IsomiRs have functional importance.

Since the inception of deep sequencing, isomiRs are consistently observed to be produced by most miRNA genes in a variety of cell types. IsomiRs appear as a variation in length from the canonical sequence annotated in miRBase, due to an addition or deletion of one or more nucleotides at the 5(') or 3(') ends or both. As the seed sequence is located at the 5(') end of the microRNA, the target mRNA will be theoretically different. Therefore, 5(')isomiRs might potentially target a new set mRNA compared to their canonical counterpart. This article gives an overview of investigations that explored the functional potential of isomiRs such as their ability to incorporate into Argonaute protein, the differential expression of isomiRs in various tissue types and cell lines, and the differences of mRNA targets between isomiR and its canonical microRNA. In addition, this article provides a brief introduction of RNA sponges as a potential way to inhibit isomiRs.

Lentiviral vector transduction of spermatozoa as a tool for the study of early development.

Spermatozoa and lentiviruses are two of nature's most efficient gene delivery vehicles. Both can be genetically modified and used independently for the generation of transgenic animals or gene transfer/therapy of inherited disorders. Here we show that mature spermatozoa can be directly transduced with various pseudotyped lentiviral vectors and used in in vitro fertilisation studies. Lentiviral vectors encoding Green Fluorescent Protein (GFP) were shown to be efficiently processed and expressed in sperm. When these transduced sperm were used in in vitro fertilisation studies, GFP expression was observed in arising blastocysts. This simple technique of directly transducing spermatozoa has potential to be a powerful tool for the study of early and pre-implantation development and could be used as a technique in transgenic development and vertical viral transmission studies.

Efficient generation of transgenic mice by lentivirus-mediated modification of spermatozoa.

Transgenic technologies conventionally rely on the oocyte as a substrate for genetic modification. Owing to their accessibility, however, male germ cells, including mature sperm, have material advantages for use in transgenesis. Here we have exploited lentiviruses to generate transgenic animals via the male germline. When pseudotyped lentiviral vectors encoding green fluorescent protein (GFP) were incubated with mouse spermatozoa, these sperm were highly successful in producing transgenics. Lentivirally transduced mouse spermatozoa were used in in vitro fertilization (IVF) studies, and when followed by embryo transfer, ≥ 42% of founders were found to be transgenic for GFP. Inverse PCR strategy for integration site analysis demonstrated integration of at least 1 or 2 copies of GFP in the transgenics, mapping to different chromosomes. GFP expression was detected in a wide range of murine tissues, including testis and the transgene was stably transmitted to a third generation of transgenic animals. This relatively simple, yet highly efficient, technique for generating transgenic animals by transducing spermatozoa with lentiviral vectors in vitro is a powerful tool for the study of fertilization/preimplantation development, vertical viral gene transmission, gene function and regulation, and epigenetic inheritance.

Polyomavirus middle T-antigen is a transmembrane protein that binds signaling proteins in discrete subcellular membrane sites.

Murine polyomavirus middle T-antigen (MT) induces tumors by mimicking an activated growth factor receptor. An essential component of this action is a 22-amino-acid hydrophobic region close to the C terminus which locates MT to cell membranes. Here, we demonstrate that this sequence is a transmembrane domain (TMD) by showing that a hemagglutinin (HA) tag added to the MT C terminus is exposed on the outside of the cells, with the N terminus inside. To determine whether this MT TMD is inserted into the endoplasmic reticulum (ER) membrane, we added the ER retention signal KDEL to the MT C terminus (MTKDEL). This mutant protein locates only in the ER, demonstrating that MT does insert into membranes solely at this location. In addition, this ER-located MT failed to transform. Examination of the binding proteins associated with the MTKDEL protein demonstrated that it associates with PP2A and c-Src but fails to interact with ShcA, phosphatidylinositol 3-kinase (PI3K), and phospholipase C-γ1 (PLC-γ1), despite being tyrosine phosphorylated. Additional mutant and antibody studies show that MT binding to PP2A is probably required for MT to efficiently exit the ER and migrate to the plasma membrane though the TMD also plays a role in this relocation. Overall, these data, together with previous publications, illustrate that MT associates with signaling proteins at different sites in its maturation pathway. MT binds to PP2A in the cytoplasm, to c-Src at the endoplasmic reticulum, and to ShcA, PI3K, and PLC-γ1 at subsequent locations en route to the plasma membrane.

Harnessing the tumour-derived cytokine, CSF-1, to co-stimulate T-cell growth and activation.

Aberrant growth factor production is a prevalent mechanism in tumourigenesis. If T-cells responded positively to a cancer-derived cytokine, this might result in selective enhancement of function within the tumour microenvironment. Here, we have chosen colony-stimulating factor-1 (CSF-1) as a candidate to test this concept. CSF-1 is greatly overproduced in many cancers but has no direct effects upon T-lymphocytes, which do not express the c-fms-encoded CSF-1 receptor. To confer CSF-1-responsiveness, we have expressed the human c-fms gene in immortalized and primary T-cells. Addition of soluble CSF-1 resulted in synergistic enhancement of IL-2-driven T-cell proliferation. CSF-1 also co-stimulated the production of interferon (IFN)-gamma by activated T-cells. These effects required Y809 of the CSF-1R and activation of the Ras-MEK-MAP kinase cascade, but were independent of PI3K signalling. T-cells that express c-fms are also responsive to membrane-anchored CSF-1 (mCSF-1) which, unlike its soluble counterpart, could co-stimulate IL-2 production. CSF-1 promoted chemotaxis of c-fms-expressing primary human T-cells and greatly augmented proliferation mediated by a tumour-targeted chimeric antigen receptor, with preservation of tumour cytolytic activity. Taken together, these data establish that T-cells may be genetically modified to acquire responsiveness to CSF-1 and provide proof-of-principle for a novel strategy to enhance the effectiveness of adoptive T-cell immunotherapy.

Exon junction sequences as cryptic splice sites: implications for intron origin.

Introns are flanked by a partially conserved coding sequence that forms the immediate exon junction sequence following intron removal from pre-mRNA. Phylogenetic evidence indicates that these sequences have been targeted by numerous intron insertions during evolution, but little is known about this process. Here, we test the prediction that exon junction sequences were functional splice sites that existed in the coding sequence of genes prior to the insertion of introns. To do this, we experimentally identified nine cryptic splice sites within the coding sequence of actin genes from humans, Arabidopsis, and Physarum by inactivating their normal intron splice sites. We found that seven of these cryptic splice sites correspond exactly to the positions of exon junctions in actin genes from other species. Because actin genes are highly conserved, we could conclude that at least seven actin introns are flanked by cryptic splice sites, and from the phylogenetic evidence, we could also conclude that actin introns were inserted into these cryptic splice sites during evolution. Furthermore, our results indicate that these insertion events were dependent upon the splicing machinery. Because most introns are flanked by similar sequences, our results are likely to be of general relevance.