Seminars in Developmental Biology最新文献

Skeletal muscle forms from proliferating myoblasts that differentiate, fuse into multinucleate myofibers, assemble a contractile apparatus, and form synapses with motor neurons. Proteins mediating both cell-cell and cell-matrix adhesion, including extracellular matrix proteins, integrins, cadherins, members of the immunoglobulin family, and the dystrophin-containing glycoprotein complex, are expressed by skeletal muscle and play important roles in muscle differentiation. Here, we review what is known about the function of various adhesion molecules in four major steps of skeletal muscle development: differentiation, fusion, myofibrillogenesis and synaptogenesis.

The outer surfaces of eukaryotic cells are covered with a dense and complex array of sugar chains (oligosaccharides). Most are found attached to other macromolecules, yielding glycoconjugates such as glycoproteins and glycolipids. Given their location and structural complexity, it is natural to predict their involvement in cell-cell interactions. Several examples of such interactions have been defined in animal systems. Since the expression of many oligosaccharides is tissue-specific and developmentally regulated, they may also be involved in embryonic development. Genetic evidence in favor of this notion has recently been obtained. This article provides a perspective on glycosylation in vertebrate development and experimental approaches towards elucidating oligosaccharide function.

Skeletal muscle fibers are specialized at the site of the neuromuscular synapse, and this polarity is acquired during development and maintained in the adult as a consequence of inductive interactions between nerve and muscle. This review summarizes recent experiments which demonstrate that two different signalling pathways, a transcriptional pathway and a post-translational pathway, have an important role in the formation and maintenance of the neuromuscular synapse and mediate the induction of polarity in skeletal muscle fibers.

Polarity and pattern of the Drosophila egg and embryo are initially established by maternal factors present during oogenesis and early embryogenesis. Four different maternal activities are needed to determine dorsal-ventral, anterior, posterior and terminal cell fates in the embryo. This review summarizes the emerging molecular pathways which lead from the determination of the oocyte to differential gene expression in embryonic cells along the antero-posterior and dorso-ventral axes.

Asymmetrical cellular organization, cell polarity, is fundamental to the development of multicellular organisms from egg to adult. Budding yeast (Saccharomyces cerevisiae) provides the opportunity to study the mechanisms responsible for producing an axis of polarity in a spatially regulated manner. In yeast, a number of genes are known which specifically affect either the orientation or the assembly of a polarity axis. Just as for other basic cellular functions, the mechanisms controlling cell polarity in yeast likely will be shared by multicellular organisms.

The bacterium Caulobacter crescentus generates two distinct progeny cells, a motile swarmer cell and a sessile stalked cell, at every cell division. The dramatic morphological and physiological differences between the progeny are expressed in the predivisional cell prior to separation. We review recent work examining mechanisms responsible for differentiation of the incipient swarmer and stalked cell compartments. These include differential transcription of the newly replicated chromosomes, and targeting of proteins to specific poles. The biosynthesis of the polar flagellum is emphasized as a model for studying these processes. Hypotheses concerning the role of the cell poles in expression of asymmetry are discussed.

Early mammalian and Drosophila embryos share the ability to generate epithelial cells whose plasma membranes are divided into two non-identical domains. In the past several years, much has been learned about the cellular and molecular mechanisms involved in converting non-polar embryonic cells into polarized epithelia. A comparison of these processes in mammals and Drosophila reveals important differences as well as fundamental similarities. Many of the molecules required to generate and maintain epithelial polarity appear to be shared by both systems.

Caveolae are 50–100 nm invaginations that represent a sub-compartment of the plasma membrane. Recent studies have implicated these membranous structures in: (1) transcytosis of macromolecules (such as LDL and AGEs) across capillary endothelial cells; (2) potocytic uptake of small molecules via GPI-linked receptors coupled with an unknown anion transport protein; (3) certain transmembrane signalling events; and (4) polarized trafficking of GPI-linked proteins in epithelial cells. Biochemical isolation and characterization of these domains reveals the molecular components that could perform these diverse functions: scavenger receptors for oxidized LDL and AGEs, namely CD 36 and RAGE, respectively (transcytosis); plasma membrane porin (potocytosis); heterotrimeric G-proteins and Src-like kinases (signalling); and Rap GTPases (cell polarity). As such, these findings have clear implications for understanding the molecular pathogenesis of several human diseases — including atherosclerosis, diabetic vascular complications, and cancerous cell transformations.

We make two main points about the present and the future of the study of pattern formation, which is perhaps the most interesting problem in modern developmental biology. One is that a complete understanding of a developing organism will require the integration of knowledge from a wide variety of disciplines. Our other main point is the importance of comparing organisms to find universal solutions. Here we compare two dictyostelids that have somewhat different development, to point a way toward understanding how fundamental mechanisms can vary to produce altered shapes.