Preface

Membrane traffic is a broad field that studies the complex exchange of membranes that occurs inside the cell. Protein, lipids and other molecules traffic among intracellular organelles, and are delivered to, or transported from the cell surface by virtue of membranous carriers generally referred as "transport intermediates". These carriers have different shapes and sizes, and their biogenesis, modality of transport, and delivery to the final destination are regulated by a multitude of very complex molecular machineries, which include cytoskeletal elements, signaling complexes, and lipid modifying enzymes to name a few. A concept that has clearly emerged in the last decade is that each membrane pathway does not represent a close system, but is fully integrated with all the other trafficking pathways. The precise coordination and balance of membrane trafficking is an absolute requirement to ensure the correct functioning of the cell. The aim of this book is to provide the reader with a general overview of the extent of the crosstalk among the intracellular membrane pathways.

Although this book is far from being exhaustive, it conveys some of the novel ideas and directions in the membrane trafficking field through a combination of review, research, and technical articles. The book is organized in a series of chapters that will "transport" the reader from the endoplasmic reticulum, where proteins and lipids are synthesized, to the plasma membrane, where molecules are either delivered or internalized via endocytosis. Some of the basic steps of the secretory pathway are here reviewed, such as the transport of cargo molecules from the ER to the Golgi apparatus, the sorting of transport intermediates at the Trans-Golgi Network, and the delivery of secretory vesicles to the plasma membrane. Several new aspects have been highlighted: for example, a novel role for lipids as receptors which drive protein sorting, the diversity of the sorting events that occur at the level of the Golgi apparatus, and the cross talk between exocytosis and autophagy. Moreover, an interesting example of how the knowledge of these pathways is exploited to generate novel secretory routes to direct the synthesis of bio-molecules in "cell factories" is discussed. This journey continues with an introduction to the events originated from the plasma membrane and their relationship to exocytic and signaling pathways. This area is particularly important since the precise coordination of these processes is fundamental in regulating events that affect cell motility, proliferation, and cell division, whereas their imbalance leads to pathological outcomes, such as cancer or degenerative diseases.

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I hope that the reader will find these chapters useful to get new perspectives on some of the current topics and issues in membrane trafficking, and to get a sense on the diversity of approaches and experimental systems that are used in this field.

Finally, I would like to thank all the people associated with the production of this book. First, the authors themselves for taking the time to prepare their chapters in a timely manner and in a format filled with technical details and novel and exciting concepts. It is not an easy task, and I sincerely thank them for their efforts. Second, I would like to thank Intech for the opportunity to edit this book, and its staff, that has made my job a real pleasure.

#### **Roberto Weigert Ph.D.**

Chief, Intracellular Membrane Trafficking Unit, Oral and Pharyngeal Cancer Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda USA
