Chugh, M. | Search bioRxiv

bioRxiv2025

U.S. Visa Bureaucracy and Its Burdens Among Early Career Scholars

Foreign-born research scholars on temporary visas are essential to the U.S. scientific workforce and economy, yet they face systemic challenges shaped by restrictive immigration policies. While scholars across disciplines have long analyzed the evolution of U.S. immigration regimes and citizenship privilege, there remains a critical lack of quantitative data on the financial, temporal, and psychological burdens associated with visa bureaucracy. Here we present original survey data from more than 700 international postdoctoral researchers at Harvard Medical School (HMS) and its affiliated institutions, revealing how visa-related burdens directly impact scholars and their research. For example, over 40% of scholars reported spending more than a month in their home countries to renew U.S. visas, with 5% spending more than six months. Scholars from Asia experienced longer delays and higher costs than those from Europe. Seventy-five percent of respondents reported mental health challenges related to visa stress, often feeling trapped at work, with some requiring medication and time off. Our findings underscore the urgent need for targeted institutional support to promote research productivity, equitable opportunity, and mental well-being. As the U.S. repositions itself as a global scientific leader, such reforms will be critical to recruiting and retaining top talent and advancing equity in science.

scientific communication and education↗

bioRxiv2019

The kinesin-8 Kip3 depolymerizes microtubules with a collective force-dependent mechanism

Microtubules are highly dynamic filaments with dramatic structural rearrangements and length changes during the cell cycle. An accurate control of the microtubule length is essential for many cellular processes in particular, during cell division. Motor proteins from the kinesin-8 family depolymerize microtubules by interacting with their ends in a collective and length-dependent manner. However, it is still unclear how kinesin-8 depolymerizes microtubules. Here, we tracked the microtubule end-binding activity of yeast kinesin-8, Kip3, under varying loads and nucleotide conditions using high-precision optical tweezers. We found that single Kip3 motors spent up to 200 s at the microtubule end and were not stationary there but took several 8-nm forward and backward steps that were suppressed by loads. Interestingly, increased loads, similar to increased motor concentrations, also exponentially decreased the motors residence time at the microtubule end. On the microtubule lattice, loads also exponentially decreased the run length and time. However, for the same load, lattice run times were significantly longer compared to end residence times suggesting the presence of a distinct force-dependent detachment mechanism at the microtubule end. The force dependence of the end residence time enabled us to estimate what force must act on a single motor to achieve the microtubule depolymerization speed of a motor ensemble. This force is higher than the stall force of a single Kip3 motor, supporting a collective force-dependent depolymerization mechanism that unifies the so-called "bump-off" and "switching" models. Understanding the mechanics of kinesin-8s microtubule end activity will provide important insights into cell division with implications for cancer research. STATEMENT OF SIGNIFICANCEKinesin-8 motors are important for microtubule length regulation and are over-expressed in different types of cancer. Yet, on the molecular level, it is unclear how these motors depolymerize microtubules. Using high-precision optical tweezers, we measured how single yeast kinesin-8 motors, Kip3, interacted with the microtubule end. Interestingly, we found that single Kip3 motors were still motile at the microtubule end. The force dependence of how long single motors were associated with the microtubule end enabled us to estimate what force motors must exert onto each other to achieve the collective microtubule depolymerization speed of many motors. Our data support a collective force-dependent depolymerization mechanism. A better understanding of Kip3s microtubule end activity has implications for cell division and associated diseases.

biophysics↗