The flow of genetic information in eukaryotic cells occurs through the nucleocytoplasmic translocation of mRNAs. Knowledge of in vivo messenger RNA export kinetics remains poor in comparison with that of protein transport. We have established a mammalian system that allowed the real-time visualization and quantification of large single mRNA-protein complexes (mRNPs) during export. The in vivo dynamics of bulk mRNP transport and export, from transcription to the nuclear pore complex (NPC), occurred within a 5-40 minute time frame, with no NPC pile-up. mRNP export was rapid (about 0.5 s) and kinetically faster than nucleoplasmic diffusion. Export inhibition demonstrated that mRNA-NPC interactions were independent of ongoing export. Nucleoplasmic transport dynamics of intron-containing and intronless mRNAs were similar, yet an intron did increase export efficiency. Here we provide visualization and analysis at the single mRNP level of the various steps in nuclear gene expression and the inter-chromatin tracks through which mRNPs diffuse, and demonstrate the kinetics of mRNP-NPC interactions and translocation.

Influenza A virus is a human pathogen whose genome is comprised of eight viral RNA segments that replicate in the nucleus. Two viral mRNAs are alternatively spliced. The unspliced M1 mRNA is translated into the matrix M1 protein while the ion channel M2 protein is generated after alternative splicing. These proteins are critical mediators of viral trafficking and budding. We show that influenza virus utilizes nuclear speckles to promote post-transcriptional splicing of its M1 mRNA. We assign previously unknown roles for the viral NS1 protein and cellular factors to an intranuclear trafficking pathway that targets the viral M1 mRNA to nuclear speckles, mediates splicing at these nuclear bodies, and exports the spliced M2 mRNA from the nucleus. Since nuclear speckles are storage sites for splicing factors, which leave these sites to splice cellular pre-mRNAs at transcribing genes, we reveal a functional subversion of nuclear speckles to promote viral gene expression.

SummaryNuclear transcribed genes produce mRNA transcripts destined to travel from the site of transcription to the cytoplasm for protein translation. Certain transcripts can be further localized to specific cytoplasmic regions. We examined the life cycle of a transcribed -actin mRNA throughout gene expression and localization, in a cell system that allows the in vivo detection of the gene locus, the transcribed mRNAs and the cytoplasmic -actin protein that integrates into the actin cytoskeleton. Quantification showed that RNA polymerase II elongation progressed at a rate of 3.3 kb/minute and that transactivator binding to the promoter was transient (40 seconds), and demonstrated the unique spatial structure of the coding and non-coding regions of the integrated gene within the transcription site. The rates of gene induction were measured during interphase and after mitosis, demonstrating that daughter cells were not synchronized in respect to transcription initiation of the studied gene. Comparison of the spatial and temporal kinetics of nucleoplasmic and cytoplasmic mRNA transport showed that the -actin-localization response initiates from the existing cytoplasmic mRNA pool and not from the newly synthesized transcripts arising after gene induction. It was also demonstrated that mechanisms of random movement were predominant in mediating the efficient translocation of mRNA in the eukaryotic cell.

Ovarian tissue auto-transplantation in post-pubertal women is capable of restoring fertility with over 80 live births currently reported with a corresponding pregnancy rate of 23 to 37%. The recently reported successes of live births from transplants, both in orthotopic and heterotopic locations, as well as the emerging methods of in vitro maturation (IVM), in vitro culture of primordial follicles, and possibility of in vitro activation (IVA) suggest new fertility options for many women and girls. Vitrification, as an ovarian tissue cryopreservation technique, has also demonstrated successful live births and may be a more cost-effective method to freezing with less tissue injury. Further, transplantation via the artificial ovary with an extracellular tissue matrix (ECTM) scaffolding as well as the effects of sphingosine-1-phosphate (SIP) and fibrin modified with heparin-binding peptide (HBP), heparin, and a vascular endothelial growth factor (VEGF) have demonstrated important advancements in fertility preservation. As a fertility preservation method, ovarian tissue cryopreservation and auto-transplantation are currently considered experimental, but future research may pave the way for these modalities to become a standard of care for women facing the prospect of sterility from ovarian damage.

In eukaryotic cells, the cytoplasm and the nucleus are separated by a double-membraned nuclear envelope (NE). Thus, transport of molecules between the nucleus and the cytoplasm occurs via gateways termed the nuclear pore complexes (NPCs), which are the largest intracellular channels in nature. While small molecules can passively translocate through the NPC, large molecules are actively imported into the nucleus by interacting with receptors that bind nuclear pore complex proteins (Nups). Regulatory factors then function in assembly and disassembly of transport complexes. Signaling pathways, cell cycle, pathogens, and other physiopathological conditions regulate various constituents of the nuclear transport machinery. Here, we will discuss several findings related to modulation of nuclear transport during physiological and pathological conditions, including tumorigenesis, viral infection, and congenital syndrome. We will also explore chemical biological approaches that are being used as probes to reveal new mechanisms that regulate nucleocytoplasmic trafficking and that are serving as starting points for drug development.