The Respiratory Syncytial Virus Phosphoprotein, Matrix Protein, and Fusion Protein Carboxy-Terminal Domain Drive Efficient Filamentous Virus-Like Particle Formation.

Virus-like particles (VLPs) are attractive as a vaccine concept. For human respiratory syncytial virus (hRSV), VLP assembly is poorly understood and appears inefficient. Hence, hRSV antigens are often incorporated into foreign VLP systems to generate anti-RSV vaccine candidates. To better understand the assembly, and ultimately to enable efficient production, of authentic hRSV VLPs, we examined the associated requirements and mechanisms. In a previous analysis in HEp-2 cells, the nucleoprotein (N), phosphoprotein (P), matrix protein (M), and fusion protein (F) were required for formation of filamentous VLPs, which, similar to those of wild-type virus, were associated with the cell surface. Using fluorescence and electron microscopy combined with immunogold labeling, we examined the surfaces of transfected HEp-2 cells and further dissected the process of filamentous VLP formation. Our results show that N is not required. Coexpression of P plus M plus F, but not P plus M, M plus F, or P plus F, induced both viral protein coalescence and formation of filamentous VLPs that resembled wild-type virions. Despite suboptimal coalescence in the absence of P, the M and F proteins, when coexpressed, formed cell surface-associated filaments with abnormal morphology, appearing longer and thinner than wild-type virions. For F, only the carboxy terminus (Fstem) was required, and addition of foreign protein sequences to Fstem allowed incorporation into VLPs. Together, the data show that P, M, and the F carboxy terminus are sufficient for robust viral protein coalescence and filamentous VLP formation and suggest that M-F interaction drives viral filament formation, with P acting as a type of cofactor facilitating the process and exerting control over particle morphology. IMPORTANCE: hRSV is responsible for >100,000 deaths in children worldwide, and a vaccine is not available. Among the potential anti-hRSV approaches are virus-like particle (VLP) vaccines, which, based on resemblance to virus or viral components, can induce protective immunity. For hRSV, few reports are available concerning authentic VLP production or testing, in large part because VLP production is inefficient and the mechanisms underlying particle assembly are poorly understood. Here, we took advantage of the cell-associated nature of RSV particles and used high-resolution microscopy analyses to examine the viral proteins required for formation of wild-type-virus-resembling VLPs, the contributions of these proteins to morphology, and the domains involved in incorporation of the antigenically important viral F protein. The results provide new insights that will facilitate future production of hRSV VLPs with defined shapes and compositions and may translate into improved manufacture of live-attenuated hRSV vaccines.

The respiratory syncytial virus fusion protein targets to the perimeter of inclusion bodies and facilitates filament formation by a cytoplasmic tail-dependent mechanism.

The human respiratory syncytial virus (HRSV) fusion (F) protein cytoplasmic tail (CT) and matrix (M) protein are key mediators of viral assembly, but the underlying mechanisms are poorly understood. A complementation assay was developed to systematically examine the role of the F protein CT in infectious virus production. The ability of F mutants with alanine substitutions in the CT to complement an F-null virus in generating infectious progeny was quantitated by flow cytometry. Two CT regions with impact on infectious progeny production were identified: residues 557 to 566 (CT-R1) and 569 to 572 (CT-R2). Substitutions in CT-R1 decreased infectivity by 40 to 85% and increased the level of F-induced cell-cell fusion but had little impact on assembly of viral surface filaments, which are believed to be virions. Substitutions in CT-R2, as well as deletion of the entire CT, abrogated infectious progeny production and impaired viral filament formation. However, CT-R2 mutations did not block but rather delayed the formation of viral filaments, which continued to form at a low rate and contained the viral M protein and nucleoprotein (N). Microscopy analysis revealed that substitutions in CT-R2 but not CT-R1 led to accumulation of M and F proteins within and at the perimeter of viral inclusion bodies (IBs), respectively. The accumulation of M and F at IBs and coincident strong decrease in filament formation and infectivity upon CT-R2 mutations suggest that F interaction with IBs is an important step in the virion assembly process and that CT residues 569 to 572 act to facilitate release of M-ribonucleoprotein complexes from IBs.

Interferon stimulated gene 15 (ISG15): molecular characterization and expression profile in endometrium of buffalo (Bubalus bubalis).

Interferon stimulated gene 15 (ISG15), one of the several proteins induced by conceptus derived Type I and/or a Type II interferon (IFN), is implicated as an important factor in determining the uterine receptivity and conceptus development. However, presence as well as specific role of the ISG15 in buffalo (Bubalus bubalis) reproduction is yet to be elucidated. In the present study, both genomic and cDNA sequences of bubaline (bu) ISG15 were cloned and investigated for its expression in different tissues of female reproductive tract of buffalo. Sequence analysis revealed 100% identity among the genomic sequences (1014 bp) of buISG15 from three different breeds of buffalo (viz., Murrah: Acc. No. DQ118137, Mehsana: Acc. No. DQ118138, and Nagpuri: Acc. No. DQ118136) and cDNAs (Acc. Nos. HM543268-HM543270). As in cattle, the buISG15 was comprised of two exons of 57 bp and 520 bp encoding a peptide of 154 amino acids. Moreover, the buISG15 cDNA sequence exhibited 98.3% and 98.5% identity with that of taurine and indicine cattle, respectively. Subsequent reverse transcription PCR analysis revealed expression of the buISG15 in the uterine endometrium, corpus luteum (CL), corpus hemorrhagicum and oviduct. Quantitative Real Time PCR (RTqPCR) analysis also confirmed the constitutive expression of the buISG15 in the uterine endometrium during different stages (i.e. estrus, diestrus and proestrus) of estrous cycle and also during early (∼d 30-40) pregnancy. Western blot analysis of the endometrial extract from both estrous cyclic as well as pregnant buffalo demonstrated the presence of only conjugated ISG15 which was >40 kDa. ISG15 mRNA and immune-reactive proteins were localized in the stromal as well as glandular epithelial cells of the uterine endometrium of estrous cyclic as well as pregnant buffalo. However, there was no significant difference in amount of ISG15 mRNA across the different reproductive phases. To conclude, this study will be helpful for the further understanding of the roles of the ISG15 in pregnancy of buffalo cows.

Primer extension-based method for the generation of a siRNA/miRNA expression vector.

RNA interference (RNAi) has become a powerful technique for studying gene function, biological pathways, and the physiology of diseases. Typically, the RNAi response in mammalian cells is mediated by small interfering RNA (siRNA). The use of synthesized siRNA to silence gene is relatively quick and easy, but it is costly with transient effects. A short hairpin RNA (shRNA) with complementary sense and antisense sequences of a target gene separated by a loop structure results in gene silencing that is as effective as chemically synthesized siRNA with fewer limitations. However, current methods for constructing shRNA vectors require the synthesis of long oligonucleotides, which is costly and often suffers from mutation problems during synthesis. Here, we report an alternative approach to generate a shRNA expression vector with high efficacy. We utilized shorter (