Weiner, O. | Search bioRxiv

bioRxiv2018

Multiple sources of signal amplification within the B cell Ras/MAPK pathway

The Ras-Map kinase (MAPK) cascade underlies functional decisions in a wide range of cell types and organisms. In B cells, positive feedback-driven Ras activation is the proposed source of the digital (all-or-none) MAPK responses following antigen stimulation. However, an inability to measure endogenous Ras activity in living cells has hampered our ability to test this model directly. Here we leverage biosensors of endogenous Ras and ERK activity to revisit this question. We find that BCR ligation drives switch-like Ras activation and that lower BCR signaling output is required for the maintenance versus the initiation of Ras activation. Surprisingly, digital ERK responses persist in the absence of positive feedback-mediated Ras activation, and digital ERK is observed at a threshold level of Ras activation. These data suggest an independent analog-to-digital switch downstream of Ras activation, and reveals that multiple sources of signal amplification exist within the Ras-ERK module of the BCR pathway.

systems biology↗

bioRxiv2017

Chick cranial neural crest cells migrate by progressively refining the polarity of their protrusions.

In vivo quantitative imaging reveals that chick cranial neural crest cells throughout the migratory stream are morphologically polarized and migrate by progressively refining the polarity of their protrusions.\n\nAbstractTo move directionally, cells can bias the generation of protrusions or select among randomly generated protrusions. Here we use 3D two-photon imaging of chick branchial arch 2 directed neural crest cells to probe how these mechanisms contribute to directed movement, whether a subset or the majority of cells polarize during movement, and how the different classes of protrusions relate to one another. We find that cells throughout the stream are morphologically polarized along the direction of overall stream movement and that there is a progressive sharpening of the morphological polarity program. Neural crest cells have weak spatial biases in filopodia generation and lifetime. Local bursts of filopodial generation precede the generation of larger protrusions. These larger protrusions are more spatially biased than the filopodia, and the subset of protrusions that power motility are the most polarized of all. Orientation rather than position is the best correlate of the protrusions that are selected for cell movement. This progressive polarity refinement strategy may enable neural crest cells to efficiently explore their environment and migrate accurately in the face of noisy guidance cues.

developmental biology↗