“Single-molecule visualization of a formin-capping protein ‘decision complex’ at the actin filament barbed end”
Regulation of actin filament length is a central process by which eukaryotic cells control the shape, architecture, and dynamics of their actin networks. This regulation plays a fundamental role in cell motility, morphogenesis, and a host of processes specific to particular cell types. This paper by recently graduated [Biophysics and Structural Biology] Ph.D. student Jeffrey Bombardier and collaborators resolves the long-standing mystery of how formins and capping protein work in concert and antagonistically to control actin filament length. Bombardier used the CoSMoS multi-wavelength single-molecule fluorescence microscopy technique to to discover and characterize a novel tripartite complex formed by a formin, capping protein, and the actin filament barbed end. Quantitative analysis of the kinetic mechanism showed that this complex is the essential intermediate and decision point in converting a growing formin-bound filament into a static capping protein-bound filament, and the reverse. Interestingly, the authors show that “mDia1 displaced from the barbed end by CP can randomly slide along the filament and later return to the barbed end to re-form the complex.” The results define the essential features of the molecular mechanism of filament length regulation by formin and capping protein; this mechanism predicts several new ways by which cells are likely to couple upstream regulatory inputs to filament length control.Single-molecule visualization of a formin-capping protein ‘decision complex’ at the actin filament barbed end
Jeffrey P. Bombardier, Julian A. Eskin, Richa Jaiswal, Ivan R. Corrêa, Jr., Ming-Qun Xu, Bruce L. Goode, and Jeff Gelles
Nature Communications 6:8707 (2015)
The capping protein expression plasmid described in this article is available from Addgene.
Readers interested in this subject should also see a related article by Shekhar et al published simultaneously in the same journal. We are grateful to the authors of that article for coordinating submission so that the two articles were published together.
Life is tough. Every living thing is constantly dealing with insults that damage or disrupt homeostasis. At the cellular level these insults, or stresses, come in multiple forms: starvation, oxidative stress, heat shock, radiation damage, and infection. In response to these stresses, organisms have evolved numerous mechanisms to promote survival. Broadly speaking, an insult stimulates various signaling cascades that alter gene expression in the cell.
One way this is achieved is through the “turning on” of transcription factors. One such transcription factor is FOXO, which is activated under many types of stress, both metabolic and environmental. Another way gene expression can be accomplished is the post-transcriptional control of gene expression. An important player of post-transcriptional control is the small RNA pathways composed of the RNA interference (RNAi), micro RNA (miRNA), and PIWI RNA (piRNA) branches. In a recent article from the Marr lab titled “FOXO regulates RNA interference in Drosophila and protects from RNA virus infection”, published in PNAS this November, the authors identify a new connection between both the transcriptional and small RNA mediated post-transcriptional mechanisms that respond to stress.
Using Drosophila as a model system, the authors identify FOXO as a transcription factor that regulates important genes in the small RNA pathways in response to stress. This is the first transcription factor identified to control these genes. Despite being a hot and competitive field for over 15 years, work in small RNA pathways had yet to reveal the transcriptional regulation of the core protein machinery that are involved in small RNA biogenesis and utilization. Under stress conditions, FOXO directly binds the promoters of core small RNA pathway genes, such as Ago1, Ago2, and Dicer 2, leading to increases in their expression. As one might expect, this is followed by an increase in RNAi efficiency and post-transcriptional control of gene expression.
A known physiological role for RNAi is to fight off viral infections as part of an innate immune response. The authors find that FOXO is activated by viral infection to promote this anti-viral response. In addition, animals deleted for the FOXO gene are more susceptible to a viral infection. Theses results are consistent with the notion that virally-activated FOXO stimulates RNAi gene transcription as a mechanism to enhance viral immunity.
Finally, the work in this paper identifies integration between metabolic and stress signaling and the innate immune response, with FOXO serving the bridge. There is evidence that acute stress can confer a protective effect against infection in humans. If the identified role of FOXO is conserved, perhaps it can be utilized therapeutically.
Spellberg MJ, Marr MT, 2nd. FOXO regulates RNA interference in Drosophila and protects from RNA virus infection. Proc Natl Acad Sci U S A. 2015
We noticed a new paper this week in Brain Research on chronic traumatic encephalopathy (brain damage from repeated blows to the head, which has been all over the news this year) from a Brandeis author, Madeline Engeler ’16, a Biology/HSSP double major.
We reached out to Madeline for the inside scoop, here’s what she told us:
Yes this is my paper. I am so excited it is finally published! […] This research came from the summer of 2014 when I was at the Cleveland Clinic Lerner Research Institute. I was funded through Brandeis’ World of Work fellowship program and I gained credit for my HSSP hands-on experience.This research came about from some of us in the lab reading papers about post-mortem diagnosis of CTE in NFL players. What was intriguing was that very similar morphologies were seen in the epileptic brain resections we were studying. So we decided to depart from our epileptic brain research and stained these samples with the same antibodies as in the CTE papers. We also obtained NFL brain samples from Dr. Mckee at BU to do our own staining. Our results showed remarkably similar images from the epileptic and CTE brains. This caused us to posit that perhaps the post-mortem diagnosis of CTE is too broad because it encompasses other neurological conditions, such as epilepsy.
You can read the paper for yourself online:
Puvenna V, Engeler M, Banjara M, Brennan C, Schreiber P, Dadas A, Bahrami A, Solanki J, Bandyopadhyay A, Morris JK, Bernick C, Ghosh C, Bazarian JJ, Janigro D. Is phosphorylated tau unique to chronic traumatic encephalopathy? Phosphorylated tau in epileptic brain and chronic traumatic encephalopathy. Brain Res. 2015.
We’re constantly bombarded by advice on which foods to eat or not eat, but skeptics among us often find compelling evidence for a convincing mechanism of how the foods promote health hard to come by – food has many components, and there are many different cells and metabolic pathways in those cells with which those components interact.
Consider broccoli. It is well established that cruciferous vegetables have wide-ranging health benefits, apparently reducing cancer risks and lowering inflammation. One set of phytochemicals responsible for the potent anti-cancer and anti-inflammatory properties are called isothiocyanates or ‘ITCs’. It is now four decades since the discovery of ITCs, yet a molecular understanding of what ITCs do in a cell has proven elusive.
In a paper published this month in Cancer Research, Brandeis research scientist Ann Lawson, working in Liz Hedstrom’s laboratory, together with graduate students Marcus Long (Biochem) and Rory Coffey (Mol Cell Biol) and scientists from UbiQ and from Boston College, has shown that ITCs block the action of deubiquitinating enzymes (DUBs), including the tumorigenesis-associated enzymes USP9x and UCH37, at physiologically relevant concentrations and time scales.
DUB inhibition provides a simple, unifying explanation that can account for many of the diverse health effects of ITCs. Understanding of how ITCs work at the molecular level may, one day, lead to new drug therapies for illnesses such as cancer, chronic inflammation, and neurodegenerative diseases.
Hampton University and Brandeis University have formed a new initiative called the Partnership for Research and Education in Materials (PREM). Using a 5-year, $3 million grant from the National Science Foundation, the two universities have joined forces to foster interest in research science in under-represented groups of undergraduates.
A joint Pathway to Professorship (PtP) program will offer a path for under-represented research assistant professors to advance their research and possibly reach a tenure-track professorship at Brandeis or Hampton. These unique training positions could be filled by applicants in most disciplines including Biology, Chemistry, Physics, and Engineering. They involve one-year residences at Brandeis and Hampton Universities. Recruiting has started – interested applicants should start at the Hampton Career Opportunities website.
- see also BrandeisNow.
Professor of Biology Piali Sengupta gave the 2015 Stetten Lecture at NIGMS on Oct 21 on Form Meets Function: Structurally Diverse Cilia and Their Roles in Sensory Signaling. The “cilia squad” in the Sengupta Lab has been working for some years now to examine cilia formation in sensory neurons in the nematode C. elegans, and the relationship between the structure and nerve cell function. You can watch Piali’s lecture online.
Gio Bosco is a die-hard chromatin regulation guy who became interested in whether long-term changes in DNA structure are involved in long-term behavioral plasticity. Gio did his PhD work in Jim Haber’s lab and provided some of the earliest and strongest evidence for a critical DNA repair mechanism called break-induced replication, which plays an essential role in maintaining the integrity of chromosome ends when the normal end-addition of DNA by telomerase is absent.
In his postdoctoral work, Giovanni turned from using yeast as a model system to Drosophila. In the lab of Terry Orr-Weaver at MIT he focused his attention on the role of DNA replication in regulating gene amplifications and became interested in the importance of post-translational modifications (acetylations and phosphorylations) of the histone proteins that wrap the DNA into chromatin.
Approximately 7 years ago Gio started contemplating the question of how these post-translational histone modifications change during behavior and learning. He returned to his Brandeis roots to develop tools and approaches to address this problem. He received an NIH K18 grant to fund a sabbatical in Leslie Griffith’s lab in 2010. He and his behavior group have remained connected to Brandeis since then through frequent joint group meeting visits.
We’ll be interested to hear more about the role of histone modifications in how learning and memory occurs in the context of social behavior, and in how social behavior can be inherited through multiple generations, as the result of the Bosco lab research funded by this award.