Molecular chaperones, including the heat-shock proteins (Hsps), are a ubiquitous feature of cells in which these proteins cope with stress-induced denaturation of other proteins. Hsps have received the most attention in model organisms undergoing experimental stress in the laboratory, and the function of Hsps at the molecular and cellular level is becoming well understood in this context. A complementary focus is now emerging on the Hsps of both model and nonmodel organisms undergoing stress in nature, on the roles of Hsps in the stress physiology of whole multicellular eukaryotes and the tissues and organs they comprise, and on the ecological and evolutionary correlates of variation in Hsps and the genes that encode them. This focus discloses that (a) expression of Hsps can occur in nature, (b) all species have hsp genes but they vary in the patterns of their expression, (c) Hsp expression can be correlated with resistance to stress, and (d) species' thresholds for Hsp expression are correlated with levels of stress that they naturally undergo. These conclusions are now well established and may require little additional confirmation; many significant questions remain unanswered concerning both the mechanisms of Hsp-mediated stress tolerance at the organismal level and the evolutionary mechanisms that have diversified the hsp genes.

/pdf/heat-shock-proteins-molecular-chaperones-and-the-stress-p3ghklf1z7.pdf

Heat-shock proteins, molecular chaperones, and the stress response: evolutionary and ecological physiology

Chemical Diversity in the Sialic Acids and Related α-Keto Acids: An Evolutionary Perspective

Long-chain fatty acids and lipids serve a wide variety of functions in mammalian homeostasis, particularly in the formation and dynamic properties of biological membranes and as fuels for energy production in tissues such as heart and skeletal muscle. On the other hand, long-chain fatty acid metabolites may exert toxic effects on cellular functions and cause cell injury. Therefore, fatty acid uptake into the cell and intracellular handling need to be carefully controlled. In the last few years, our knowledge of the regulation of cellular fatty acid uptake has dramatically increased. Notably, fatty acid uptake was found to occur by a mechanism that resembles that of cellular glucose uptake. Thus, following an acute stimulus, particularly insulin or muscle contraction, specific fatty acid transporters translocate from intracellular stores to the plasma membrane to facilitate fatty acid uptake, just as these same stimuli recruit glucose transporters to increase glucose uptake. This regulatory mechanism is important to clear lipids from the circulation postprandially and to rapidly facilitate substrate provision when the metabolic demands of heart and muscle are increased by contractile activity. Studies in both humans and animal models have implicated fatty acid transporters in the pathogenesis of diseases such as the progression of obesity to insulin resistance and type 2 diabetes. As a result, membrane fatty acid transporters are now being regarded as a promising therapeutic target to redirect lipid fluxes in the body in an organ-specific fashion.

/pdf/membrane-fatty-acid-transporters-as-regulators-of-lipid-2mfmr8lj1k.pdf

Membrane Fatty Acid Transporters as Regulators of Lipid Metabolism: Implications for Metabolic Disease

THE ability of cells to interact and communicate is a biological phenomenon that developed with the evolution of multicellular organisms. The cell-cell interactions that have evolved are essential for the survival of both simple organisms such as dictyostelium and complex organisms such as mammals. These cellular associations allow an organism to develop capacities that are greater than the simple sum of their individual parts. As early as 1878, Claude Bernard proposed that the “milieu interieur” (i.e. internally produced fluid environment) and a cybernetic-like control system (i.e. cell-cell interactions and communication) in multicellular organisms are needed to adaptively regulate the growth, development, and maintenance of normal tissue function (1, 2). The experimental analysis of cellular interactions was initiated with the investigation of cell aggregation in simple organisms such as sponges (3, 4) and progressed into the areas of embryology (5) and cell biology (6, 7). Analysis of cell biology on ...

Cell-Cell Interactions in the Testis

Gap junctions form channels between adjacent cells. The core proteins of these channels are the connexins. Regulation of gap junction communication (GJC) can be modulated by connexin-associating proteins, such as regulatory protein phosphatases and protein kinases, of which c-Src is the best-studied. Structural proteins, notably zona occludens-1 (ZO-1) and microtubules, have been found recently at gap junctions. Along with the expansion of the list of connexin-associating proteins, reports have appeared that suggest that connexins might have additional roles in addition to their channel function, such as transcriptional and cytoskeletal regulation. Here, gap junction interacting proteins are reviewed and their function is addressed. The striking similarity of proteins present at the cytoplasmic face of tight junctions, adherens junctions and gap junctions and their possible role in gene transcription and cytoskeletal anchorage is highlighted.

/pdf/gap-junctions-and-connexin-interacting-proteins-2hujkvc76u.pdf

Gap junctions and connexin-interacting proteins

A cytoskeletal protein unique to lens fiber cell differentiation

A biochemically active conjugate of calmodulin and tetramethylrhodamine isothiocyanate (CaM-RITC) was synthesized. When incubated with sections of chick lens, this conjugate bound to the surface membranes of lens fiber cells in the presence of absence of calcium. Incubation of lens sections with antibodies to gap junction protein of lens completely blocked the binding of the conjugate to cell membranes, whereas serum from nonimmunized animals or antibodies to others lens proteins reduced the binding only slightly. By means of a gel overlay procedure, 125I-labeled calmodulin was found to bind to the gap junction protein of lens, also in a calcium-independent manner. These results support the concept that calmodulin may interact with and regulate gap junctions in living cells.

Calmodulin binds to chick lens gap junction protein in a calcium-independent manner

The cytoskeleton of chick lens cells

Cultures of Sertoli cells were treated with freshly isolated, intact germ cells to determine if germ cells were capable of influencing Sertoli cell function. By using two-dimensional polyacrylamide gel electrophoresis and autoradiography, germ cells were found to increase several-fold the incorporation of [32P]orthophosphate into two phosphoproteins (which we term germ cell-dependent phosphoproteins 1 and 2 or GCl and GC2) of Sertoli cells. Increased phosphorylation of GCl and GC2 was rapid, germ cell dose dependent, and calcium dependent. The increased phosphorylation of GCl appears to involve calmodulin- dependent protein kinase, while phosphorylation of GC2 appears to involve the activation of calcium/phospholipid-dependent protein kinase (protein kinase C). Medium conditioned by germ cells was capable of eliciting the same response in Sertoli cells. Germ cells had no effect on the phosphorylation of proteins in Chinese hamster ovarian cells, but did result in increased phosphorylation of a protein in ...

Germ cell stimulation of Sertoli cell protein phosphorylation

The early embryonic development and expression patterns of the eye lens specific cytoskeletal proteins, CP49 and CP95, were determined for the chick and were found to be similar in both human and mouse. These proteins, as well as their homologs in other species, are obligate polymerization partners which form unique filamentous structures termed “beaded filaments.” CP49 and CP95 appeared as protein products after 3 days of embryonic development in the chick during the elongation of primary fiber cells. Although limited data were obtained for human embryos at these early developmental timepoints, they were consistent with the interpretation that the up-regulation of these lens specific proteins began only after the initiation of lens vesicle closure. In situ hybridization with the mouse lens confirmed that message levels for beaded filament proteins were greatly elevated in differentiating primary fiber cells. Nuclease protection assays established that mRNA levels for CP49 remained relatively constant while CP95 mRNA levels increased once the process of secondary fiber formation was under way. Although present in relatively low abundance, the mRNA for a unique splice variant of CP49, CP49INS, was also detected early in embryonic development and into adulthood. Peptide-specific antibodies directed against unique predicted sequences were able to confirm the protein expression of CP49INS in both embryonic and adult chick lens cells. These data present the first detailed study of the expression of CP49 and CP95 during early lens development. They suggest that the up-regulated expression of CP49 and CP95 could serve as pan-specific markers for all vertebrate lens fiber development. Anat Rec 258:25–33, 2000. © 2000 Wiley-Liss, Inc.

Up-regulation of novel intermediate filament proteins in primary fiber cells: an indicator of all vertebrate lens fiber differentiation?

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