Biology subjects

Nichols, E. L.

Publications and source records attributed to Nichols, E. L..

3 recordsLinked to original sources

bioRxiv2024

UNC-6/Netrin promotes both adhesion and directed growth within a single axon

During development axons undergo long-distance migrations as instructed by guidance molecules and their receptors, such as UNC-6/Netrin and UNC-40/DCC. Guidance cues act through long-range diffusive gradients (chemotaxis) or local adhesion (haptotaxis). However, how these discrete modes of action guide axons in vivo is poorly understood. Using time-lapse imaging of axon guidance in C. elegans, we demonstrate that UNC-6 and UNC-40 are required for local adhesion to an intermediate target and subsequent directional growth. Exogenous membrane-tethered UNC-6 is sufficient to mediate adhesion but not directional growth, demonstrating the separability of haptotaxis and chemotaxis. This conclusion is further supported by the endogenous UNC-6 distribution along the axons route. The intermediate and final targets are enriched in UNC-6 and separated by a ventrodorsal UNC-6 gradient. Continuous growth through the gradient requires UNC-40, which recruits UNC-6 to the growth cone tip. Overall, these data suggest that UNC-6 stimulates stepwise haptotaxis and chemotaxis in vivo.

developmental biology↗

bioRxiv2022

Structural insights into the formation of repulsive Netrin guidance complexes

Netrins can dictate attractive and repulsive responses during axon growth and cell migration, where presence of the receptor UNC-5 on target cells results in Netrin-mediated repulsion. Molecular details of Netrin-UNC-5 interactions and how they signal remain elusive. Here, we show that nematode UNC-5 is a heparin-binding protein, and the UNC-5-heparin affinity can be modulated using directed evolution or via rational design using our novel structure of UNC-5 with a heparin fragment. Furthermore, UNC-5 and nematode UNC-6/Netrin form a large, stable and rigid oligomeric complex in the presence of heparin, which can incorporate the attractive UNC-40/DCC receptor, demonstrating binary and ternary ectodomain complexes at preparative scale. C. elegans with a heparin-binding deficient UNC-5 fail to establish proper gonad morphology due to abrogated distal tip cell migration, which relies on repulsive UNC-5 signaling in response to UNC-6. Our findings establish Netrin responses to be mediated through glycosaminoglycan-regulated large macromolecular complexes.

biochemistry↗

bioRxiv2020

Instant FLIM enables 4D in vivo lifetime imaging of intact brains

Traditional fluorescence microscopy is blind to molecular microenvironment information that is present in fluorescence lifetime, which can be measured by fluorescence lifetime imaging microscopy (FLIM). However, existing FLIM techniques are typically slow to acquire and process lifetime images, difficult to implement, and expensive. Here, we present instant FLIM, an analog signal processing method that allows real-time streaming of fluorescence intensity, lifetime, and phasor imaging data through simultaneous image acquisition and instantaneous data processing. Instant FLIM can be easily implemented by upgrading an existing two-photon microscope using cost-effective components and our open-source software. We further improve the functionality, penetration depth, and resolution of instant FLIM using phasor segmentation, adaptive optics, and super-resolution techniques. We demonstrate through-skull intravital 3D FLIM of mouse brains to depths of 300 m and present the first in vivo 4D FLIM of microglial dynamics in intact and injured zebrafish and mouse brains up to 12 hours.

neuroscience↗