Organisms store energy for later use during times of nutrient scarcity. Excess energy is stored as triacylglycerol in lipid droplets during lipogenesis. When energy is required, the stored triacylglycerol is hydrolyzed via activation of lipolytic pathways. The coordination of lipid storage and utilization is regulated by the perilipin family of lipid droplet coat proteins [perilipin, adipophilin/adipocyte differentiation-related protein (ADRP), S3-12, tail-interacting protein of 47 kilodaltons (TIP47), and myocardial lipid droplet protein (MLDP)/oxidative tissues-enriched PAT protein (OXPAT)/lipid storage droplet protein 5 (LSDP5)]. Lipid droplets are dynamic and heterogeneous in size, location, and protein content. The proteins that coat lipid droplets change during lipid droplet biogenesis and are dependent upon multiple factors, including tissue-specific expression and metabolic state (basal vs. lipogenic vs. lipolytic). New data suggest that proteins previously implicated in vesicle trafficking, including Rabs, soluble N-ethylmaleimide sensitive factor attachment protein receptors (SNAREs), and motor and cytoskeletal proteins, likely orchestrate the movement and fusion of lipid droplets. Thus, rather than inert cytoplasmic inclusions, lipid droplets are now appreciated as dynamic organelles that are critical for management of cellular lipid stores. That much remains to be discovered is suggested by the recent identification of a novel lipase [adipocyte triglyceride lipase (ATGL)] and lipase regulator [Comparative Gene Identification-58 (CGI-58)], which has led to reconsideration of the decades-old model of lipolysis. Future discovery likely will be driven by the exploitation of model organisms and by human genetic studies.

Respiratory syncytial virus (RSV) infects polarized epithelia, which have tightly regulated trafficking because of the separation and maintenance of the apical and basolateral membranes. Previously we established a link between the apical recycling endosome (ARE) and the assembly of RSV. The current studies tested the role of a major ARE-associated protein, Rab11 family interacting protein 2 (FIP2) in the virus life cycle. A dominant-negative form of FIP2 lacking its N-terminal C2 domain reduced the supernatant-associated RSV titer 1,000-fold and also caused the cell-associated virus titer to increase. These data suggested that the FIP2 C2 mutant caused a failure at the final budding step in the virus life cycle. Additionally, truncation of the Rab-binding domain from FIP2 caused its accumulation into mature filamentous virions. RSV budding was independent of the ESCRT machinery, the only well-defined budding mechanism for enveloped RNA viruses. Therefore, RSV uses a virus budding mechanism that is controlled by FIP2.Pneumovirinae ͉ Rab11 protein ͉ virus replication ͉ virus shedding R espiratory syncytial virus (RSV) is the most common viral cause of serious lower respiratory tract illness in infants and children worldwide. RSV is a negative-sense, single-stranded RNA virus of the Paramyxoviridae family, which encodes 11 proteins. Infection is limited to the most superficial layer of polarized ciliated cells in the respiratory tract epithelium, entering through the apical surface (1, 2). Late steps of the RSV life cycle include assembly and budding of the virus, which also occur at the apical membrane in polarized cells (3).RSV virions are pleomorphic, with a spherical form varying in size from 150 to 250 nm in diameter. The filamentous form of the virus has a smaller diameter of 50 nm and can have a length from 1 to 10 microns, depending on the cell line in which virus is grown (4). Filamentous RSV has been observed budding and fusing with cells during the spread of RSV infection (5). These long filaments destabilize into spherical forms that can be similar to the size of spherical particles collected during infection (4). Other related viruses also make filamentous virions such as influenza, Ebola, and parainfluenza viruses (6,7,8). In polarized cell culture monolayers, influenza virus is predominantly filamentous, and this filamentous form has a higher specific infectivity (9). A previous analysis of the RSV cell-surface filaments in live infected cells showed that these filaments are dynamic, demonstrating rotation, directed motion, and diffusion (10).The minimal viral protein requirements for budding of RSV virus-like particles (VLPs) are fusion (F), matrix (M), nucleoprotein (N), and phosphoprotein (P) (11). The F protein follows the secretory pathway through the endoplasmic reticulum and Golgi and is directed to the apical membrane through a lipid raft-associated mechanism (12). The other viral structural proteins and the RNA genome must also traffic to the apical membrane from the cytoplasm and viral inc...

Given the ever-increasing toxic exposure ubiquitously present in our environment as well as emerging evidence that these exposures are hazardous to human health, the current rodent-based regulations are proving inadequate. In the process of overhauling risk assessment methodology, a nonrodent test organism, the zebrafish, is emerging as tractable for medium- and high-throughput assessments, which may help to accelerate the restructuring of standards. Zebrafish have high developmental similarity to mammals in most aspects of embryo development, including early embryonic processes, and on cardiovascular, somite, muscular, skeletal, and neuronal systems. Here, we briefly describe the development of these systems and then chronicle the toxic impacts assessed following chemical exposure. We also compare the available data in zebrafish toxicity assays with two databases containing mammalian toxicity data. Finally, we identify gaps in our collective knowledge that are ripe for future studies.

Rab11a, myosin Vb, and the Rab11-family interacting protein 2 (FIP2) regulate plasma membrane recycling in epithelial cells. This study sought to characterize more fully Rab11-FIP2 function by identifying kinase activities modifying Rab11-FIP2. We have found that gastric microsomal membrane extracts phosphorylate Rab11-FIP2 on serine 227. We identified the kinase that phosphorylated Rab11-FIP2 as MARK2/EMK1/Par-1B␣ (MARK2), and recombinant MARK2 phosphorylated Rab11-FIP2 only on serine 227. We created stable Madin-Darby canine kidney (MDCK) cell lines expressing enhanced green fluorescent protein-Rab11-FIP2 wild type or a nonphosphorylatable mutant [Rab11-FIP2(S227A)]. Analysis of these cell lines demonstrates a new role for Rab11-FIP2 in addition to that in the plasma membrane recycling system. In calcium switch assays, cells expressing Rab11-FIP2(S227A) showed a defect in the timely reestablishment of p120-containing junctional complexes. However, Rab11-FIP2(S227A) did not affect localization with recycling system components or the normal function of apical recycling and transcytosis pathways. These results indicate that phosphorylation of Rab11-FIP2 on serine 227 by MARK2 regulates an alternative pathway modulating the establishment of epithelial polarity.