouse embryonal carcinoma (EC) and fibroblast cells show very different behavior. All the EC cells so far analyzed express very high levels of several heat-shock proteins (HSP) in the absence of stress and independent of their origin and culture conditions. In such cells, the 89-kd, 70-kd and 59-kd HSP are the most prominent proteins after actin. In addition, the 89-kd and 59-kd HSP are not stimulated by an arsenite shock in contrast to what is observed with fibroblasts or cells of the parietal yolk sac type. Arsenite induces the synthesis of a 105-kd polypeptide in fibroblasts but not in EC cells. In vitro differentiation of F9 cells induced by retinoic acid and dibutyryl cAMP is accompanied by a decrease in the spontaneous relative abundance of HSP and restores the arsenite-induced synthesis of the 105-kd polypeptide. EC cells are usually believed to be similar to inner cell mass cells of mouse blastocyst. Furthermore, data in the literature together with our own results suggest that the same three HSP are also spontaneously expressed in high amounts in the early mouse embryo.
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In vertebrates, there are six or more copies of genes related to the Drosophila pattern formation homeodomain gene Distal-less. Among this family, Dlx3 and Dlx5 share extensive sequence homology and have similar, but distinctive, expression patterns, suggesting that these two factors may have substantially redundant developmental functions. Here we show that at the earliest phases of embryogenesis in Xenopus, there are significant differences between Dlx3 and Dlx5 expression and that this correlates with different functions in the restriction of neural crest and neural plate boundaries, respectively.
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Several aspects of leg development in the moth Manduca sexta were examined using the homeotic mutation Octopod (Octo). This mutation causes a transformation of the ventral epidermis of the first abdominal segment (A1) to that of the third thoracic segment (T3), resulting in the presence of thoracic-like legs on A1. The degree of transformation of A1 is variable, ranging from bumps on the cuticle to fully segmented thoracic-like legs. In the normal thoracic legs, clusters of undifferentiated cells known as differentiation centers are located around the coxal-trochanteral, femoral-tibial, and tibial-tarsal joints. The adult thoracic legs develop from the differentiation centers at metamorphosis. The homeotic legs of the Octopod larvae also have differentiation centers at comparable positions in the homeotic leg. As a result, the number of leg segments in a mutant adult is correlated with the number of segments and differentiation centers that animal had in its larval homeotic leg. Our data suggest that the differentiation center located at the coxal-trochanteral joint forms the adult coxa and trochanter, the center at the larval femoral-tibial joint the adult femur and tibia, and the differentiation center at the larval tibial-tarsal joint the adult tarsus. Homeotic larval legs which include at least a femur have supernumerary muscles, while adult homeotic legs rarely show discrete muscle. The homeotic larval muscles appear to have thoracic identities, based on their attachment points and the timing of their degeneration at the larval-pupal transition. They are innervated by a motoneuron that is normally present in A1 where it innervates the ventral lateral external muscle (VLE). In mutant animals, the same motoneuron innervates all of the homeotic muscles and the VLE. We consider possible mechanisms underlying the development of homeotic muscles and their innervation. At the larval-pupal transition, the VLE in mutant animals degenerates at its normal time, which is 3 days after the degeneration of the homeotic muscles. Thus, despite their common innervation, the two muscle types degenerate according to their own schedules, indicating that the developmental fates of the muscles are not dictated by their innervating neuron but are intrinsic to the muscles themselves.
A number of traditional techniques have been used to examine epithelial-mesenchymal interactions; they remain to this day the only means to examine the problems of tissue interactions. Problems at the tissue level of organization require that the approaches to these problems ask questions and use techniques that address the issues of tissue organization and cellular morphology in the context of three-dimensional organization. Manipulating the embryo is exactly that--manipulating a three-dimensional organized organism that must express its differentiated functional organs and organ systems. When the parallel and correlative studies of cell biological function achieve new insights, they will have to be tested in terms of the cellular response at the tissue level of organization.
Five new casses of ectrodactyly are described. Two patients have the syndrome of ectrodactyly, extodermal dysplasia, and clefting (EEC). In one patient with the EEC syndrome, the disorder seems to represent a new mutation. One woman with isolated ectrodactyly has a daughter with the EEC syndrome. The variation in the clinical expression of this disorder among affected members of the same family makes it difficult to determine whether there may be several mutant alleles responsible for ectrodactyly and its related manifestations.