Biology subjects

Montell, D. J.

Publications and source records attributed to Montell, D. J..

8 recordsLinked to original sources

bioRxiv2026

Rac2 Hyperactivity Drives Neutrophil Degranulation, Myeloperoxidase Deficiency, and Lymphopenia

Patients with a dominant mutation in the Rho GTPase RAC2, RAC2E62K, which hyperactivates the protein, suffer from a combined immunodeficiency characterized by recurrent bacterial and fungal infections and severe T cell lymphopenia. Patient neutrophils have elevated F-actin and superoxide production yet fail to control growth of S. aureus, and the mechanism underlying this killing defect is unknown. Here we report that hyperactive Rac2 primes neutrophils for primary granule degranulation, potentially depleting myeloperoxidase (MPO) needed for intraphagosomal microbial killing. Using a Rac2+/E62K mouse model, we show that mature bone marrow neutrophils have decreased side scatter, elevated surface CD63, and reduced intracellular MPO. Interestingly, bone marrow architecture and neutrophil development in the mice are normal. Rac2+/E62K neutrophils are hyperactivated, with increased CD11b expression, cell spreading, and bioparticle phagocytosis. In the spleen, Rac2+/E62K mice display extramedullary granulopoiesis and an accumulation of degranulating neutrophils. Splenic T cells, but not B cells, show elevated surface phosphatidylserine, an "eat me" signal that sensitizes them to phagocytic clearance and provides a candidate mechanism for the selective T cell lymphopenia. Together these findings suggest that hyperactive Rac2 compromises antimicrobial neutrophil function and drives selective T cell clearance in the spleen.

immunology↗

bioRxiv2026

Systematic analysis of RhoGAP expression and function in border cell morphology and migration

Rho family GTPases are central hubs in the signaling and cytoskeletal networks that govern cell morphology and behavior. GTPase-activating proteins (GAPs) inactivate them by accelerating GTP hydrolysis. However, a systematic analysis of GAPs in cell migration is lacking. Here, we report screens for RhoGAP expression and function in migratory Drosophila border cells. Constitutively active Cdc42, Rac, or Rho causes defects, demonstrating that negative regulation is critical. Integrating single-cell RNAseq with published datasets reveals that most of the 22 RhoGAPs are expressed in border cells. RNAi knockdown shows most RhoGAPs are functionally required. We developed automated image analysis tools to sensitively and objectively classify border cell morphologies, defining a normal morphological phase space. RhoGAP perturbations push clusters outside this range. In-depth analysis of RhoGAPp190 reveals that loss-of-function resembles Rho hyperactivation and gain-of-function resembles myosin II inhibition. Thus, complex spatiotemporal sculpting of RhoGTPase activities requires diverse RhoGAPs within a single cell type to control morphology and motility in vivo.

cell biology↗

bioRxiv2026

NG2-targeting macrophages inhibit 3D invasion of patient-derived glioblastoma spheroids

Engineering macrophages with chimeric antigen receptors is emerging as a promising cancer therapeutic. Chimeric antigen receptor-expressing macrophages (CAR-Ms) engineered to recognize tumor-specific antigens have been shown to inhibit tumor growth and activate adaptive immune responses, leading to robust tumor control in animal studies. Based on this work, clinical trials have been initiated. While the trials have shown promise, challenges remain. The dynamic interactions between CAR-Ms and cancer cells and the exact mechanisms driving anti-tumor effects remain poorly defined. Defining the dynamic interactions between CAR-Ms and cancer cells will provide critical insights for optimizing future CAR-M design and improving therapeutic efficacy. We sought to directly visualize CAR-M interactions with glioblastoma cells at high-resolution and in real-time using CAR-Ms engineered to recognize Neural-Glial Antigen 2 (NG2), an antigen expressed on glioblastoma cells. Using patient-derived glioblastoma cells, we formed glioblastoma spheroids and embedded them in a 3D matrix together with CAR-Ms. Using time-lapse microscopy, as expected, we found that NG2-targeting CAR-Ms engulfed glioblastoma cells. However, excitingly, we found that NG2-targeting CAR-Ms blocked >85% of glioblastoma cell invasion in 3D. This inhibition of glioblastoma invasion was not due to a significant change in CAR-M polarization states. Together, these data suggest that NG2-targeting CAR-Ms both engulf glioblastoma cells and block glioblastoma invasive behavior.

cancer biology↗

bioRxiv2025

CD47 prevents Rac-mediated phagocytosis through Vav1 dephosphorylation

CD47 is expressed by viable cells to protect against phagocytosis. CD47 is recognized by SIRP, an inhibitory receptor expressed by macrophages and other myeloid cells. Activated SIRP recruits SHP-1 and SHP-2 phosphatases but the inhibitory signaling cascade downstream of these phosphatases is not clear. In this study, we used time lapse imaging to measure how CD47 impacts the kinetics of phagocytosis. We found that targets with IgG antibodies were primarily phagocytosed through a Rac-based reaching mechanism. Targets also containing CD47 were only phagocytosed through a less frequent Rho-based sinking mechanism. Hyperactivating Rac2 eliminated the suppressive effect of CD47, suggesting that CD47 prevents activation of Rac and reaching phagocytosis. During IgG-mediated phagocytosis, the tyrosine kinase Syk phosphorylates the GEF Vav, which then activates the GTPase Rac to drive F-actin rearrangement and target internalization. CD47 inhibited Vav1 phosphorylation without impacting Vav1 recruitment to the phagocytic synapse or Syk phosphorylation. Macrophages expressing a hyperactive Vav1 were no longer sensitive to CD47. Together this data suggests that Vav1 is a key target of the CD47 signaling pathway.

cell biology↗

bioRxiv2022

Specialized protrusions coordinate migratory border cell cluster cohesion via Scribble, Cdep, and Rac

Collective cell movements drive normal development and metastasis. Drosophila border cells move as a cluster of 6-10 cells, where the role of the Rac GTPase in migration was first established. Rac stimulates leading edge protrusions in most migratory cells. Upstream Rac regulators in leading border cell protrusions have been identified; however the regulation and function of Rac in follower cells is unknown. Here we show that Rac is required in all cells of the cluster and promotes follower cell motility. We identify a Rac guanine nucleotide exchange factor, Cdep, that also regulates follower cell movement and cluster cohesion. The tumor suppressors Scribble, Discs Large, and Lethal Giant Larva localize Cdep basolaterally and share phenotypes with Cdep. Relocalization of Cdep::GFP partially rescues Scrib knockdown, suggesting that Cdep is a major downstream effector of basolateral proteins. Thus, a Scrib/Cdep/Rac pathway promotes cell crawling and coordinated, collective migration in vivo.

cell biology↗

bioRxiv2021

Septins are essential for protrusion and detachment in collective border cell migration

Septins self-assemble into polymers that bind and deform membranes in vitro and regulate diverse cell behaviors in vivo. How their in vitro properties relate to their in vivo functions is under active investigation. Here we uncover requirements for septins in detachment and motility of border cell clusters in the Drosophila ovary. Septins and myosin colocalize dynamically at the cluster periphery and share phenotypes, but surprisingly do not impact each other. Instead, Rho independently regulates myosin activity and septin localization. Active Rho recruits septins to membranes while inactive Rho sequesters septins in the cytoplasm. Mathematical analyses reveal how manipulating septin expression alters cluster shape and surface geometry. This study shows that the level of septin expression regulates surface properties at different scales. This work suggests that downstream of Rho, septins tune surface deformability while myosin controls contractility, the combination of which govern cluster shape and movement.

cell biology↗

bioRxiv2017

Stem cell niche signals Wnt, Hedgehog, and Notch distinctively regulate Drosophila follicle precursor cell differentiation

Adult stem cells commonly give rise to transit-amplifying progenitors, whose progeny differentiate into distinct cell types. Signals within the stem cell niche maintain the undifferentiated state. However it is unclear whether or how niche signals might also coordinate fate decisions within the progenitor pool. Here we use quantitative microscopy to elucidate distinct roles for Wnt, Hedgehog (Hh), and Notch signalling in progenitor development in the Drosophila ovary. Follicle stem cells (FSCs) self-renew and produce precursors whose progeny adopt distinct polar, stalk, and main body cell fates. We show that a steep gradient of Wnt signalling maintains a multipotent state in proximally located progenitor cells by inhibiting expression of the cell fate determinant Eyes Absent (Eya). A shallower gradient of Hh signalling controls the proliferation to differentiation transition. The combination of Notch and Wnt signalling specifies polar cells. These findings reveal a mechanism by which multiple niche signals coordinate cell fate diversification of progenitor cells.

developmental biology↗

bioRxiv2017

A Molecular Signature for Anastasis, Recovery from the Brink of Apoptotic Cell Death

During apoptosis, executioner caspase activity has been considered a point of no return. However, recent studies show that cells can survive caspase activation following transient apoptotic stimuli, a process named anastasis. To identify a molecular signature, we performed whole transcriptome RNA sequencing of untreated, apoptotic, and recovering HeLa cells. We found that anastasis is an active, two-stage program. During the early stage, cells transition from growth-arrested to growing. In the late stage, cells change from proliferating to migratory. Strikingly, some early recovery mRNAs were elevated first during apoptosis, implying that dying cells poise to recover, even while still under apoptotic stress. Furthermore, TGF{beta}-induced Snail expression is required for anastasis, and recovering cells exhibit prolonged elevation of pro-angiogenic factors. This study demonstrates similarities in the anastasis genes, pathways, and cell behaviors to those activated in wound healing. This study identifies a repertoire of potential targets for therapeutic manipulation of this process.

cell biology↗