Research has previously shown that, without methionine supplements, neural tube proteins of rat embryos cultured on bovine sera were hypomethylated and neural tubes failed to close. In the present study, to identify the proteins that became methylated during neurulation, rat embryos were first cultured on methionine-deficient bovine serum for 40 hr, then incubated with puromycin for 1 hr, and, finally, incubated with [methyl-14 C]methionine and puromycin for 5 hr. On the basis of molecular weights, isoelectric points, and Western immunoblots, the methyl-14 C-labeled proteins were identified as actin, ␣␤-tubulin, and neurofilament L. Indirect immunof luorescence studies indicated that without the addition of methionine to the culture, localization of actin and ␣␤-tubulin in the basal cytoplasm did not occur and these neuroepithelial cells lost their columnar morphology.

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The SARS-CoV-2 global pandemic has produced widespread shortages of certified air-filtering personal protection equipment and an acute need for rapid evaluation of breathability and filtration efficiency of proposed alternative solutions. Here, we describe experimental efforts to nondestructively quantify three vital characteristics of mask approaches: breathability, material filtration effectiveness, and sensitivity to fit. We focus on protection against aqueous aerosols >0.3 μm using off-the-shelf particle, flow, and pressure sensors, permitting rapid comparative evaluation of these three properties. We present and discuss both the pressure drop and the particle penetration as a function of flow to permit comparison of relative protection for a set of proposed filter and mask designs. The design considerations of the testing apparatus can be reproduced by university laboratories and medical facilities and used for rapid local quality control of respirator masks that are of uncertified origin, monitoring the long-term effects of various disinfection schemes and evaluating improvised products not designed or marketed for filtration.