Hill, J. M. | bioRxiv Science

bioRxiv2021

Actin force generation in vesicle formation: mechanistic insights from cryo-electron tomography

Actin assembly provides force for a multitude of cellular processes. Compared to actin assembly- based force production during cell migration, relatively little is understood about how actin assembly generates pulling forces for vesicle formation. Here, cryo-electron tomography revealed actin filament number, organization, and orientation during clathrin-mediated endocytosis in human cells, showing that force generation is robust despite variance in network organization. Actin dynamics simulations incorporating a measured branch angle indicate that sufficient force to drive membrane internalization is generated through polymerization, and that assembly is triggered from [~]4 founding "mother" filaments, consistent with tomography data. Hip1R actin filament anchoring points are present along the entire endocytic invagination, where simulations show that it is key to pulling force generation, and along the neck, where it targets filament growth and makes internalization more robust. Actin cytoskeleton organization described here allowed direct translation of structure to mechanism with broad implications for other actin-driven processes. Highlights- Filament anchorage points are key to pulling force generation and efficiency. - Native state description of CME-associated actin force-producing networks. - Branched actin filament assembly is triggered from multiple mother filaments. - Actin force production is robust despite considerable network variability.

cell biology↗

bioRxiv2021

Accounting for point count ambient noise increases population size estimates

Ambient noise is an integral component of natural environments, but it also creates challenges for avian monitoring programs. Ambient noise can mask bird vocalizations from observers during point counts, which may lead to systematic undercounting of birds in noisy environments. Here, we estimate detection probability and population size in models that either account for or omit the influence of ambient noise. We used data for four bird species, from 2228 point counts that were conducted during the 2019 Mountain Birdwatch field season. Community scientists assessed ambient noise using a simple scale. Despite relatively quiet conditions at sampling locations (x = 2.48), our information theoretical approach favored N-mixture models that incorporated ambient noise into the detection function for all four species. At the noisiest sampling locations, our models predicted detection probabilities that were as low as 10% for some species. Accounting for ambient noise resulted in a modest, mean increase of [≤]3.29% in the total population size for each species. Following our approach, other researchers can easily incorporate ambient noise assessments into their field protocols and analyses, with minimal costs or added complexity, to increase the comparability of studies conducted within different acoustic environments.

ecology↗