Discovery of ultracompact dwarf galaxies in the Virgo Cluster

We have discovered nine ultracompact dwarf galaxies (UCDs) in the Virgo Cluster, extending samples of these objects outside the Fornax Cluster. Using the Two Degree Field (2dF) multifiber spectrograph on the Anglo-Australian Telescope, the new Virgo members were found among 1500 color-selected, starlike targets with 16: 0 < b(j) < 20.2 in a 2 degrees diameter field centered on M87 (NGC 4486). The newly found UCDs are comparable to the UCDs in the Fornax Cluster, with sizes less than or similar to 100 pc, -12.9 < M-B < -10.7, and exhibiting red absorption-line spectra, indicative of an older stellar population. The properties of these objects remain consistent with the tidal threshing model for the origin of UCDs from the surviving nuclei of nucleated dwarf elliptical galaxies disrupted in the cluster core but can also be explained as objects that were formed by mergers of star clusters created in galaxy interactions. The discovery that UCDs exist in Virgo shows that this galaxy type is probably a ubiquitous phenomenon in clusters of galaxies; coupled with their possible origin by tidal threshing, the UCD population is a potential indicator and probe of the formation history of a given cluster. We also describe one additional bright UCD with M-B = -12.0 in the core of the Fornax Cluster. We find no further UCDs in our Fornax Cluster Spectroscopic Survey down to bj 19.5 in two additional 2dF fields extending as far as 3 degrees from the center of the cluster. All six Fornax bright UCDs identified with 2dF lie within 0.degrees 5 (projected distance of 170 kpc) of the central elliptical galaxy NGC 1399.

The subcellular fractionation properties and function of insulin receptor substrate-1 (IRS-1) are independent of cytoskeletal integrity

Efficient insulin action requires spatial and temporal coordination of signaling cascades. The prototypical insulin receptor substrate, IRS-1 plays a central role in insulin signaling. By subcellular fractionation IRS-1 is enriched in a particulate fraction, termed the high speed pellet (HSP), and its redistribution from this fraction is associated with signal attenuation and insulin resistance. Anecdotal evidence suggests the cytoskeleton may underpin the localization of IRS-1 to the HSP. In the present study we have taken a systematic approach to examine whether the cytoskeleton contributes to the subcellular fractionation properties and function of IRS-1. By standard microscopy or immunoprecipitation we were unable to detect evidence to support a specific interaction between IRS-1 and the major cytoskeletal components actin (microfilaments), vimentin (intermediate filaments), and tubulin (microtubules) in 3T3-L1 adipocytes or in CHO.IR.IRS-1 cells. Pharmacological disruption of microfilaments and microtubules, individually or in combination, was without effect on the subcellular distribution of IRS-1 or insulin-stimulated tyrosine phosphorylation in either cell type. Phosphorylation of Akt was modestly reduced (20-35%) in 3T3-L1 adipocytes but not in CHO.IR.IRS-1 cells. In cells lacking intermediate filaments (Vim(-/-)) IRS-1 expression, distribution and insulin-stimulated phosphorylation appeared normal. Even after depolymerisation of microfilaments and microtubules, insulin-stimulated phosphorylation of IRS-1 and Akt were maintained in Vim-/- cells. Taken together these data indicate that the characteristic subcellular fractionation properties and function of IRS-1 are unlikely to be mediated by cytoskeletal networks and that proximal insulin signaling does not require an intact cytoskeleton. (c) 2006 Elsevier Ltd. All rights reserved.

Unicellular pheromone glands of the pentatomid bug Nezara viridula (Heteroptera : Insecta): Ultrastructure, classification, and proposed function

Male Nezara viridula produce sex pheromones from many independent single cells, each with a duct that opens onto the ventral abdominal surface. Despite the presence of along duct and an associated end complex (in the form of a cupule and microvillus saccule), the structural organization of the cells that comprise the gland conform to Class 1 epidermal gland cell classification : a single cell surrounds the entire secretory complex. Each cuticular cupule contains a central bed of filaments and opens into a narrow tubular ductule that leads from the base of the cupule through the epidermis to the cuticle to open externally as a pore. The cuticle of the cupule is continuous with that of the ductule and has the appearance of three layers, although the inner (middle) layer may be a gap formed during construction of the complex. In young adult males, just molted, the ultrastructure of the cells and their inclusions indicate that they are not active. The region of the cell that is distal to the abdominal cuticle is reduced and the proximal region, surrounding the duct, is enlarged when compared with sexually mature (3-4 weeks old) adult males. At maturity the pheromone cells are enlarged distally around the cupule, but are reduced to a narrow sleeve proximally, around the ductule. Two characteristic cell profiles are evident, based on the shape of the cupule and the organelle content. Type A shows a broad opening to the cupule, an abundance of mitochondria, and few vesicular bodies. Type B has an elongated, narrow, vase-like opening to the cupule, few mitochondria, and numerous vesicular bodies. Type B cells are smaller and more abundant than Type A. Distribution within the epidermal layer also differs. It is likely that the different types represent cells producing different secretion profiles. However, the secretions retained by the standard fixation protocol within mature cells of both types look similar and appear to collect as crystalline bodies within the lumen. This may represent a common storage mechanism.