Comparison of impact of EMCV replication on the nuclear apparatus of NIH 3T3 and HEp-2 cells

We have investigated differences between the actions of encephalomyocarditis virus (EMCV) on cytometric indices in cultured NIH 3T3 and HEp-2 cells, which are characterized by different levels of transformation. HEp-2 cells surviving 48 h after EMCV infection showed lower nuclear ploidy, reduced nuclear area, fewer nucleoli and a higher percentage of euploid cells. There was a significant increase of nucleolar/nuclear DNA 6-24 h after EMCV infection. However, EMCV had markedly different effects on NIH 3T3 cells: there was a consistent increase in population ploidy, but the average number of nucleoli and the number of euploid cells in the population remained constant. The nucleolar/nuclear DNA ratio was almost unchanged. These different viral effects might be explained by the contrasting levels of differentiation of the cultured cell lines. The number of nucleoli does not depend on the amount of nuclear DNA in either viral-infected or intact cells but on the euploidy-to-aneuploidy ratio. The ratio of the sums of the nucleolar perimeters to the nuclear perimeter increases linearly with the number of nucleoli per nucleus in both intact and virus-infected cells. In both cell lines, the amount of DNA per nucleolus decreases as the number of nucleoli increases.     

The vertebrate social behavior network: evolutionary themes and variations

Based on a wide variety of data, it is now clear that birds and teleost (bony) fish possess a core "social behavior network" within the basal forebrain and midbrain that is homologous to the social behavior network of mammals. The nodes of this network are reciprocally connected, contain receptors for sex steroid hormones, and are involved in multiple forms of social behavior. Other hodological features and neuropeptide distributions are likewise very similar across taxa. This evolutionary conservation represents a boon for experiments on phenotypic behavioral variation, as the extraordinary social diversity of teleost fish and songbirds can now be used to generate broadly relevant insights into issues of brain function that are not particularly tractable in other vertebrate groups. Two such lines of research are presented here, each of which addresses functional variation within the network as it relates to divergent patterns of social behavior. In the first set of experiments, we have used a sexually polymorphic fish to demonstrate that natural selection can operate independently on hypothalamic neuroendocrine functions that are relevant for (1) gonadal regulation and (2) sex-typical behavioral modulation. In the second set of experiments, we have exploited the diversity of avian social organizations and ecologies to isolate species-typical group size as a quasi-independent variable. These experiments have shown that specific areas and peptidergic components of the social behavior network possess functional properties that evolve in parallel with divergence and convergence in sociality.     

CD24 is expressed specifically in the nucleus pulposus of intervertebral discs

Intervertebral disc (IVD) consists of a soft gelatinous material in its center, the nucleus pulposus (NP), bounded peripherally by fibrocartilage, annulus fibrosus (AF). Despite the number of patients with IVD degeneration, gene expression analysis has not been undertaken in NP and therefore little is known about the molecular markers expressed in NP. Here, we undertook a microarray screen in NP with the other nine tissues to identify the specific cell surface markers for NP. Five membrane associating molecules out of 10,490 genes were identified as highly expressing genes in NP compared with the other tissues. Among them, we identified CD24, a glycosylphosphatidylinositol (GPI) anchor protein as a cell surface marker for NP. CD24 expression was also detected in the herniated NP and chordoma, a malignant primary tumor derived from notochordal cells, while it was absent in chondrosarcoma. Therefore, CD24 is a molecular marker for NP as well as the diseases of IVD.     

Lco1 is a novel widely expressed lamin-binding protein in the nuclear interior

A-type lamins are localized at the nuclear envelope and in the nucleoplasm, and are implicated in human diseases called laminopathies. In a yeast two-hybrid screen with lamin C, we identified a novel widely expressed 171-kDa protein that we named Lamin companion 1 (Lco1). Three independent biochemical assays showed direct binding of Lco1 to the C-terminal tail of A-type lamins with an affinity of 700 nM. Lco1 also bound the lamin B1 tail with lower affinity (2 microM). Ectopic Lco1 was found primarily in the nucleoplasm and colocalized with endogenous intranuclear A-type lamins in HeLa cells. Overexpression of prelamin A caused redistribution of ectopic Lco1 to the nuclear rim together with ectopic lamin A, confirming association of Lco1 with lamin A in vivo. Whereas the major C-terminal lamin-binding fragment of Lco1 was cytoplasmic, the N-terminal Lco1 fragment localized in the nucleoplasm upon expression in cells. Furthermore, full-length Lco1 was nuclear in cells lacking A-type lamins, showing that A-type lamins are not required for nuclear targeting of Lco1. We conclude that Lco1 is a novel intranuclear lamin-binding protein. We hypothesize that Lco1 is involved in organizing the internal lamin network and potentially relevant as a laminopathy disease gene or modifier.     

What Does the Microsporidian <Emphasis Type="Italic">E. cuniculi</Emphasis> Tell Us About the Origin of the Eukaryotic Cell?

The relationship among the three cellular domains Archaea, Bacteria, and Eukarya has become a central problem in unraveling the tree of life. This relationship can now be studied as the completely sequenced genomes of representatives of these cellular domains become available. We performed a bioinformatic investigation of the Encephalitozoon cuniculi proteome. E. cuniculi has the smallest sequenced eukaryotic genome, 2.9 megabases coding for 1997 proteins. The proteins of E. cuniculi were compared with a previously characterized set of eukaryotic signature proteins (ESPs). ESPs are found in a eukaryotic cell, whether from an animal, a plant, a fungus, or a protozoan, but are not found in the Archaea and the Bacteria. We demonstrated that 85% of the ESPs have significant sequence similarity to proteins in E. cuniculi. Hence, E. cuniculi, a minimal eukaryotic cell that has removed all inessential proteins, still preserves most of the ESPs that make it a member of the Eukarya. The locations and functions of these ESPs point to the earliest history of eukaryotes.Reviewing Editor: Dr. Manyuan Long     

Nucleocytoplasmic Shuttling of p62/SQSTM1 and Its Role in Recruitment of Nuclear Polyubiquitinated Proteins to Promyelocytic Leukemia Bodies

p62, also known as sequestosome1 (SQSTM1), A170, or ZIP, is a multifunctional protein implicated in several signal transduction pathways. p62 is induced by various forms of cellular stress, is degraded by autophagy, and acts as a cargo receptor for autophagic degradation of ubiquitinated targets. It is also suggested to shuttle ubiquitinated proteins for proteasomal degradation. p62 is commonly found in cytosolic protein inclusions in patients with protein aggregopathies, it is up-regulated in several forms of human tumors, and mutations in the gene are linked to classical adult onset Paget disease of the bone. To this end, p62 has generally been considered to be a cytosolic protein, and little attention has been paid to possible nuclear roles of this protein. Here, we present evidence that p62 shuttles continuously between nuclear and cytosolic compartments at a high rate. The protein is also found in nuclear promyelocytic leukemia bodies. We show that p62 contains two nuclear localization signals and a nuclear export signal. Our data suggest that the nucleocytoplasmic shuttling of p62 is modulated by phosphorylations at or near the most important nuclear localization signal, NLS2. The aggregation of p62 in cytosolic bodies also regulates the transport of p62 between the compartments. We found p62 to be essential for accumulation of polyubiquitinated proteins in promyelocytic leukemia bodies upon inhibition of nuclear protein export. Furthermore, p62 contributed to the assembly of proteasome-containing degradative compartments in the vicinity of nuclear aggregates containing polyglutamine-expanded Ataxin1Q84 and to the degradation of Ataxin1Q84.