Fraher, S. | Search bioRxiv

bioRxiv2026

Myosin-9b Controls Epithelial Brush Border Architecture through Motility-Dependent RhoA Signaling

Genetic variations in the MYO9B gene have been associated with Crohn's disease, celiac disease, and ulcerative colitis. These diseases have been characterized as primarily immune disorders. However, the overall molecular basis for the influence of Myo9b in these diseases remains poorly understood. Using in vivo small intestine ileum and human cell culture models, we identify a molecular function for Myo9b in the regulation of epithelial brush border microvilli. Using live-cell super-resolution microscopy, we characterize the motility of Myo9b as it moves toward enriched puncta at the tips of microvilli and visualize its direct regulation of small GTPase signaling using an active RhoA biosensor. In Myo9b knockout cells, microvilli abundance and dynamics are altered, but the cells ultimately maintain the presence of microvilli and the appropriate incorporation of microvilli specific cytoskeletal to membrane regulators such as Ezrin. Alternatively, expression of the Myo9b-S1011A disease variant as the only genetic copy in human cells results in a total loss of microvilli and Ezrin apical localization. These results indicate that Myo9b is a critical regulator of epithelial cell morphology and microvilli. Further, our data establish that the S1011A disease variant disrupts microvilli in human cells, suggesting a potential mechanistic link to its involvement in disease states.

cell biology↗

bioRxiv2025

Neuroinflammation links the neurogenic and neurodegenerative phenotypes of Nrmt1-/- mice

It is widely thought that age-related damage is the single biggest contributing factor to neurodegenerative diseases. However, recent studies are beginning to indicate that many of these diseases may have developmental origins that become unmasked overtime. It has been difficult to prove these developmental origins, as there are still few known links between defective embryonic neurogenesis and progressive neurodegeneration. We have created a constitutive knockout mouse for the N-terminal methyltransferase NRMT1 (Nrmt1-/- mice). Nrmt1-/- mice display phenotypes associated with premature aging. Specifically in the brain, they exhibit age-related striatal and hippocampal degeneration, which is accompanied by impaired short and long-term memory. These phenotypes are preceded by depletion of the postnatal neural stem cell (NSC) pools, which appears to be driven by their premature differentiation and migration. However, this differentiation is often incomplete, as many resulting neurons cannot permanently exit the cell cycle and ultimately undergo apoptosis. Here, we show that the onset of apoptosis corresponds to increased cleavage of p35 into the CDK5 activator p25, which can promote neuroinflammation. Accordingly, Nrmt1-/- brains exhibit an increase in pro-inflammatory cytokine signaling, astrogliosis, complement activation, microgliosis, and markers of a compromised blood brain barrier, all of which indicate an activated neuroimmune response. We also find Nrmt1-/- mice do not activate a corresponding anti-inflammatory response. These data indicate that abnormal neurogenesis can trigger neuroinflammation, which in the absence of compensatory anti-inflammatory signaling, could lead to neuronal apoptosis and progressive neurodegeneration.

neuroscience↗