Biology subjects

Spitz, D.

Publications and source records attributed to Spitz, D..

5 recordsLinked to original sources

bioRxiv2026

Parameters for stable Notch-independent Her6 oscillations across a frequency spectrum in neural stem cell populations

Neural proliferation zones drive the major growth phases of the vertebrate brain. Notch signaling and HES/Her transcription factors control neural stem cell (NSC) maintenance and neurogenesis, however the dynamic regulation of neural proliferation zones to sustain growth is not well understood. Notch-independent expression of the zebrafish HES1 homolog her6 in the larval brain is required for NSC maintenance and growth. We generated an mNeonGreen knock-in into the her6 locus and quantified Her6-mNeonGreen oscillations in vivo in distinct NSC populations. Her6 oscillates cell-autonomously across a broader frequency range, unaffected by inhibition of Notch signaling, and robustly reinitiated after experimental perturbations. Mathematical modelling reveals that Her6 oscillations prevail only when both transcript and protein degradation rate constants are equal. These intrinsic control parameters may have evolved to enable the Her6 oscillator to robustly maintain stemness during proliferative phases irrespective of local Notch signaling cues, and to provide for lineage stability while retaining plasticity for lineage progression.

developmental biology↗

bioRxiv2024

ComboPath: An ML system for predicting drug combination effects with superior model specification

Drug combinations have been shown to be an effective strategy for cancer therapy, but identifying beneficial combinations through experiments is labor-intensive and expensive [Mokhtari et al., 2017]. Machine learning (ML) systems that can propose novel and effective drug combinations have the potential to dramatically improve the efficiency of combinatoric drug design. However, the biophysical parameters of drug combinations are degenerate, making it difficult to identify the ground truth of drug interactions even given experimental data of the highest quality available. Existing ML models are highly underspecified to meet this challenge, leaving them vulnerable to producing parameters that are not biophysically realistic and harming generalization. We have developed a new ML model, "ComboPath", aimed at a novel ML task: to predict interpretable cellular dose response surface of a two-drug combination based on each drugs interactions with their known protein targets. ComboPath incorporates a biophysically-motivated intermediate parameterization with prior information used to improve model specification. This is the first ML model to nominate beneficial drug combinations while simultaneously reconstructing the dose response surface, providing insight on both the potential of a drug combination and its optimal dosing for therapeutic development. We show that our models were able to accurately reconstruct 2D dose response surfaces across held out combination samples from the largest available combinatoric screening dataset while substantially improving model specification for key biophysical parameters.

biophysics↗

bioRxiv2022

A network of Notch-dependent and -independent her genes controls neural stem and progenitor cells in the zebrafish thalamic proliferation zone

Neural proliferation zones mediate brain growth, and employ Delta/Notch signaling and HES/HER transcription factors to balance neural stem cell (NSC) maintenance and generation of progenitors and neurons. We investigated Notch-dependency and function of her genes in the thalamic proliferation zone of developing zebrafish larvae. Nine Notch-dependent genes, her2, her4.1-5, her12, her15.1-2, and two Notch-independent genes, her6, her9, are differentially expressed, and define distinct NSC and progenitor populations. her6 prominently executes patterning information to maintain NSCs and the zona limitans intrathalamica Shh signaling activity. her6, her9 double mutants reveal that Notch-independent her genes predominantly regulate NSC maintenance and transition into the progenitor pool. Surprisingly, combined deletion of all Notch-dependent her genes does not affect NSCs or progenitor formation. Combined genetic manipulation of up to eleven Notch-dependent and -independent her genes revealed that Notch-dependent her genes may regulate progenitor progression into neurogenesis, but not progenitor generation itself. The her gene network is partially redundant, with Notch-independent her genes better substituting for loss of Notch-dependent genes than vice versa. Together, her gene regulatory feedback loops and crossregulation contribute to the observed robustness of NSC maintenance.

developmental biology↗

bioRxiv2022

Selective endocytosis controls slit diaphragm maintenance and dynamics.

The kidneys generate about 180 liters of primary urine per day by filtration of plasma. An essential part of the filtration barrier is the slit diaphragm, a multiprotein complex containing nephrin as major component. Filter dysfunction typically manifests with proteinuria and mutations in endocytosis regulating genes were discovered as causes of proteinuria. However, it is unclear how endocytosis regulates the slit diaphragm and how the filtration barrier is maintained without either protein leakage or filter clogging. Here we study nephrin dynamics in podocyte-like nephrocytes of Drosophila and show that selective endocytosis either by dynamin- or flotillin-mediated pathways regulates a stable yet highly dynamic architecture. Short-term manipulation of endocytic functions indicates that dynamin-mediated endocytosis of ectopic nephrin restricts slit diaphragm formation spatially while flotillin-mediated turnover of nephrin within the slit diaphragm is needed to maintain filter permeability by shedding of molecules bound to nephrin in endosomes. Since slit diaphragms cannot be studied in vitro and are poorly accessible in mouse models, this is the first analysis of their dynamics within the slit diaphragm multiprotein complex. Identification of the mechanisms of slit diaphragm maintenance will help to develop novel therapies for proteinuric renal diseases that are frequently limited to symptomatic treatment.

cell biology↗

bioRxiv2020

The superoxide dismutase mimetic GC4419 enhances tumor killing when combined with stereotactic ablative radiation

The penta-aza macrocyclic manganese compound GC4419 is in phase 3 clinical trials as a modifier of mucositis in H&N cancer treated by radio-chemotherapy based upon its properties as a superoxide dismutase mimetic. In studies to address the potential for tumor radioprotection, a significant anti-tumor effect was identified in tumors generated from the non-small cell lung cancer (NSCLC) cell line H1299, when GC4419 was combined with radiation. This effect was directly related to the size of the radiation dose as demonstrated by greater efficacy in tumor growth delay when biologically equivalent irradiation regimens using a limited number of dose fractions was substantially more effective compared to regimens where the fraction number was higher and dose per fraction decreased. Furthermore, a TCD50 assay using H1299 tumors that tested the combination of GC4419 with radiation revealed a Dose Enhancement Factor of 1.67. Based upon these results the hypothesis that GC4419 was generating cytotoxic levels of hydrogen peroxide during the superoxide dismutation process. Peroxide flux did increase in cells exposed to GC4419 as did the expression of the oxidative stress markers 4-HNE and 3-NT. H1299 cells that overexpressed catalase were then challenged as tumors by the combination of radiation and GC4419 and the tumoricidal effect was nearly eliminated. The enhanced radiation response was not specific to NSCLC as similar findings were observed in human head and neck squamous cell carcinoma and pancreatic ductal adenocarcinoma xenografts. RNA sequencing analysis revealed that GC4419, in addition to generating high levels of hydrogen peroxide in irradiated cells, alters inflammatory and differentiation signaling in the tumor following irradiation. Together, these findings provide abundant evidence that the radioprotector GC4419 has dual functionality and will increase tumor response rates when combined with agents that generate high levels of superoxide like stereotactic ablative body radiotherapy (SAbR). Combining SAbR with GC4419 may be an effective strategy to enhance tumor response in general but may also allow for fully potent radiation doses to tumors that might not necessarily be able to tolerate such doses. The potential for protection of organs at risk may also be exploitable.

cancer biology↗