PhiC31 integrase-mediated gene delivery has been extensively used in gene therapy and animal transgenesis. However, random integration events are observed in phiC31-mediated integration in different types of mammalian cells; as a result, the efficiencies of pseudo attP site integration and evaluation of site-specific integration are compromised. To improve this system, we used an attB-TK fusion gene as a negative selection marker, thereby eliminating random integration during phiC31-mediated transfection. We also excised the selection system and plasmid bacterial backbone by using two other site-specific recombinases, Cre and Dre. Thus, we generated clean transgenic bovine fetal fibroblast cells free of selectable marker and plasmid bacterial backbone. These clean cells were used as donor nuclei for somatic cell nuclear transfer (SCNT), indicating a similar developmental competence of SCNT embryos to that of non-transgenic cells. Therefore, the present gene delivery system facilitated the development of gene therapy and agricultural biotechnology.
The neurotrophin receptor p75(NTR) conveys multiple signals via its intracellular death domain. However, how the death domain is activated and interacts with downstream adaptors remains unclear. Here, we report two crystal structures of the p75(NTR) death domain in the form of a non-covalent asymmetric dimer and a Cys379-Cys379 disulfide bond linked symmetric dimer, respectively. These two dimer arrangements have not previously been observed in other death domain-containing proteins. Further analysis shows that both the Cys379-Cys379 disulfide linked and non-covalent full-length p75(NTR) dimers are present on the cell surface. These observations suggest that various oligomers may exist simultaneously on the cell surface, and that p75(NTR) activation and signalling may be modulated by neurotrophins or other factors via inducing a shift of the equilibrium between different oligomeric states.
NESCA, a newly discovered signaling adapter protein in the NGF-pathway, contains a RUN domain at its N-terminus. Here we report the crystal structure of the NESCA RUN domain determined at 2.0-Å resolution. The overall fold of the NESCA RUN domain comprises nine helices, resembling the RUN domain of RPIPx and the RUN1 domain of Rab6IP1. However, compared to the other RUN domains, the RUN domain of NESCA has significantly different surface electrostatic distributions at the putative GTPase-interacting interface. We demonstrate that the RUN domain of NESCA can bind H-Ras, a downstream signaling molecule of TrkA, with high affinity. Moreover, NESCA RUN can directly interact with TrkA. These results provide new insights into how NESCA participates in the NGF-TrkA signaling pathway.
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