About the Cover.

Abstract

Next article FreeAbout the CoverPDFPDF PLUSFull Text Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinked InRedditEmailQR Code SectionsMoreCoverMany organisms, including fish, amphibians, cephalopods, insects, and crustaceans, use color changes for a variety of functions such as camouflage, signaling to other animals, protection against ultraviolet radiation, and even regulation of body surface temperature. These adaptive strategies are particularly well developed among decapod crustaceans, which have evolved complex mechanisms based on the movement of pigment granules within specialized effectors. On the cover, a computer model depicts, in three dimensions, the spatial relationships among the principal structural components of the pigment transport apparatus. Above the model, in the inset, is a photomicrograph of a chromatosome from the ovary of the freshwater shrimp Macrobrachium olfersi. Chromatosomes, which are aggregates of individual pigment-containing cells, or chromatophores, are found within the integumental epidermis and on the fibrous capsules surrounding the internal organs; the one shown here contains red pigment granules in the dispersed state.Molecular motors such as myosin and kinesin use the chromatophore cytoskeleton, which consists of microfilaments and microtubules, as a guidance system to power the cytoplasmic translocation of the colored pigment granules between the states of pigment dispersion and aggregation, resulting in adaptive color changes. Other less well-studied organelles like the smooth endoplasmic reticulum are also important in this dynamic process. In the model, large membrane-bounded pigment granules (red) and small carotenoid granules (yellow-green) are shown enmeshed by the cisternae (blue) of the smooth endoplasmic reticulum and interspersed among microfilaments (green rods) and a microtubule (light orange rod).On pages 111–121 of this issue, Robert Boyle and John McNamara develop the idea that a structural continuum formed between the pigment granules and the well-developed smooth endoplasmic reticulum in freshwater shrimp ovarian chromatophores constitutes an elastic spring-matrix. Using Robert Hooke’s and George Stokes’ original equations, applied to quantifiable kinetic properties of pigment translocation in vitro, these authors show that the pigment spring-matrix behaves like a deformable resilient spring: it stores kinetic energy during pigment aggregation when the spring is compressed and releases it during pigment dispersion when the spring is stretched. They further model these mechanical properties, comparing their empirical measurements with mathematically derived predictions, and find good agreement and support for the idea that the chromatophore cytoplasm does indeed behave like a spring, modulated by the opposing forces generated by the molecular motors. This idea may advance current thinking on a variety of intracellular processes that employ the cytoskeletal-based translocation of cytoplasmic cargos.Credits: Photomicrograph, John McNamara and Márcia Ribeiro (University of São Paulo); computer-generated image, Robert Boyle (Rio Grande University Foundation); cover layout, Beth Liles (Marine Biological Laboratory) Next article DetailsFiguresReferencesCited by The Biological Bulletin Volume 214, Number 2April 2008 Published in association with the Marine Biological Laboratory Article DOIhttps://doi.org/10.1086/BBLv214n2cover Views: 157 © 2008 by Marine Biological Laboratory. All rights reserved.PDF download Crossref reports no articles citing this article.