Type XV collagen occurs widely in the basement membrane zones of tissues, but its function is unknown. To understand the biological role of this protein, a null mutation in the Col15a1 gene was introduced into the germ line of mice. Despite the complete lack of type XV collagen, the mutant mice developed and reproduced normally, and they were indistinguishable from their wild-type littermates. However, Col15a1-deficient mice showed progressive histological changes characteristic for muscular diseases after 3 months of age, and they were more vulnerable than controls to exercise-induced muscle injury. Despite the antiangiogenic role of type XV collagen-derived endostatin, the development of the vasculature appeared normal in the null mice. Nevertheless, ultrastructural analyses revealed collapsed capillaries and endothelial cell degeneration in the heart and skeletal muscle. Furthermore, perfused hearts showed a diminished inotropic response, and exercise resulted in cardiac injury, changes that mimic early or mild heart disease. Thus, type XV collagen appears to function as a structural component needed to stabilize skeletal muscle cells and microvessels.T ype XV collagen belongs to the heterogeneous group of non-fibril-forming collagens and is thought to be a homotrimer consisting of three ␣1(XV) collagen chains (1). It is characterized by a central highly interrupted triple helical domain and large N-and C-terminal noncollagenous domains (2-4), and it has been shown to be a chondroitin sulfate proteoglycan (5). Type XV collagen mRNAs are expressed in many tissues, but the highest mRNA levels in the mouse can be detected in the heart and skeletal muscle (4). The protein is shown by immunostaining to have a widespread tissue distribution and has been localized mainly to the basement membrane zones, although it can also be found in the fibrillar collagen matrix of some tissues (6, 7). Its function is not known, however.In terms of primary structure, type XV collagen is highly homologous with type XVIII collagen, and together they form a distinct subgroup among the collagens (1, 3). They have thrombospondin-1 sequence homology in the N terminus, seven homologous collagenous domains, and highly homologous Cterminal noncollagenous domains. Type XVIII collagen is the precursor of endostatin, which has been shown to have a potent antiangiogenic effect (8), and the highest degree of homology between collagen types XV and XVIII involves the C-terminal endostatin sequence. The corresponding fragment in type XV collagen has also been shown to have antiangiogenic activity (9, 10).To understand the biological function and significance of type XV collagen, we generated a mouse strain lacking in ␣1(XV) collagen chains by site-specific Cre-loxP-mediated deletion in embryonic stem (ES) cells (11). The data suggest a structural role for type XV collagen in providing mechanical stability between cells and the extracellular matrix in skeletal muscle fibers and microvessels. Col15a1 deficiency leads to functional rather than struct...

Viral entry into host cells requires endocytosis machineries of the host for viral replication. PmRab7, a Penaeus monodon small GTPase protein, was investigated for its function in vesicular transport during viral infection. The double-stranded RNA of Rab7 was injected into a juvenile shrimp before challenging with white spot syndrome virus (WSSV) or yellow head virus (YHV). PmRab7 mRNA was specifically decreased at 48 h after dsRNA-Rab7 injection. Silencing of PmRab7 dramatically inhibited WSSV-VP28 mRNA and protein expression. Unexpectedly, the silencing of PmRab7 also inhibited YHV replication in the YHV-infected shrimp. These results suggested that PmRab7 is a common cellular factor required for WSSV or YHV replication in shrimp. Because PmRab7 should function in the endosomal trafficking pathway, its silencing prevents successful viral trafficking necessary for replication. Silencing of PmRab7 could be a novel approach to prevent both DNA virus (WSSV) and RNA virus (YHV) infection of shrimp.

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Taura syndrome virus (TSV) is a major cause of high mortality in Pacific white shrimp (Litopenaeus vannamei, Lv). Previously, silencing of Penaeus monodon Rab7 (PmRab7) by injecting double-stranded RNA corresponding to PmRab7 (dsRNA-PmRab7) prevented white spot syndrome virus or yellow head virus infection. Rab7 is proposed to be involved in intracellular trafficking of the viruses. This study aimed to investigate whether knockdown of Rab7 in L. vannamei by dsRNA-PmRab7 could inhibit replication of TSV. RNA interference (RNAi) technology using dsRNA targeting the LvRab7 gene was used to silence the mRNA expression of LvRab7. The silencing of the LvRab7 gene inhibited TSV replication dramatically when compared to groups receiving dsRNA-GFP or NaCl. This is the first demonstration that dsRNA targeting the endogenous shrimp gene LvRab7 strongly reduces TSV replication. It provides further evidence that LvRab7 is involved in the endosomal trafficking pathway of viruses infecting penaeid shrimp.

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