Core Services in the Architecture of the National Digital Library for Science Education (NSDL)

We describe the core components of the architecture for the (NSDL) National Science, Mathematics, Engineering, and Technology Education Digital Library. Over time the NSDL will include heterogeneous users, content, and services. To accommodate this, a design for a technical and organization infrastructure has been formulated based on the notion of a spectrum of interoperability. This paper describes the first phase of the interoperability infrastructure including the metadata repository, search and discovery services, rights management services, and user interface portal facilities

Assembly of tight junctions during early vertebrate development

Tight junction formation during development is critical for embryonic patterning and organization. We consider mechanisms of junction biogenesis in cleaving mouse and Xenopus eggs. Junction assembly follows the establishment of cell polarity at 8-cell (mouse) or 2-cell (Xenopus) stages, characterized by sequential membrane delivery of constituents, coordinated by embryonic (mouse) or maternal (Xenopus) expression programmes. Cadherin adhesion is permissive for tight junction construction only in the mouse. Occludin post-translational modification and membrane delivery, mediated by delayed ZO-1 alpha+isoform expression in the mouse, provides a mechanism for completion of tight junction biogenesis and sealing, regulating the timing of blastocoel cavitation

Tight junction biogenesis during early development

The tight junction (TJ) is an essential component of the differentiated epithelial cell required for polarised transport and intercellular integrity and signalling. Whilst much can be learnt about how the TJ is constructed and maintained and how it functions using a wide range of cellular systems, the mechanisms of TJ biogenesis within developmental models must be studied to gain insight into this process as an integral part of epithelial differentiation. Here, we review TJ biogenesis in the early mammalian embryo, mainly considering the mouse but also including the human and other species, and, briefly, within the amphibian embryo. We relate TJ biogenesis to inherent mechanisms of cell differentiation and biosynthesis occurring during cleavage of the egg and the formation of the first epithelium. We also evaluate a wide range of exogenous cues, including cell–cell interactions, protein kinase C signalling, gap junctional communication, Na+/K+-ATPase and cellular energy status, that may contribute to TJ biogenesis in the embryo and how these may shape the pattern of early morphogenesi