The ins and outs of aggrecan

Aggrecan is a large and highly complex macromolecule, uniquely structured to fill space in the extracellular matrix (ECM) of cartilage. Lethal chondrodystrophies resulting from mutations in the structural gene for aggrecan demonstrate the serious consequences of the absence of aggrecan. Other chondrodystrophies are testimony to the importance of post-translational modifications.

Here, Barbara Vertel reviews the role of aggrecan in the ECM of cartilage, discusses genetic mutations affecting aggrecan and highlights intracellular features of its synthesis and processing.     

The ins and outs of translation

A report on the 2nd EMBO Conference on Protein Synthesis and Translational Control, Heidelberg, Germany, 12-16 September 2007.     

The ins and outs of nucleosome assembly

De novo nucleosome assembly coupled to DNA replication and repair in vitro involves the histone chaperone chromatin assembly factor 1 (CAF-1). Recent studies support a model in which CAF-1 can be targeted to newly synthesized DNA through a direct interaction with proliferating cell nuclear antigen (PCNA) and can act synergistically with a newly identified histone chaperone. Insights have also been obtained into mechanisms by which this CAF-1-dependent pathway can establish a repressed chromatin state.     

The ins and outs of E-cadherin trafficking

One way of controlling the activity of E-cadherin--a protein that is, simultaneously, a major cell-adhesion molecule, a powerful tumour suppressor, a determinant of cell polarity and a partner to the potent catenin signalling molecules--is to keep it on the move. During the past two decades, many insights into the fundamental role of E-cadherin in these processes have been garnered. Studies during the past five years have begun to reveal the importance of intracellular trafficking as a means of regulating the functions of E-cadherin. E-cadherin is trafficked to and from the cell surface by exocytic and multiple endocytic pathways. In this article, we survey the vesicle-trafficking machinery that is responsible for the sorting, transport, actin association and vesicle targeting of E-cadherin to regulate its movement and function during growth and development and, possibly, in cancer.     

The ins and outs of EBV infection

Epstein-Barr virus (EBV) infects almost the entire adult population of the world. The success of this virus appears to be based on its ability to infect the B cell, rather than any other cell type. We review EBV B-cell tropism, and discuss the mechanisms by which the virus may gain access to, and egress from, B cells in the normal host.     

Flowers under pressure: ins and outs of turgor regulation in development

Background

Turgor pressure is an essential feature of plants; however, whereas its physiological importance is unequivocally recognized, its relevance to development is often reduced to a role in cell elongation.

Scope

This review surveys the roles of turgor in development, the molecular mechanisms of turgor regulation and the methods used to measure turgor and related quantities, while also covering the basic concepts associated with water potential and water flow in plants. Three key processes in flower development are then considered more specifically: flower opening, anther dehiscence and pollen tube growth.

Conclusions

Many molecular determinants of turgor and its regulation have been characterized, while a number of methods are now available to quantify water potential, turgor and hydraulic conductivity. Data on flower opening, anther dehiscence and lateral root emergence suggest that turgor needs to be finely tuned during development, both spatially and temporally. It is anticipated that a combination of biological experiments and physical measurements will reinforce the existing data and reveal unexpected roles of turgor in development.     

The ins and outs of Arabidopsis embryogenesis

In this issue of Developmental Cell, Nodine and colleagues show that two related leucine-rich repeat receptor kinases, RECEPTOR-LIKE PROTEIN KINASE1 and TOADSTOOL2, are critical in establishing radial pattern in the Arabidopsis embryo (Nodine et al., 2007). Embryos lacking these kinases show replacement of outer cell fates with inner cell fates.     

The ins and outs of sphingolipid synthesis

Sphingolipids are ubiquitous components of eukaryotic cell membranes, where they play important roles in intracellular signaling and in membrane structure. Even though the biochemical pathway of sphingolipid synthesis and its compartmentalization between the endoplasmic reticulum and Golgi apparatus have been known for many years, the molecular identity of the enzymes in this pathway has only recently been elucidated. Here, we summarize progress in the identification and characterization of the enzymes, the transport of ceramide from the endoplasmic reticulum to the Golgi apparatus, and discuss how regulating the synthesis of sphingolipids might impact upon their functions.     

The ins and outs of cell-polarity decisions

The guanine-nucleotide-exchange factor Cdc24 is a critical regulator of cell polarity. Far1 is a key player in Cdc24 regulation, controlling Cdc24 activity in budding yeast by regulating its subcellular localization in response to two very different signals - one external and one internal.     

The ins and outs of Wingless signaling

Signaling through the highly conserved Wingless/Wnt pathway plays a crucial role in a diverse array of developmental processes, many of which depend upon the precise regulation of Wingless/Wnt signaling levels. Recent evidence has indicated that the intracellular trafficking of Wingless/Wnt signaling components can result in significant changes in the level of signaling. Here, we examine three mechanisms through which intracellular trafficking might regulate Wingless signaling--the degradation of Wingless, its transport and the transduction of its signal. The intracellular trafficking of several Wingless/Wnt signaling components, including LRP5, LRP6, Dishevelled and Axin, as well as the functional implications of protein localization on Wingless/Wnt signaling, will be discussed.     

The ins and outs of meiosis.

During oogenesis the oocyte is arrested in meiosis twice. First at prophase I, then a second time at metaphase I in many invertebrates and in metaphase II in the vast majority of vertebrates. Meiosis resumption is triggered by the sperm. This article examines mechanisms that cause oocytes' arrest in meiosis and how spermatozoa help the oocyte to get out of this cellular predicament. J. Exp. Zool. (Mol. Dev. Evol.) 285:226-236, 1999.