Richardson, L. B. | bioRxiv Science

bioRxiv2026

SSNA1 mechanically reinforces the damaged microtubule lattice

SSNA1 (Sjogrens Syndrome Nuclear Autoantigen 1) is a microtubule-associated protein involved in key cellular processes, including cell division, intraflagellar transport, and axonal branching. SSNA1 specifically localizes to sites of damage along the microtubule lattice, thus acting as a microtubule damage sensor. However, the effects of SSNA1 on microtubule mechanics or on the process of microtubule self-repair, which involves the incorporation of soluble tubulin dimers into lattice damage sites, are not known. Here, we use in vitro reconstitution with purified proteins and total internal reflection fluorescence (TIRF) microscopy to probe SSNA1s effects on microtubule mechanics and self-repair. We apply two distinct sources of force to investigate microtubule mechanics: kinesin-driven gliding assays and microfluidic flow. We find that SSNA1 binding increases microtubule rigidity and resistance to breakage under the physiological and controlled forces in our assays. Interestingly, SSNA1s localization to microtubule damage sites prevents the incorporation of new tubulin dimers and thus inhibits lattice self-repair. Conversely, we find that SSNA1 does not recognize damage sites that have been repaired by tubulin incorporation. Together, our findings demonstrate that SSNA1 reinforces the mechanical strength of microtubules without promoting self-repair, suggesting an alternative mechanism for restoring microtubule integrity in the absence of tubulin-mediated repair and providing new insights into SSNA1s mechanism of microtubule stabilization. Significance StatementMicrotubules are cytoskeletal polymers that experience mechanical stress during essential cellular processes such as cargo transport, cell division, and ciliary beating. To maintain their integrity, microtubules rely on both stabilizing proteins and repair mechanisms. Here, we show that microtubule-associated protein SSNA1 strengthens microtubules by increasing their rigidity and resistance to force-induced breakage, while simultaneously blocking tubulin-mediated lattice repair at sites of damage. By distinguishing between damaged and repaired microtubule lattices, SSNA1 enforces a stabilization strategy that favors mechanical reinforcement over self-repair. These findings reveal a new mode of microtubule regulation that decouples mechanical stability from lattice repair and provide insight into how cells preserve cytoskeletal integrity under force.

biophysics↗

bioRxiv2025

Disentangling local adaptation and phenotypic plasticity in traits associated with altitude and temperature in widespread tropical butterflies

Climatic stratifications, in particular differences in temperature, occur along altitudinal clines. Understanding genetic and phenotypic divergence across these regions can give insight into speciation and diversification, as well as aid in our knowledge of how species may respond to possible climate change scenarios. Most past research has focused on temperate regions, yet it is in the tropics that organisms are thought to be the most vulnerable to rising temperatures. In addition, year-round stable temperatures in the tropics make altitudinal temperature variation more pronounced and increase the likelihood of local adaptation across relatively narrow gradients. Here we investigate how genetics and the environment influence a wide range of traits in two butterfly species, Heliconius erato and Heliconius melpomene, which are widespread across the neotropics and occur along the altitudinal slope of the Andes. Using common garden rearing of over 1,000 offspring from over 70 wild females caught along an altitudinal gradient, as well as rearing of populations from either end of the altitudinal range in their reciprocal temperature environments, we find evidence of genetic, environmental, and in some cases gene-by-environment interaction effects in developmental, morphological, and thermal tolerance traits. We find parallel divergence in wing colour in both species, with wing colour darkening with increasing altitude, consistent with this playing a role in thermoregulation in these species where wing colour has mostly been linked to mimicry and mate choice. We also find evidence for gene-by-environment interactions: In H. erato we found local differences in heat acclimation response, with increased heat knock-out times at higher rearing temperatures found only in low altitude populations, which are exposed to the hottest temperatures. We find evidence for heritable genetic variation in most traits measured, with positive implications for adaptation to climate change, although our results suggest that selection may not act in a straightforward way on these traits.

ecology↗