Dosage compensation equalizes the expression of sex-linked genes between males and females. Most genes on the X chromosome of male Drosophila are transcribed at an increased level, contributing to compensation. The roX1 and roX2 genes produce non-coding transcripts that localize along the X-chromosome of male flies. Although lacking sequence similarity, they are necessary but redundant components of a system that up-regulates gene expression. Simultaneous mutation of both roX genes disrupts the X-limited distribution of proteins that modify chromatin to enhance gene expression. We have generated and characterized loss of function roX1 alleles that display a continuum of activity. Those that support intermediate male survival have strikingly reduced RNA accumulation, while alleles with minor contributions to male viability typically lack detectable transcript accumulation. Severely mutated roX1 alleles retain some ability to direct modifying proteins to the X chromosome. This ability predicts the level of male survival that each allele supports. This points to a peripheral or transient role for roX in the RNA and protein complex that binds to and regulates the X chromosome.

SUMMARY Tau is a microtubule-associated protein whose function has been investigated primarily in neurons. Recently, tau expression has been correlated with increased drug resistance in various cancers of non-neuronal tissues. In this report, we investigate the tau expressed in cancerous prostate lines ALVA-31, DU 145, and PC-3. Prostate cancer tau is heat-stable and highly phosphorylated, containing many of the modifications identified in Alzheimer’s Disease brain tau. RT-PCR and phosphatase treatment indicated that all six alternatively spliced adult brain tau isoforms are expressed in ALVA-31 cells and isoforms containing exon 6 as well as high molecular weight tau isoforms containing either exon 4A or a larger splice variant of exon 4A are also present. Consistent with its hyperphosphorylated state, a large proportion of ALVA-31 tau does not bind to microtubules, as detected by confocal microscopy and biochemical tests. Finally, endogenous ALVA-31 tau can interact with the p85 subunit of phosphatidylinositol 3-kinase, as demonstrated by co-immunoprecipitations and in vitro protein binding assays. Our results suggest that tau in prostate cancer cells does not resemble that from normal adult brain and support the hypothesis that tau is a multifunctional protein.

Over the course of an infection, many Gram-negative bacterial pathogens use complex nanomachines to directly inject tens to hundreds of proteins (effectors) into the cytosol of infected host cells. These effectors rewire processes to promote bacterial replication and spread. The roles of effectors in pathogenesis have traditionally been investigated by screening for phenotypes associated with their absence, a top-down approach that can be limited, as effectors often act in a functionally redundant or additive manner. Here we describe a synthetic -based bottom-up platform to conduct gain-of-function screens for roles of individual effectors in pathogenesis. As proof of concept, we screened for effectors that limit cell death induced on cytosolic entry of bacteria into epithelial cells. Using this platform, in addition to OspC3, an effector known to inhibit cell death via pyroptosis, we have identified OspD2 and IpaH1.4 as cell death inhibitors. In contrast to almost all type III effectors, OspD2 does not target a host cell process, but rather regulates the activity of the type III secretion apparatus limiting the cytosolic delivery (translocation) of effectors during an infection. Remarkably, by limiting the translocation of a single effector, VirA, OspD2 controls the timing of epithelial cell death via calpain-mediated necrosis. Together, these studies provide insight into the intricate manner by which effectors interact to establish a productive intracytoplasmic replication niche before the death of infected epithelial cells.

Microtubule-associated protein tau has long been known for its ability to promote microtubule assembly. A less known feature of tau is its existence as a non-microtubule associated protein. Here we review the interactions of tau with other proteins, some of which interact with the microtubule binding repeat region of tau. The tau interactions with Fyn and with Pin1 have attracted the most attention and both interactions have been thought to have a role in Alzheimer's disease. The fact that tau has unknown cellular functions is further evidenced by its involvement in cell cycle activated neurodegeneration. One possible route for additional investigations stems from the presence of tau in non-neuronal cells where its characteristics have been largely unknown, although there has been a correlation between tau levels and the response of some cancer cells to microtubule-targeting chemotherapy drugs. Our studies of prostate cancer cells indicate that these cells can provide a system with phosphorylated adult tau for functional studies. In fact, structural similarities exist between Alzheimer's disease tau and prostate cancer cell tau, raising the possibility that new tau functions uncovered in prostate cancer cells will have relevance to Alzheimer's disease.