Biology subjects

Schwab, J.

Publications and source records attributed to Schwab, J..

4 recordsLinked to original sources

bioRxiv2026

Notch-independent Her6 contributes to control of neural stem cell maintenance by shifting Notch signaling from lateral inhibition towards lateral induction mode

The growing brain faces the challenge to establish neural stem cell (NSC) populations that accomplish both stable NSC maintenance and dynamic generation of progenitors. Lineage-specific scRNA-seq and time series transcriptome analyses upon overexpression of Notch signaling components in the larval zebrafish brain reveal differential contributions of Notch signaling and Notch-independent Her6, a HES1 homolog, to NSC regulation. Notch signaling and Her6 distinctly regulate cell cycle genes to control G0/G1 or G2 exit and promote quiescence. Her6 and Notch activity combined differentially control delta, jagged, lfng and notch3 expression to potentially shift Notch signaling from Delta-driven lateral inhibition to Jagged-Notch3-mediated lateral induction. We propose that Her6 integrates cell-autonomous lineage-based information and lateral induction-mediated non-autonomous self-organization of neural proliferation zones. Her6-dependent lateral induction maintains persistent NSC patches in ventricular compartments with ongoing neurogenesis, and establishes coherent populations of long-term NSCs in active proliferation zones.

developmental biology↗

bioRxiv2025

The Inaugural Flatiron Institute Cryo-EM Conformational Heterogeneity Challenge

Despite the rise of single particle cryo-electron microscopy (cryo-EM) as a premier method for resolving macromolecular structures at atomic resolution, methods to address molecular heterogeneity in vitrified samples have yet to reach maturity. With an increasing number of new methods to analyze the multitude of heterogeneous states captured in single particle images, a systematic approach to validation in this field is needed. With this motivation, we issued a challenge to the community to analyze two cryo-EM particle image sets of thyroglobulin that exhibit continuous conformational heterogeneity. The first dataset was experimental and the second was generated with a simulator, allowing control over the distribution of molecular structures and enabled direct comparison between participants submissions and the ground truth molecular structures and distributions. Participants were asked to submit 80 volumes representing the heterogeneous ensemble and estimate their respective populations in the image sets provided. Participation of the research community in the challenge was strong, with submissions from nearly all developers of heterogeneity methods, resulting in 41 submissions across both datasets. Submissions qualitatively exceeded expectations, with the molecular motions identified by methods resembling both each other and the ground truth motion. However, quantitatively assessing these similarities was a challenge in and of itself. In the process of assessing the submissions, we developed several validation metrics, most of which require reference to the underlying ground truth volumes. However, we have also explored the use of metrics that do not necessarily reference ground truth. This is particularly apt for experimental datasets where ground truth is inaccessible. These approaches allowed us to assess the similarity and accuracy in volume quality, molecular motions, and conformational distribution of di!erent submissions. These metrics and the e!orts of all participants help chart a path forward for the improvements of heterogeneity methods for cryo-EM and for future challenges to validate these new methods as they continue to be developed by the community.

biophysics↗

bioRxiv2023

DynaMight: estimating molecular motions with improved reconstruction from cryo-EM images

How to deal with continuously flexing molecules is one of the biggest outstanding challenges in single-particle analysis of proteins from cryo-EM images. Here, we present DynaMight, a new software tool that estimates a continuous space of conformations in a cryo-EM data set by learning 3D deformations of a Gaussian pseudo-atomic model of a consensus structure for every particle image. Inversion of the learnt deformations is then used to obtain an improved reconstruction of the consensus structure. We illustrate the performance of DynaMight for several experimental cryo-EM data sets. We also show how error estimates on the deformations may be obtained by independently training two variational autoencoders (VAEs) on half sets of the cryo-EM data, and how regularisation of the 3D deformations through the use of atomic models may lead to important artefacts due to model bias. DynaMight is distributed as free, open-source software, as part of RELION-5.

biophysics↗

bioRxiv2022

Cryo-EM structure of the complete inner kinetochore of the budding yeast point centromere

SummaryThe point centromere of budding yeast specifies assembly of the large multi-subunit kinetochore complex. By direct attachment to the mitotic spindle, kinetochores couple the forces of microtubule dynamics to power chromatid segregation at mitosis. Kinetochores share a conserved architecture comprising the centromere-associated inner kinetochore CCAN (constitutive centromere-associated network) complex and the microtubule-binding outer kinetochore KMN network. The budding yeast inner kinetochore additionally includes the centromere-binding CBF1 and CBF3 complexes. Here, we reconstituted the complete yeast inner kinetochore complex assembled onto the centromere-specific CENP-A nucleosome (CENP-ANuc) and determined its structure using cryo-EM. This revealed a central CENP-ANuc, wrapped by only one turn of DNA, and harboring extensively unwrapped DNA ends. These free DNA duplexes function as binding sites for two CCAN protomers, one of which entraps DNA topologically and is positioned precisely on the centromere by the sequence-specific DNA-binding complex CBF1. The CCAN protomers are connected through CBF3 to form an arch-like configuration, binding 150 bp of DNA. We also define a structural model for a CENP-ANuc-pathway to the outer kinetochore involving only CENP-QU. This study presents a framework for understanding the basis of complete inner kinetochore assembly onto a point centromere, and how it organizes the outer kinetochore for robust chromosome attachment to the mitotic spindle.

biochemistry↗