BCR-mediated apoptosis associated with negative selection of immature B cells is selectively dependent on Pten

The molecular basis of B cell receptor (BCR)-induced apoptosis during the negative selection of immature B cells is largely unknown. We use transitional immature B cells that are highly susceptible to BCR-induced apoptosis to show that Pten is selectively required for BCR-mediated initiation of the mitochondrial death pathway. Specifically, deleting Pten, but not other pro-apoptotic molecules, abrogates BCR-elicited apoptosis and improves viability in wild-type immature B cells. We further identify a physiologically and significantly higher intracellular Pten level in immature B cells, as compared to mature B cells, which is responsible for low AKT activity and the propensity towards death in immature B cells. Restoration of AKT activity using a constitutive form of AKT or reduction of Pten to a level comparable with that seen in mature B cells rescues immature B cells from BCR-induced apoptosis. Thus, we provide evidence that Pten is an essential mediator of BCR-induced cell death, and that differential regulation of intracellular Pten levels determines whether BCR ligation promotes cell death or survival. Our findings provide a valuable insight into the mechanisms underlying negative selection and clonal deletion of immature B cells.     

Stephanorhinus hundsheimensis (Mammalia,Rhinocerotidae) from the late early Pleistocene deposits of the Denizli Basin (Anatolia,Turkey)

Pleistocene rhinoceroses are poorly documented in Turkey where they have been reported only from the late early Pleistocene (1.3–1.1 Ma) travertine deposits of the Denizli Basin. In this work, new rhinoceros remains collected from this basin are assigned to a relatively large-sized Stephanorhinus hundsheimensis on the basis of their morphology and morphometry. The first Turkish record of this species is approximately coeval with the first appearance of S. hundsheimensis in Europe, chronologically referred to the late early Pleistocene, ca. 1.2 Ma. During that time, S. etruscus still survived in Iberian Peninsula, central Italy and Dacian Basin. The presence of two successive evolutionary morphs for S. hundsheimensis during the Pleistocene is not confirmed.     

Downstream of kinase, p62(dok), is a mediator of Fc gamma IIB inhibition of Fc epsilon RI signaling

The low-affinity receptor for IgG, Fc gamma RIIB, is expressed widely in the immune system and functions to attenuate Ag-induced immune responses. In mast cells, coaggregation of Fc gamma RIIB with the high-affinity IgE receptor, Fc epsilon RI, leads to inhibition of Ag-induced degranulation and cytokine production. Fc gamma RIIB inhibitory activity requires a conserved motif within the Fc gamma RIIB cytoplasmic domain termed the immunoreceptor tyrosine-based inhibition motif. When coaggregated with an activating receptor (e.g., Fc epsilon RI, B cell Ag receptor), Fc gamma RIIB is rapidly phosphorylated on tyrosine and recruits the SH2 domain-containing inositol 5-phosphatase (SHIP). However, the mechanisms by which SHIP mediates Fc gamma RIIB inhibitory function in mast cells remain poorly defined. In this report we demonstrate that Fc gamma RIIB coaggregation with Fc epsilon RI stimulates enhanced SHIP tyrosine phosphorylation and association with Shc and p62(dok). Concurrently, enhanced p62(dok) tyrosine phosphorylation and association with RasGAP are observed, suggesting that SHIP may mediate Fc gamma RIIB inhibitory function in mast cells via recruitment of p62(dok) and RasGAP. Supporting this hypothesis, recruitment of p62(dok) to Fc epsilon RI is sufficient to inhibit Fc epsilon RI-induced calcium mobilization and extracellular signal-regulated kinase 1/2 activation. Interestingly, both the amino-terminal pleckstrin homology and phosphotyrosine binding domains and the carboxyl-terminal proline/tyrosine-rich region of p62(dok) can mediate inhibition, suggesting activation of parallel downstream signaling pathways that converge at extracellular signal-regulated kinase 1/2 activation. Finally, studies using gene-ablated mice indicate that p62(dok) is dispensable for Fc gamma RIIB inhibitory signaling in mast cells. Taken together, these data suggest a role for p62(dok) as a mediator of Fc gamma RIIB inhibition of Fc epsilon RI signal transduction in mast cells.     

Expression of gp20, a human sperm antigen of epididymal origin, is reduced in spermatozoa from subfertile men

gp20, a sialylglycoprotein of human sperm homologous to CD52, is present everywhere on the surface of the freshly ejaculated sperm but is prevalently localized in the equatorial region of the head of capacitated sperm. In the present study, we confirmed this feature on large scale and correlated equatorial exposure of the antigen to the presence of serum albumin (SA) in the capacitation medium. Furthermore, we analyzed the relationship between the presence of the antigen and its equatorial exposure after capacitation and fertility, by comparing immunostaining for gp20 in the motile fraction of spermatozoa from fertile and subfertile men. A significantly higher percentage of nonimmunostained spermatozoa before capacitation (38.5% +/- 23 vs. 12% +/- 7, P < 0.0001) and a lower increase in the percentage of sperm with equatorial localization after capacitation (19.3% +/- 25 vs. 34.6% +/- 22, P = 0.039) were observed in subfertile men (n = 60) compared to fertile men (n = 15). In the whole study group, a positive correlation was also found between the percentage of spermatozoa exhibiting equatorial localization in capacitated samples and normal head forms (R = 0.50; P < 0.0001).     

Promyelocytic leukemia protein mediates interferon-based anti-herpes simplex virus 1 effects

Herpes simplex virus (HSV) 1 disaggregates the nuclear domain 10 (ND10) nuclear structures and disperses its organizing promyelocytic leukemia protein (PML). An earlier report showed that ectopic overexpression of PML precludes the disaggregation of ND10 but has no effect on viral replication. PML has been reported to mediate the effects of interferon (IFN) and viral mutants lacking ICP0 (Delta alpha 0 mutants). To test the hypothesis that HSV disaggregates ND10 structures and disperses PML to preclude IFN-mediated antiviral effects, we tested the accumulation of viral proteins and virus yields from murine PML(+/+) and PML(-/-) cells mock treated or exposed to IFN-alpha, IFN-gamma, or both and infected with the wild-type or Delta alpha 0 mutant virus. We report the following results. (i) The levels of growth of wild-type and mutant viruses and of accumulation of viral proteins were not significantly different in untreated PML(+/+) and PML(-/-) cells. (ii) Major effects of IFN-alpha and -gamma were observed in PML(+/+) cells infected with the Delta alpha 0 mutant virus, and more minor effects were observed in cells infected with the wild-type virus. The effects of the IFNs on either wild-type or the mutant virus in PML(-/-) cells were minimal. (iii) The mixture of IFN-alpha and -gamma was more effective than either IFN alone, but again, the effect was more drastic in PML(+/+) cells than in PML(-/-) cells. We concluded that the anti-HSV state induced by exogenous IFN is mediated by PML and that the virus targets the ND10 structures and disseminates PML in order to preclude the establishment of the antiviral state induced by IFNs.