Search for: All records

ABSTRACT Biophysics research is exciting because physical approaches to biology can provide novel insights, and it is challenging because it requires knowledge and skills from multiple disciplines. We have developed an undergraduate biophysics laboratory module that teaches fundamental skills such as time-lapse microscopy, image analysis, programming, critical reading of scientific literature, and basics of scientific writing and peer review. The module is accessible to students who are familiar with introductory statistics, cell biology, and differential calculus. We used published research on the biomechanics ofHydramouth opening as a framework because it describes a stunning biological phenomenon:Hydra, a freshwater polyp, generates a multicell-wide mouth opening in an otherwise closed epithelium through extreme cell deformations within seconds. This publication was co–first authored by an undergraduate and was featured in the public press, thus providing multiple anchors that make the research accessible and motivating to undergraduates. Students start with a critical reading and discussion of the publication and then execute some of the experiments and analysis from the publication, thereby learning fluorescence time-lapse microscopy and image analysis by using ImageJ and/or MATLAB. Students quantify the kinematics of the tissue deformations during mouth opening and compare their data to the literature. The module culminates in the students writing a short paper about their results following themicroPublicationjournal style, a blinded peer review, and final paper submission. Here, we describe one possible implementation of the module with the necessary resources to reproduce it and summarize student feedback from a pilot run. We also provide suggestions for more advanced exercises and for using Python for data analysis. Several students expressed that repeating a published study completed by an undergraduate inspired and motivated them, thus creating buy-in and assurance that they can do it, which we expect to help with confidence and retention. 

Synopsis The freshwater cnidarian Hydra can regenerate from wounds, small tissue fragments and even from aggregated cells. This process requires the de novo development of a body axis and oral–aboral polarity, a fundamental developmental process that involves chemical patterning and mechanical shape changes. Gierer and Meinhardt recognized that Hydra’s simple body plan and amenability to in vivo experiments make it an experimentally and mathematically tractable model to study developmental patterning and symmetry breaking. They developed a reaction-diffusion model, involving a short-range activator and a long-range inhibitor, which successfully explained patterning in the adult animal. In 2011, HyWnt3 was identified as a candidate for the activator. However, despite the continued efforts of both physicists and biologists, the predicted inhibitor remains elusive. Furthermore, the Gierer-Meinhardt model cannot explain de novo axis formation in cellular aggregates that lack inherited tissue polarity. The aim of this review is to synthesize the current knowledge on Hydra symmetry breaking and patterning. We summarize the history of patterning studies and insights from recent biomechanical and molecular studies, and highlight the need for continued validation of theoretical assumptions and collaboration across disciplinary boundaries. We conclude by proposing new experiments to test current mechano-chemical coupling models and suggest ideas for expanding the Gierer-Meinhardt model to explain de novo patterning, as observed in Hydra aggregates. The availability of a fully sequenced genome, transgenic fluorescent reporter strains, and modern imaging techniques, that enable unprecedented observation of cellular events in vivo, promise to allow the community to crack Hydra’s secret to patterning. 

Hydrahas a tubular bilayered epithelial body column with a dome-shaped head on one end and a foot on the other.Hydralacks a permanent mouth: its head epithelium is sealed. Upon neuronal activation, a mouth opens at the apex of the head which can exceed the body column diameter in seconds, allowingHydrato ingest prey larger than itself. While the kinematics of mouth opening are well characterized, the underlying mechanism is unknown. We show thatHydramouth opening is generated by independent local contractions that require tissue-level coordination. We model the head epithelium as an active viscoelastic nonlinear spring network. The model reproduces the size, timescale and symmetry of mouth opening. It shows that radial contractions, travelling inwards from the outer boundary of the head, pull the mouth open. Nonlinear elasticity makes mouth opening larger and faster, contrary to expectations. The model correctly predicts changes in mouth shape in response to external forces. By generating innervated : nerve-free chimera in experiments and simulations, we show that nearest-neighbour mechanical signalling suffices to coordinate mouth opening.Hydramouth opening shows that in the absence of long-range chemical or neuronal signals, short-range mechanical coupling is sufficient to produce long-range order in tissue deformations.