Drosophila yan has been postulated to act as an antagonist of the proneural signal mediated by the sevenless/Ras1/MAPK pathway. We have mutagenized the eight MAPK phosphorylation consensus sites of yan and examined the effects of overexpressing the mutant protein in transgenic flies and transfected S2 cultured cells. Our results suggest that phosphorylation by MAPK affects the stability and subcellular localization of yan, resulting in rapid down-regulation of yan activity. Furthermore, MAPK-mediated down-regulation of yan function appears to be critical for the proper differentiation of both neuronal and nonneuronal tissues throughout development, suggesting that yan is an essential component of a general timing mechanism controlling the competence of a cell to respond to inductive signals.

Analysis of the nucleotide sequence of the genetic locus for yeast mitochondrial RNA polymerase (RPO41) reveals a continuous open reading frame with the coding potential for a polypeptide of 1351 amino acids, a size consistent with the electrophoretic mobility of this enzymatic activity. The transcription product from this gene spans the singular reading frame. In vivo transcript abundance reflects codon usage and growth under stringent conditions for mitochondrial biogenesis and function results in a several fold higher level of gene expression than growth under glucose repression. A comparison of the yeast mitochondrial RNA polymerase amino acid sequence to those of E. coli RNA polymerase subunits failed to demonstrate any regions of homology. Interestingly, the mitochondrial enzyme is highly homologous to the DNA-directed RNA polymerases of bacteriophages T3 and T7, especially in regions most highly conserved between the T3 and T7 enzymes themselves.

The vast majority of mammalian genomes are transcribed as non-coding RNA in what is referred to as “pervasive transcription.” Recent studies have uncovered various families of non-coding RNA transcribed upstream of transcription start sites. In particular, highly unstable promoter upstream transcripts known as PROMPTs have been shown to be targeted for exosomal degradation by the nuclear exosome targeting complex (NEXT) consisting of the RNA helicase MTR4, the zinc-knuckle scaffold ZCCHC8, and the RNA binding protein RBM7. Here, we report that in addition to its known RNA substrates, ZCCHC8 is required for the targeted degradation of pervasive transcripts produced at CTCF binding sites, open chromatin regions, promoters, promoter flanking regions, and transcription factor binding sites. Additionally, we report that a significant number of RIKEN cDNAs and predicted genes display the hallmarks of PROMPTs and are also substrates for ZCCHC8 and/or NEXT complex regulation suggesting these are unlikely to be functional genes. Our results suggest that ZCCHC8 and/or the NEXT complex may play a larger role in the global regulation of pervasive transcription than previously reported.Competing Interest StatementThe authors have declared no competing interest.

Directed cell motility is at the basis of biological phenomena such as development, wound healing, and metastasis. It has been shown that substrate attachments mediate motility by coupling the cell's cytoskeleton with force generation. However, it has been unclear how the persistence of cell directionality is facilitated. We show that mRNA localization plays an important role in this process, but the mechanism of action is still unknown. In this study, we show that the zipcode-binding protein 1 transports β-actin mRNA to the focal adhesion compartment, where it dwells for minutes, suggesting a means for associating its localization with motility through the formation of stable connections between adhesions and newly synthesized actin filaments. In order to demonstrate this, we developed an approach for assessing the functional consequences of β-actin mRNA and protein localization by tethering the mRNA to a specific location-in this case, the focal adhesion complex. This approach will have a significant impact on cell biology because it is now possible to forcibly direct any mRNA and its cognate protein to specific locations in the cell. This will reveal the importance of localized protein translation on various cellular processes.

β-secretase (or BACE1) is the key enzyme in the production of β-amyloid (Aβ), which accumulates in the senile plaques characteristic for Alzheimer's disease. Consequently, the lack of BACE1 prevents β-processing of the amyloid precursor protein and Aβ production, which made it a promising target for drug development. However, the loss of BACE1 is also detrimental, leading to myelination defects and altered neuronal activity, functions that have been associated with the cleavage of Neuregulin and a voltage-gated sodium channel subunit. Here we show that the Drosophila ortholog of BACE, dBACE, is required for glial survival. Cell-specific knockdown experiments reveal that this is a non-cell autonomous function, as a knockdown of dBACE in photoreceptor neurons leads to progressive degeneration of glia in their target zone, the lamina. Interestingly, this phenotype is suppressed by the loss of the fly amyloid precursor protein (APPL), whereas a secretion-deficient form of APPL enhances the degeneration. This shows that full-length APPL in neurons promotes the death of neighboring glial cells and that β-processing of APPL is needed to prevent glial death. These results therefore not only demonstrate a novel function for an APP protein in glia, but they also show this function specifically requires regulation by β-cleavage.