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Dev Bio SuperGroup Meeting

Tuesday, May 13, 2014
12:00pm to 1:00pm
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Bacterial Phage Tail-like "Harpoons" Trigger Tubeworm Metamorphosis

 

­­­­Nicholas Shikuma, Newman lab

Free-swimming larvae of many bottom-dwelling marine organisms settle and metamorphose in response to environmentally specific physico-chemical cues. Bacteria resident in biofilms are often the source of these metamorphosis-inducing factors; however, the mechanisms that underpin this bacterium-mediated developmental transition were unknown. Larvae of the tubeworm Hydroides elegans, a significant biofouling agent, require direct contact with surface-bound bacteria to undergo metamorphosis and the bacterium Pseudoalteromonas luteoviolacea was shown to be a potent inducer of larval tubeworm metamorphosis. Through genetic and electron cryotomographic analyses, we show that arrays of Metamorphosis-Associated Contractile structures (MACs) produced by P. luteoviolacea trigger the metamorphosis of H. elegans. MACs are composed of about 100 contractile phage tail-like structures with outward-facing baseplates linked by tail fibers and a dynamic hexagonal lattice. Like phages, MAC arrays are synthesized intracellularly by P. luteoviolacea and are released by cell lysis. While P. luteoviolacea MACs benefit tubeworms by inducing metamorphosis, related phage tail-like structures in other bacteria are known to inject toxins into eukaryotes. This discovery expands the known diversity of structures and functions of phage-like particles and begins to explain how marine biofilms can trigger the metamorphosis of benthic animals.

 

 

Lattice light sheet imaging of live vertebrate embryos reveals novel processes during olfactory morphogenesis

 

Ankur Saxena, Bronner Lab

 The cranial ganglia and sense organs arise from two cell types: neural crest and ectodermal placodes. Both undergo cell migration and/or dynamic cell rearrangements. Most cranial peripheral neurons are derived from the placodes, with glia coming from the neural crest. In the olfactory system, the classical view has been that the olfactory placode forms all olfactory sensory neurons. In contrast, we recently showed that cranial neural crest cells are the primary source of microvillous sensory neurons in zebrafish (Saxena et al., 2013). Now, we expand upon those findings by utilizing the novel imaging technique lattice light sheet (LLS), a new derivative of Bessel plane SR-SIM (Gao et al., 2012). We have applied LLS to image zebrafish embryos for the first time and in doing so have revealed new details of olfactory organ formation at the highest spatiotemporal resolution to date in live vertebrates. Cell tracking analysis has produced a detailed timeline of olfactory organogenesis and traced the dual origins of migrating and differentiating neurons in real time.We have compiled both putatively stochastic and directed cell migration movements to build a four-dimensional 'blueprint' for assembly of a major sensory organ and created a new experimental system in which to study genetic perturbation at high-resolution in live vertebrates. In sum, LLS imaging allows us to answer cell migration/differentiation and cell-cell interaction questions that previously could not be addressed and to build a comprehensive developmental overview of the olfactory circuit and surrounding nasal cavity.


 

 

For more information, please contact Angela Stathopoulos by phone at x 5855 or by email at anglike@caltech.edu.