Mutant DMPK 3′-UTR transcripts disrupt C2C12 myogenic differentiation by compromising MyoD

Myotonic dystrophy (DM) is caused by two similar noncoding repeat expansion mutations (DM1 and DM2). It is thought that both mutations produce pathogenic RNA molecules that accumulate in nuclear foci. The DM1 mutation is a CTG expansion in the 3′ untranslated region (3′-UTR) of dystrophia myotonica protein kinase (DMPK). In a cell culture model, mutant transcripts containing a (CUG)200 DMPK 3′-UTR disrupt C2C12 myoblast differentiation; a phenotype similar to what is observed in myoblast cultures derived from DM1 patient muscle. Here, we have used our cell culture model to investigate how the mutant 3′-UTR RNA disrupts differentiation. We show that MyoD protein levels are compromised in cells that express mutant DMPK 3′-UTR transcripts. MyoD, a transcription factor required for the differentiation of myoblasts during muscle regeneration, activates differentiation-specific genes by binding E-boxes. MyoD levels are significantly reduced in myoblasts expressing the mutant 3′-UTR RNA within the first 6 h under differentiation conditions. This reduction correlates with blunted E-box–mediated gene expression at time points that are critical for initiating differentiation. Importantly, restoring MyoD levels rescues the differentiation defect. We conclude that mutant DMPK 3′-UTR transcripts disrupt myoblast differentiation by reducing MyoD levels below a threshold required to activate the differentiation program

Tissue flow induces cell shape changes during organogenesis

In embryonic development, programmed cell shape changes are essential for building functional organs, but in many cases the mechanisms that precisely regulate these changes remain unknown. We propose that fluid-like drag forces generated by the motion of an organ through surrounding tissue could generate changes to its structure that are important for its function. To test this hypothesis, we study the zebrafish left-right organizer, Kupffer's vesicle (KV), using experiments and mathematical modeling. During development, monociliated cells that comprise the KV undergo region-specific shape changes along the anterior-posterior axis that are critical for KV function: anterior cells become long and thin, while posterior cells become short and squat. Here, we develop a mathematical vertex-like model for cell shapes, which incorporates both tissue rheology and cell motility, and constrain the model parameters using previously published rheological data for the zebrafish tailbud [Serwane et al.] as well as our own measurements of the KV speed. We find that drag forces due to dynamics of cells surrounding the KV could be sufficient to drive KV cell shape changes during KV development. More broadly, these results suggest that cell shape changes could be driven by dynamic forces not typically considered in models or experiments

CEP162 is an axoneme-recognition protein promoting ciliary transition zone assembly at the cilia base

The transition zone (TZ) is a specialized compartment found at the base of cilia, adjacent to the centriole distal end, where axonemal microtubules (MTs) are heavily cross-linked to the surrounding membrane to form a barrier that gates the ciliary compartment. A number of ciliopathy molecules have been found to associate with the TZ, but factors that directly recognize axonemal MTs to specify TZ assembly at the cilia base remain unclear. Here, through quantitative centrosome proteomics, we identified an axoneme-associated protein, CEP162, tethered specifically at centriole distal ends to promote TZ assembly. CEP162 interacts with core TZ components, and mediates their association with MTs. Loss of CEP162 arrests ciliogenesis at the stage of TZ assembly. Abolishing its centriolar tethering, however, allows CEP162 to stay on the growing end of the axoneme, and ectopically assemble TZ components at cilia tips. This generates extra-long cilia with strikingly swollen tips that actively release ciliary contents into the extracellular environment. CEP162 is thus an axoneme-recognition protein “pre-tethered” at centriole distal ends prior to ciliogenesis to promote and restrict TZ formation specifically at the cilia base

Prostaglandin signalling regulates ciliogenesis by modulating intraflagellar transport

Cilia are microtubule-based organelles that mediate signal transduction in a variety of tissues. Despite their importance, the signalling cascades that regulate cilium formation remain incompletely understood. Here we report that prostaglandin signalling affects ciliogenesis by regulating anterograde intraflagellar transport (IFT). Zebrafish leakytail (lkt) mutants show ciliogenesis defects, and the lkt locus encodes an ATP-binding cassette transporter (ABCC4). We show that Lkt/ABCC4 localizes to the cell membrane and exports prostaglandin E2 (PGE2), a function that is abrogated by the Lkt/ABCC4T804M mutant. PGE2 synthesis enzyme cyclooxygenase-1 and its receptor, EP4, which localizes to the cilium and activates the cyclic-AMP-mediated signalling cascade, are required for cilium formation and elongation. Importantly, PGE2 signalling increases anterograde but not retrograde velocity of IFT and promotes ciliogenesis in mammalian cells. These findings lead us to propose that Lkt/ABCC4-mediated PGE2 signalling acts through a ciliary G-protein-coupled receptor, EP4, to upregulate cAMP synthesis and increase anterograde IFT, thereby promoting ciliogenesis

Methods from Cilia in vertebrate left–right patterning

Creating and imaging of mosaic labeled dorsal forerunner cells (DFCs) in live zebrafish embryo

Time-lapse imgaing of KV development from Cilia in vertebrate left–right patterning

Time-lapse video microscopy during DFC to KV transition. Confocal time-lapse video imaging of mosaic labeled DFC/KV cells from Tg(ubi:Zebrabow);Tg(sox17:CreERT2) double transgenic embryos. Cell behaviors were monitored for 60 min. starting at 90% epiboly stage. This developmental window includes migration and rearrangement of cells within DFC cluster and consequent KV lumen formation. Cells do not rearrange stochastically, but rather prefer to maintain their positional information during DFC to KV morphogenesis

Methods from Cilia in vertebrate left–right patterning

Creating and imaging of mosaic labeled dorsal forerunner cells (DFCs) in live zebrafish embryo

Evolution and Expression of Paxillin Genes in Teleost Fish.

BACKGROUND:Paxillin family proteins regulate intracellular signaling downstream of extracellular matrix adhesion. Tissue expression patterns and cellular functions of Paxillin proteins during embryo development remain poorly understood. Additionally, the evolution of this gene family has not been thoroughly investigated. RESULTS:This report characterizes the evolution and expression of a novel Paxillin gene, called Paxillin-b, in Teleosts. Alignments indicate that Teleost Paxillin-a and Paxillin-b proteins are highly homologous to each other and to human Paxillin. Phylogenetic and synteny analyses suggest that these genes originated from the duplication of an ancestral Paxillin gene that was in a common ancestor of Teleosts and Tetrapods. Analysis of the spatiotemporal expression profiles of Paxillin-a and Paxillin-b using zebrafish revealed both overlapping and distinct domains for Paxillin-a and Paxillin-b during embryo development. Localization of zebrafish Paxillin orthologs expressed in mammalian cells demonstrated that both proteins localize to focal adhesions, similar to mammalian Paxillin. This suggests these proteins regulate adhesion-dependent processes in their endogenous tissues. CONCLUSION:Paxillin-a and Paxillin-b were generated by duplication in Teleosts. These genes likely play similar roles as Paxillin genes in other organisms. This work provides a framework for functional investigation of Paxillin family members during development using the zebrafish as an in vivo model system