Exome sequencing reveals a <Emphasis Type="Italic">nebulin</Emphasis> nonsense mutation in a dog model of nemaline myopathy

Nemaline myopathy (NM) is a congenital muscle disorder associated with muscle weakness, hypotonia, and rod bodies in the skeletal muscle fibers. Mutations in 10 genes have been implicated in human NM, but spontaneous cases in dogs have not been genetically characterized. We identified a novel recessive myopathy in a family of line-bred American bulldogs (ABDs); rod bodies in muscle biopsies established this as NM. Using SNP profiles from the nuclear family, we evaluated inheritance patterns at candidate loci and prioritized TNNT1 and NEB for further investigation. Whole exome sequencing of the dam, two affected littermates, and an unaffected littermate revealed a nonsense mutation in NEB (g.52734272 C>A, S8042X). Whole tissue gel electrophoresis and western blots confirmed a lack of full-length NEB in affected tissues, suggesting nonsense-mediated decay. The pathogenic variant was absent from 120 dogs of 24 other breeds and 100 unrelated ABDs, suggesting that it occurred recently and may be private to the family. This study presents the first molecularly characterized large animal model of NM, which could provide new opportunities for therapeutic approaches.     

DNA binding studies of a new dicationic porphyrin. Insights into interligand interactions

Cationic porphyrins have an affinity for DNA and potential for applications in the fields of photodynamic therapy and cellular imaging. This report describes a new dicationic porphyrin, 5,15-dimethyl-10,20-di(N-methylpyridinium-4-yl)porphyrin, abbreviated H2tMe2D4. Although tetrasubstituted, H2tMe2D4 presents modest steric requirements and forms in reasonable yield by a "2+2" synthetic method. Accordingly, studies of the zinc(II)- and copper(II)-containing derivatives, Zn(tMe2D4) and Cu(tMe2D4), have also been possible. Methods used to characterize DNA-binding motifs include absorption, emission, linear, and circular dichroism spectroscopies, as well as viscometry. An unusually detailed picture of porphyrin uptake emerges. As the ratio of DNA to porphyrin increases during a typical titration, H2tMe2D4 or Cu(tMe2D4) initially aggregates on the host and then shifts to intercalative binding at close quarters before finally dispersing into non-interacting intercalation sites of the host. Emission studies of the copper(II) porphyrin have been very valuable. The existence of a measurable signal is diagnostic of intercalative binding, and the saturation behavior establishes that internalization typically monopolizes approximately three base pairs. In the moderate loading regime, emission data are most telling because dipole-dipole interactions between near-neighbor porphyrins tend to confuse other spectroscopic assays. The third ligand, Zn(tMe2D4), behaves differently in that the uptake is a strictly cooperative process. The mode of binding also varies with the base content of the DNA host. When the DNA is rich in A=T base pairs, the porphyrin remains five-coordinate and binds externally; however, Zn(tMe2D4) loses its axial ligand and binds by intercalation if the host contains only G[triple bond]C base pairs.     

Ontogeny and stability of separation and threat-induced defensive behaviors in rhesus monkeys during the first year of life

Twenty-six rhesus monkeys were tested repeatedly at 4, 8, and 12 months of age to characterize the expression and development of their defensive responses induced by separation from their mothers and exposure to a potential threat. Results demonstrated that by 4 months of age infant monkeys engaged in adult-like context-dependent responses and adaptively regulated these responses in relation to the changing context. When separated from their mothers and alone, infants at 4 months of age were active and emitted frequent coo vocalizations. However, when exposed to the profile of a human face, infants responded by becoming behaviorally inhibited and freezing. At 8 months of age, a dramatic reduction in infants' separation-induced coos was observed, whereas their duration of threat-induced freezing remained unchanged. At 12 months of age, a further decrease in cooing occurred, while freezing duration was maintained. No sex differences were found in the expression of these behaviors or their developmental patterns. Individual differences in separation-induced cooing and threat-induced freezing were apparent and remained stable over the three ages studied. However, within animals no relation was found between individual differences in cooing and freezing. These data demonstrate important differences in the developmental patterns for the expression of cooing and freezing over the first year of life. Marked individual differences in separation-induced cooing and threat-induced freezing were apparent and remained stable from 4–12 months of age. The data support the hypothesis that these different defensive responses reflect different adaptive responses that likely have different underlying mechanisms. The similarities between these defensive responses in rhesus monkeys and humans suggests that understanding the factors that promote the development of individual differences in monkeys will illuminate important factors that promote individual differences in humans. Am. J. Primatol. 44:125–135, 1998. ©1998 Wiley-Liss, Inc.     

Activation of cap-independent translation by variant eukaryotic initiation factor 4G in vivo

Protein synthesis is tightly controlled by assembly of an intricate ribonucleoprotein complex at the m⁷GTP-cap on eukaryotic mRNAs. Ensuing linear scanning of the 5′ untranslated region (UTR) is believed to transfer the preinitiation complex to the initiation codon. Eukaryotic mRNAs are characterized by significant 5′ UTR heterogeneity, raising the possibility of differential control of translation initiation rate at individual mRNAs. Curiously, many mRNAs with unconventional, highly structured 5′ UTRs encode proteins with central biological roles in growth control, metabolism, or stress response. The 5′ UTRs of such mRNAs may influence protein synthesis rate in multiple ways, but most significantly they have been implicated in mediating alternative means of translation initiation. Cap-independent initiation bypasses strict control over the formation of initiation intermediates at the m⁷GTP cap. However, the molecular mechanisms that favor alternative means of ribosome recruitment are not understood. Here we provide evidence that eukaryotic initiation factor (eIF) 4G controls cap-independent translation initiation at the c-myc and vascular endothelial growth factor (VEGF) 5′ UTRs in vivo. Cap-independent translation was investigated in tetracycline-inducible cell lines expressing either full-length eIF4G or a C-terminal fragment (Ct) lacking interaction with eIF4E and poly(A) binding protein. Expression of Ct, but not intact eIF4G, potently stimulated cap-independent initiation at the c-myc/VEGF 5′ UTRs. In vitro RNA-binding assays suggest that stimulation of cap-independent translation initiation by Ct is due to direct association with the c-myc/VEGF 5′ UTR, enabling 43S preinitiation complex recruitment. Our work demonstrates that variant translation initiation factors enable unconventional translation initiation at mRNA subsets with distinct structural features.     

An alginate hydrogel matrix for the localised delivery of a fibroblast/keratinocyte co-culture

There is significant interest in the development of tissue-engineered skin analogues, which replace both the dermal and the epidermal layer, without the use of animal or human derived products such as collagen or de-epidermalised dermis. In this study, we proposed that alginate hydrogel could be used to encapsulate fibroblasts and that keratinocytes could be cultured on the surface to form a bilayered structure, which could be used to deliver the co-culture to a wound bed, initially providing wound closure and eventually expediting the healing process. Encapsulation of fibroblasts in 2 and 5% w/v alginate hydrogel effectively inhibited their proliferation, whilst maintaining cell viability allowing keratinocytes to grow uninhibited by fibroblast overgrowth to produce a stratified epidermal layer. It was shown that the alginate degradation process was not influenced by the presence of fibroblasts within the hydrogel and that lowering the alginate concentration from 5 to 2% w/v increased the rate of degradation. Fibroblasts released from the scaffold were able to secrete extracellular matrix (ECM) and thus should replace the degrading scaffold with normal ECM following application to the wound site. These findings demonstrate that alginate hydrogel may be an effective delivery vehicle and scaffold for the healing of full-thickness skin wounds.     

Mutations in H5N1 Influenza Virus Hemagglutinin that Confer Binding to Human Tracheal Airway Epithelium

The emergence in 2009 of a swine-origin H1N1 influenza virus as the first pandemic of the 21st Century is a timely reminder of the international public health impact of influenza viruses, even those associated with mild disease. The widespread distribution of highly pathogenic H5N1 influenza virus in the avian population has spawned concern that it may give rise to a human influenza pandemic. The mortality rate associated with occasional human infection by H5N1 virus approximates 60%, suggesting that an H5N1 pandemic would be devastating to global health and economy. To date, the H5N1 virus has not acquired the propensity to transmit efficiently between humans. The reasons behind this are unclear, especially given the high mutation rate associated with influenza virus replication. Here we used a panel of recombinant H5 hemagglutinin (HA) variants to demonstrate the potential for H5 HA to bind human airway epithelium, the predominant target tissue for influenza virus infection and spread. While parental H5 HA exhibited limited binding to human tracheal epithelium, introduction of selected mutations converted the binding profile to that of a current human influenza strain HA. Strikingly, these amino-acid changes required multiple simultaneous mutations in the genomes of naturally occurring H5 isolates. Moreover, H5 HAs bearing intermediate sequences failed to bind airway tissues and likely represent mutations that are an evolutionary “dead end.” We conclude that, although genetic changes that adapt H5 to human airways can be demonstrated, they may not readily arise during natural virus replication. This genetic barrier limits the likelihood that current H5 viruses will originate a human pandemic.     

Identification of metabolites of the tryptase inhibitor CRA-9249: observation of a metabolite derived from an unexpected hydroxylation pathway

The metabolites of the tryptase inhibitor CRA-9249 were identified after exposure to liver microsomes. CRA-9249 was found to be degraded rapidly in liver microsomes from rabbit, dog, cynomolgus monkey, and human, and less rapidly in microsomes from rat. The key metabolites included cleavage of an aryl ether, in addition to an unexpected hydroxylation of the amide side chain adjacent to the amide nitrogen. The chemical structures of both metabolites were confirmed by synthesis and comparison to material isolated from the liver microsomes. Several suspected hydroxylated metabolites were also synthesized and analyzed as part of the structure identification process.