Summary In this report, we describe a novel method for producing mature and biologically active mono-biotinylated nerve growth factors (mBtNGF) that can be used for single molecule studies of real-time movement of neurotrophins within axons of neurons. We inserted an AviTag sequence into the C-terminal of the full length mouse preproNGF cDNA and cloned the fusion construct into a pcDNA3.1 mammalian expression vector. We also subcloned the E. coli biotin ligase, BirA, into a pcDNA3.1 vector. These two plasmids were then transiently co-expressed in HEK293FT cells. As a result, the AviTag located in the C-terminal of preproNGF was selectively ligated to a single biotin by BirA. The prepro sequence of NGF was subsequently cleaved within the cell. Mature mono-biotinylated NGF (mBtNGF) was secreted into cell culture media and was purified using Ni resin. We carried out activity assays and our results showed that mBtNGF retained biological activities that were comparable to normal NGF purified from mouse sub maxillary glands. We further verified the biotinylation efficiency of mBtNGF and the level of non-biotinylated NGF was virtually undetectable in the final preparation. Finally, by conjugating to quantum-dot streptavidin, mBtNGF was successfully used for single molecule study of axonal NGF trafficking in neurons.

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Background Internal medicine residents face numerous career options after residency training. Little is known about when residents make their final career choice. Objective We assessed the timing and predictive factors of final career choices among internal medicine residents at graduation, including demographics, pre-residency career preferences, and rotation scheduling. Methods We conducted a retrospective study of graduates of an academic internal medicine residency program from 2014 to 2017. Main measures included demographics, rotation schedules, and self-reported career choices for residents at 5 time points: recruitment day, immediately after Match Day, end of postgraduate year 1 (PGY-1), end of PGY-2, and at graduation. Results Of the 138 residents eligible for the study, 5 were excluded based on participation in a fast-track program for an Accreditation Council for Graduate Medical Education subspecialty fellowship. Among the remaining 133 residents, 48 (36%) pursued general internal medicine fields and 78 (59%) pursued fellowship training. Career choices from recruitment day, Match Day, and PGY-1 were only weakly predictive of the career choice. Many choices demonstrated low concordance throughout training, and general medicine fields (primary care, hospital medicine) were frequently not decided until after PGY-2. Early clinical exposure to subspecialty rotations did not predict final career choice. Conclusions Early career choices before and during residency training may have low predictability toward final career choices upon graduation in internal medicine. These choices may continue to have low predictability beyond PGY-2 for many specialties. Early clinical exposure may not predict final career choice for subspecialties.

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The study presents the removal of trace cadmium (II) in water with batch experiments by two kinds of manganese coagulants, HMO prepared from KMnO 4 and Na 2 S 2 O 3 , and HFMO prepared from KMnO 4 and FeSO 4 . Various parameters such as turbidity, pH, initial concentration of Cd(II) and coagulation time were investigated. The results showed that the cadmium can be better removed using HMO than by HFMO. With pH =6.72 and the Cd(II) initial concentration, 1mg/L, the dosage of HMO is 20mg/L, as the removal rate of cadmium is 85.04%. However, with pH = 8.03 and the Cd(II) initial concentration, 1mg/L, the dosage of HFMO is 20mg/L, as the removal rate of cadmium is 53.23%. The effectiveness of these two kinds of manganese coagulants for removal of cadmium and turbidity in natural water from Canal Jingmi in Beijing performed better when HMO is used than HFMO used. The paper indicated that HMO was an easily available and effective coagulant for the disposal of trace cadmium in water.

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