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Haesemeyer M.,Harvard University | Robson D.N.,Harvard University | Robson D.N.,The Rowland Institute at Harvard | Li J.M.,Harvard University | And 5 more authors.
Cell Systems | Year: 2015

Avoiding temperatures outside the physiological range is critical for animal survival, but how temperature dynamics are transformed into behavioral output is largely not understood. Here, we used an infrared laser to challenge freely swimming larval zebrafish with “white noise” heat stimuli and built quantitative models relating external sensory information and internal state to behavioral output. These models revealed that larval zebrafish integrate temperature information over a time-window of 400 ms preceding a swim bout and that swimming is suppressed right after the end of a bout. Our results suggest that larval zebrafish compute both an integral and a derivative across heat in time to guide their next movement. Our models put important constraints on the type of computations that occur in the nervous system and reveal principles of how somatosensory temperature information is processed to guide behavioral decisions such as sensitivity to both absolute levels and changes in stimulation. © 2015 Elsevier Inc.


Spicer R.,The Rowland Institute at Harvard | Groover A.,U.S. Department of Agriculture
New Phytologist | Year: 2010

Secondary growth from vascular cambia results in radial, woody growth of stems. The innovation of secondary vascular development during plant evolution allowed the production of novel plant forms ranging from massive forest trees to flexible, woody lianas. We present examples of the extensive phylogenetic variation in secondary vascular growth and discuss current knowledge of genes that regulate the development of vascular cambia and woody tissues. From these foundations, we propose strategies for genomics-based research in the evolution of development, which is a next logical step in the study of secondary growth. No claim to original US government works. Journal compilation © New Phytologist Trust (2010).


Orth A.,The Rowland Institute at Harvard | Orth A.,RMIT University | Tomaszewski M.J.,Thermo Fisher Scientific | Ghosh R.N.,Thermo Fisher Scientific | Schonbrun E.,The Rowland Institute at Harvard
Optica | Year: 2015

Understanding the complexity of cellular biology often requires capturing and processing an enormous amount of data. In high-content drug screens, each cell is labeled with several different fluorescent markers and frequently thousands to millions of cells need to be analyzed in order to characterize biology’s intrinsic variability. In this work, we demonstrate a new microlens-based multispectral microscope designed to meet this throughput-intensive demand. We report multispectral image cubes of up to 1.30 gigapixels in the spatial domain, with up to 13 spectral samples per pixel, for a total image size of 16.8 billion spatial–spectral samples. To our knowledge, this is the largest multispectral microscopy dataset reported in the literature. Our system has highly reconfigurable spectral sampling and bandwidth settings, and we have demonstrated spectral unmixing of up to six fluorescent channels. This technology has the potential to speed up drug discovery by alleviating the imaging bottleneck in image-based assays. © 2015 Optical Society of America.


PubMed | Anhui University of Science and Technology and The Rowland Institute at Harvard
Type: Journal Article | Journal: Journal of the Royal Society, Interface | Year: 2014

Swimming bacteria explore their environment by performing a random walk, which is biased in response to, for example, chemical stimuli, resulting in a collective drift of bacterial populations towards a better life. This phenomenon, called chemotaxis, is one of the best known forms of collective behaviour in bacteria, crucial for bacterial survival and virulence. Both single-cell and macroscopic assays have investigated bacterial behaviours. However, theories that relate the two scales have previously been difficult to test directly. We present an image analysis method, inspired by light scattering, which measures the average collective motion of thousands of bacteria simultaneously. Using this method, a time-varying collective drift as small as 50 nm s(-1) can be measured. The method, validated using simulations, was applied to chemotactic Escherichia coli bacteria in linear gradients of the attractant -methylaspartate. This enabled us to test a coarse-grained minimal model of chemotaxis. Our results clearly map the onset of receptor methylation, and the transition from linear to logarithmic sensing in the bacterial response to an external chemoeffector. Our method is broadly applicable to problems involving the measurement of collective drift with high time resolution, such as cell migration and fluid flows measurements, and enables fast screening of tactic behaviours.


PubMed | The Rowland Institute at Harvard and Harvard University
Type: Journal Article | Journal: Physical review. E | Year: 2016

We present a mathematical model for Joule heating of an electrolytic solution in a nanopore. The model couples the electrical and thermal dynamics responsible for rapid and extreme superheating of the electrolyte within the nanopore. The model is implemented numerically with a finite element calculation, yielding a time and spatially resolved temperature distribution in the nanopore region. Temperatures near the thermodynamic limit of superheat are predicted to be attained just before the explosive nucleation of a vapor bubble is observed experimentally. Knowledge of this temperature distribution enables the evaluation of related phenomena including bubble nucleation kinetics, relaxation oscillation, and bubble dynamics.


PubMed | The Rowland Institute at Harvard
Type: Journal Article | Journal: Proceedings of the National Academy of Sciences of the United States of America | Year: 2013

Axonemes form the core of eukaryotic flagella and cilia, performing tasks ranging from transporting fluid in developing embryos to the propulsion of sperm. Despite their abundance across the eukaryotic domain, the mechanisms that regulate the beating action of axonemes remain unknown. The flagellar waveforms are 3D in general, but current understanding of how axoneme components interact stems from 2D data; comprehensive measurements of flagellar shape are beyond conventional microscopy. Moreover, current flagellar model systems (e.g., sea urchin, human sperm) contain accessory structures that impose mechanical constraints on movement, obscuring the native axoneme behavior. We address both problems by developing a high-speed holographic imaging scheme and applying it to the (male) microgametes of malaria (Plasmodium) parasites. These isolated flagella are a unique, mathematically tractable model system for the physics of microswimmers. We reveal the 3D flagellar waveforms of these microorganisms and map the differential shear between microtubules in their axonemes. Furthermore, we overturn claims that chirality in the structure of the axoneme governs the beat pattern [Hirokawa N, et al. (2009) Ann Rev Fluid Mech 41:53-72], because microgametes display a left- or right-handed character on alternate beats. This breaks the link between structural chirality in the axoneme and larger scale symmetry breaking (e.g., in developing embryos), leading us to conclude that accessory structures play a critical role in shaping the flagellar beat.


PubMed | The Rowland Institute at Harvard
Type: Journal Article | Journal: The New phytologist | Year: 2010

Secondary growth from vascular cambia results in radial, woody growth of stems. The innovation of secondary vascular development during plant evolution allowed the production of novel plant forms ranging from massive forest trees to flexible, woody lianas. We present examples of the extensive phylogenetic variation in secondary vascular growth and discuss current knowledge of genes that regulate the development of vascular cambia and woody tissues. From these foundations, we propose strategies for genomics-based research in the evolution of development, which is a next logical step in the study of secondary growth.

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