Biology subjects

Tipping, M. J.

Publications and source records attributed to Tipping, M. J..

4 recordsLinked to original sources

bioRxiv2026

Microscale Characterization of Undecalcified Bone Tissue Using Correlative Atomic Force Microscopy and Histology

Characterizing bone tissue in its mineralized state remains technically challenging. Conventional approaches typically compromise mechanical integrity through decalcification or lack the structural resolution necessary to capture microscale heterogeneity. Here we present an integrated workflow combining atomic force microscopy (AFM) with histological and immunofluorescence assays on adjacent undecalcified bone tissue cryosections. Using a tape-transfer mounting approach, we resolve mechanically and structurally distinct tissue types within a minimally processed single mouse femur section. Furthermore, we show that decalcification substantially alters nanoscale surface topography and local mechanical properties. Applied to an aging cohort of C57BL/6J female mice spanning 7 to 115 weeks, the proposed method detects age-associated changes in bone matrix structure and stiffness. The approach provides a practical methodology for spatially correlating nanomechanical properties with molecular markers in bone and other mineralized tissues, with broad applicability to disease models including cancer metastasis, osteoporosis, and osteoarthritis.

biophysics↗

bioRxiv2024

Invasion of glioma cells through confined space requires membrane tension regulation and mechano-electrical coupling via Plexin-B2

Glioblastoma (GBM) is a malignant brain tumor with uncontrolled invasive growth. Here, we demonstrate how GBM cells usurp guidance receptor Plexin-B2 to gain biomechanical plasticity for polarized migration through confined space. Using live-cell imaging to track GBM cells negotiating microchannels, we reveal active endocytosis at cell front and filamentous actin assembly at rear to propel GBM cells through constrictions. These two processes are interconnected and governed by Plexin-B2 that orchestrates cortical actin and membrane tension, shown by biomechanical assays. Molecular dynamics simulations predict that balanced membrane and actin tension are required for optimal migratory velocity and consistency. Furthermore, Plexin-B2 mechanosensitive function requires a bendable extracellular ring structure and affects membrane internalization, permeability, phospholipid composition, as well as inner membrane surface charge. Together, our studies unveil a key element of membrane tension and mechanoelectrical coupling via Plexin-B2 that enables GBM cells to adapt to physical constraints and achieve polarized confined migration.

cancer biology↗

bioRxiv2018

Peer pressure from a Proteus mirabilis self-recognition system controls participation in cooperative swarm motility

Colonies of the opportunistic pathogen Proteus mirabilis can distinguish self from non-self: in swarming colonies of two different strains, one strain excludes the other from the expanding colony edge. Predominant models characterize bacterial kin discrimination as immediate antagonism towards non-kin cells, typically through delivery of toxin effector molecules from one cell into its neighbor. Upon effector delivery, receiving cells must either neutralize it by presenting a cognate anti-toxin, as would a clonal sibling, or suffer cell death or irreversible growth inhibition, as would a non-kin cell. Here we expand this paradigm to explain the non-lethal Ids self-recognition system, which stops access to a cooperative social behavior in P. mirabilis through a distinct mechanism: selectively and transiently inducing nonself cells into a lifestyle incompatible with cooperative swarming. This state is characterized by reduced expression of genes associated with protein synthesis, virulence, and motility, and also causes non-self cells to tolerate previously lethal concentrations of antibiotics. We found that entry into this state requires a temporary activation of the stringent response in non-self cells and results in the iterative exclusion of non-self cells as a swarm colony migrates outwards. These data clarify the intricate connection between non-lethal recognition and the lifecycle of P. mirabilis swarm colonies.

microbiology↗

bioRxiv2017

The Proteus mirabilis rffG gene is essential for swarm-associated cell elongation through an Rcs-mediated pathway

Individual cells of the bacterium Proteus mirabilis can elongate up to 40-fold on surfaces before engaging in a cooperative surface-based motility termed swarming. How cells regulate this dramatic morphological remodeling remains an open question. In this paper, we move forward the understanding of this regulation by demonstrating that P. mirabilis requires the gene rffG for swarmer cell elongation and subsequent swarm motility. The rffG gene encodes a protein homologous to the dTDP-glucose 4,6 dehydratase protein of Escherichia coli, which contributes to Enterobacterial Common Antigen biosynthesis. Here we characterize the rffG gene in P. mirabilis, demonstrating that it is required for the production of large lipopolysaccharide-linked moieties necessary for wild-type cell envelope integrity. We show that absence of the rffG gene induces several stress-responsive pathways including those controlled by the transcriptional regulators RpoS, CaiF, and RcsB. We further show that in rffG-deficient cells, suppression of the Rcs phosphorelay, via loss of RcsB, is sufficient to induce cell elongation and swarm motility. However, loss of RcsB does not rescue cell envelope integrity defects and instead results in abnormally shaped cells, including cells producing more than two poles. We conclude that a RcsB-mediated response acts to suppress emergence of shape defects in cell envelope-compromised cells, suggesting an additional role for RcsB in maintaining cell morphology under stress conditions. We further propose that the composition of the cell envelope acts as a checkpoint before cells initiate swarmer cell elongation and motility.\n\nImportance statementP. mirabilis swarm motility has been implicated in pathogenesis. We have found that cells deploy multiple uncharacterized strategies to handle cell envelope stress beyond the Rcs phosphorelay when attempting to engage in swarm motility. While RcsB is known to directly inhibit the master transcriptional regulator for swarming, we have shown an additional role for RcsB in protecting cell morphology. These data support a growing appreciation that the Rcs phosphorelay is a multi-functional regulator of cell morphology in addition to its role in microbial stress responses. These data also strengthen the paradigm that outer membrane composition is a crucial checkpoint for modulating entry into swarm motility. Furthermore, the rffG-dependent moieties provide a novel, attractive target for potential antimicrobials.

microbiology↗