Biology subjects

Louka, P.

Publications and source records attributed to Louka, P..

4 recordsLinked to original sources

bioRxiv2026

Regulation and function of trans-physeal growth plate bridges: evidence for a mechanical base isolation role to minimise epiphyseal shear stress

The cartilaginous growth plate (GP) is responsible for all bone elongation during post-natal growth yet must simultaneously contribute to mechanical epiphyseal stability for articulation. How the GP balances these dual functions across the bone-cartilage-bone epiphyseal interface during complex load-growth transitions is not defined. Herein, we examine regulation and mechanobiology of GP bridges - mineralised trans-physeal GP structures - to explore whether they serve these dual GP functions. We have determined the effects of age and sex, short- and long-term joint loading and several established and new osteotropic pharmacological agents on mouse tibial GP bridge number and areal density using micro-computed tomography. We also explored temporal formation and progression of GP bridges by serial in vivo scanning and we imaged epiphyseal load-transfer in young and mature mice in situ via synchrotron X-ray computed tomography (sCT) of intact joints under physiologically oriented load. Our utilisation of digital volume correlation revealed regional 3D load-induced strain inhomogeneities in the GP that are synchronised to bridge location and this was substantiated using finite element modelling. Furthermore, direct micro- and sCT examinations showed that bridges consistently contain a singular epiphyseal/metaphyseal discontinuity which appear to serve a novel mechanical base isolation role to minimise shear stress across the GP. Our data indicate that bridges are regulatable, dynamic structures that synchronise GP strains and exhibit sensitivity to local joint mechanics. We highlight that trans-physeal bridges may contribute to longitudinal bone growth cessation whilst simultaneously stabilising the epiphysis by absorbing compression and shear strains.

bioengineering↗

bioRxiv2025

SPEF1 mediates assembly of the central pair microtubule complexes in cilia of Tetrahymena.

SPEF1 is a conserved protein that reinforces the seam of central microtubules within the distal segment of motile cilia. We show that in Tetrahymena, loss of SPEF1 destabilized the central pair throughout the cilium length, producing gaps in the microtubule lattice, loss of proximal microtubule portions, and loss of lateral projections. While both central microtubules were affected, C1 suffered more damage than C2 and the defects were already apparent during ciliary assembly. Tetrahymena cells lacking SPEF1 had fewer cilia, which contained an excessively dense ciliary matrix and abnormal densities on the doublet microtubules. Although SPEF1 loss visibly affected only the central microtubules, it localized to all stable microtubules in the cell, both ciliary and non-ciliary. Within cilia, SPEF1 was enriched near the distal tip, but was also present throughout the middle segment, where it was more concentrated along the central than the outer doublet microtubules. In live cilia, SPEF1 particles were mostly stationary and turned over slowly, some diffused but none moved by IFT. We propose that SPEF1 acts as a stabilizer of central microtubules in both the middle and distal segment and its activity contributes to central microtubule assembly.

cell biology↗

bioRxiv2025

Ciliary and non-ciliary functions of CEP104 in Xenopus

Cep104 is a conserved protein essential for centriole and cilia function, with mutations linked to Joubert Syndrome. We investigated its role in Xenopus embryonic development, revealing that Cep104 is crucial for neural tube closure (NTC) through regulating apical constriction. We show that the role of Cep104 in cilia and hedgehog signaling cannot alone explain the elicited defects. We go on to show that Cep104 localizes to the ends of cytoplasmic microtubules, influencing their stability. Downregulation of CEP104 led to microtubule instability and defects in multiciliated cell intercalation, a process dependent on stable microtubules. Our findings demonstrate that Cep104 functions beyond cilia, playing a significant role in cytoplasmic microtubule dynamics, suggesting that both ciliary and non-ciliary roles are important for neurodevelopment and the pathogenesis of ciliopathies.

cell biology↗

bioRxiv2018

Tetrahymena RIB72A and RIB72B are Microtubule Inner Proteins in the ciliary doublet microtubules

Doublet and triplet microtubules are essential and highly stable core structures of centrioles, basal bodies, cilia and flagella. In contrast to dynamic cytoplasmic microtubules, their luminal surface is coated with regularly arranged Microtubule Inner Proteins (MIPs). However, the protein composition and biological function(s) of MIPs remain poorly understood. Using genetic, biochemical and imaging techniques we identified Tetrahymena RIB72A and RIB72B proteins as ciliary MIPs. Fluorescence imaging of tagged RIB72A and RIB72B showed that both proteins co-localize to Tetrahymena cilia and basal bodies, but assemble independently. Cryo-electron tomography of RIB72A and/or RIB72B knockout strains revealed major structural defects in the ciliary A-tubule involving MIP1, MIP4 and MIP6 structures. The defects of individual mutants were complementary in the double mutant. All mutants had reduced swimming speed and ciliary beat frequencies, and high-speed video imaging revealed abnormal highly curved cilia during power stroke. Our results show that RIB72A and RIB72B are crucial for the structural assembly of ciliary A-tubule MIPs and are important for proper ciliary motility.\n\nSUMMARYMicrotubule Inner Proteins (MIPs) bind to the luminal surface of highly stable microtubules. Combining cell biology and cryo-electron tomography, Stoddard et al. show that RIB72A and RIB72B are conserved MIPs in ciliary doublet microtubules and that they are important for proper ciliary motility.

cell biology↗