Biology subjects

Rebay, I.

Publications and source records attributed to Rebay, I..

4 recordsLinked to original sources

bioRxiv2024

The Abelson kinase and the Nedd4-family E3 ligases co-regulate Notch trafficking to limit signaling

Precise output from the conserved Notch signaling pathway governs a plethora of cellular processes and developmental transitions. Unlike other pathways that use a cytoplasmic relay, the Notch cell surface receptor transduces signaling directly to the nucleus, with endocytic trafficking providing critical regulatory nodes. Here we report that the cytoplasmic tyrosine kinase Abelson (Abl) facilitates Notch internalization into late endosomes/multivesicular bodies (LEs), thereby limiting signaling output in both ligand-dependent and -independent contexts. Abl phosphorylates the PPxY motif within Notch, a molecular target for its degradation via Nedd4-family ubiquitin ligases. We show that Su(dx), a family member, mediates the Abl-directed LE regulation of Notch via the PPxY, while another family member, Nedd4Lo, contributes to Notch internalization into LEs through both PPxY-dependent and independent mechanisms. Our findings demonstrate how a network of post-translational modifiers converging at LEs cooperatively modulate Notch signaling to ensure the precision and robustness of its cellular and developmental functions.

developmental biology↗

bioRxiv2020

The Abelson tyrosine kinase and the Nedd4-family ubiquitin ligase Suppressor of Deltex converge at the Notch PPxY motif to regulate endosomal trafficking and signaling

The conserved Notch signaling pathway coordinates diverse cellular processes during animal development. Unlike most cell surface receptors that use a cytoplasmic cascade to amplify and diversify signaling dynamics, Notch itself transduces external cues directly to the nucleus. How appropriate signaling dynamics and transcriptional responses are achieved with this pathway architecture remains unclear. Here, we report that the cytoplasmic tyrosine kinase Abelson (Abl) fine-tunes Notch signaling by regulating Notch endocytic trafficking. We show that Abl can directly phosphorylate a PPxY motif important for Nedd4-family ubiquitin-ligase-mediated transfer of Notch into degradative endosomal compartments. Consistent with this, loss of Abl or inhibition of its kinase activity results in aberrant endosomal accumulation of Notch, while mutation of the PPxY tyrosine renders Notch insensitive to such regulation. Phenotypic and genetic interaction studies in the wing, together with parallel assays in cultured cells, show that loss or gain of Abl activity can respectively increase or decrease Notch output. We propose that the Notch PPxY motif operates as a molecular hub that integrates multiple post-translational modifications to regulate Notch trafficking and fine-tune signaling output.

developmental biology↗

bioRxiv2018

Ratio-based sensing of two transcription factors regulates the transit to differentiation

Cell state transitions are often triggered by large changes in the absolute concentrations of transcription factors and therefore large differences in the stoichiometric ratios between these factors. Whether cells can elicit state transitions using modest changes in the relative ratios of co-expressed factors is unclear. In this study we investigate how cells in the Drosophila eye resolve cell state transitions by quantifying the expression dynamics of the ETS transcription factors Pnt and Yan. We find that eye progenitor cells maintain a relatively constant ratio of Pnt/Yan protein despite expressing both proteins with pulsatile dynamics. A rapid and sustained two-fold increase in the Pnt/Yan ratio accompanies transitions to photoreceptor fates. Genetic perturbations that modestly disrupt the Pnt/Yan ratio produce fate transition defects consistent with the hypothesis that transitions are normally driven by a two-fold shift in the ratio. A biophysical model based on cooperative Yan-DNA binding coupled with non-cooperative Pnt-DNA binding illustrates how two-fold ratio changes could generate ultrasensitive changes in target gene transcription to drive fate transitions. In this way, coupling cell state transitions to the Pnt/Yan stoichiometric ratio sensitizes the system to modest fold-changes, conferring both robustness and ultrasensitivity to the developmental program.

developmental biology↗

bioRxiv2017

Cooperative recruitment of Yan to paired high affinity ETS sites organizes repression to confer specificity and robustness to cardiac cell fate specification

Cis regulatory elements (CREs) are defined by unique combinations of transcription factor binding sites. Emerging evidence suggests that the number, affinity and organization of sites play important roles in regulating enhancer output and ultimately gene expression. Here, we investigate how the cis-regulatory logic of a tissue-specific CRE responsible for even-skipped (eve) induction during cardiogenesis organizes the competing inputs of two ETS members, the activator Pointed (Pnt) and the repressor Yan. Using a combination of reporter gene assays and CRISPR-Cas9 gene editing, we show that Yan and Pnt have distinct preferences for affinity of sites. Not only does Yan prefer high affinity sites, but a tandem pair of such sites is necessary and sufficient for Yan to tune Eve expression levels in newly specified cardioblasts and to block ectopic Eve induction and cell fate specification in surrounding progenitors. Mechanistically, the cooperative Yan recruitment promoted by this conserved high affinity ETS pair not only biases Yan-Pnt competition at the specific CRE, but also organizes Yan repressive complexes in 3D across the eve locus. Taken together our results uncover a novel mechanism by which differential interpretation of CRE syntax by a competing repressor-activator pair can confer both specificity and robustness to developmental transitions.

developmental biology↗