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This Week in PNAS: Nov 14, 2017

In the early, online version of the Proceedings of the National Academy of Sciences, researchers from Yale University explore effector proteins contributing to virulence in the organism behind Legionnaires' disease, Legionella pneumophila. Using a high-throughput transposon insertion sequencing strategy known as INSeq, the team screened for virulence-related effectors secreted by L. pneumophila in an infected mouse model or in cell culture, uncovering a bacteria protein that appeared to boost immune clearance and dampen L. pneumophila levels in the mouse lung. Other proteins identified by INSeq were implicated in L. pneumophila replication in mammalian cells or in the protozoa that can host the bug.

A team from Yale University and Temple University consider the possibility that body sizes in modern vertebrates resulted from evolutionary pulses instead of steady increments. The researchers established a maximum-likelihood framework to model pulsed and incremental evolution using available datasets representing body size data and other trait measurements for more than 8,300 dozens of vertebrate clades. "We found that a plurality of modern vertebrate clades examined are best fitted by pulsed processes over models of incremental change, stationary, and adaptive radiation," the authors say, noting that "our quantitative results are broadly compatible with both microevolutionary models and observations from the fossil record."

University of Rochester researchers report on results from a proteomic analysis aimed at tracking the trajectory of short-lived proteins and longer-lasting proteins during the shift from division and growth to quiescence in fibroblast cells. With the help of isotopic labeling, mass spectrometry, and protein-specific analyses such as Western blotting, the team saw signs that long-lived proteins are selectively degraded via lysosomal pathways and macroautophagy in fibroblasts that stop dividing. "Our results demonstrate that quiescent cells avoid the accumulation of long-lived proteins by enhancing their degradation through pathways involving the lysosome," they write. "This mechanism may be important for promotion of protein homeostasis in aged organisms."