CLASP2-dependent microtubule capture at the neuromuscular junction membrane requires LL5β and actin for focal delivery of acetylcholine receptor vesicles.

A hallmark of the neuromuscular junction (NMJ) is the high density of acetylcholine receptors (AChRs) in the postsynaptic muscle membrane. The postsynaptic apparatus of the NMJ is organized by agrin secreted from motor neurons. The mechanisms that underlie the focal delivery of AChRs to the adult NMJ are not yet understood in detail.

Acetylcholine receptor (AChR) clustering is regulated both by glycogen synthase kinase 3β (GSK3β)-dependent phosphorylation and the level of CLIP-associated protein 2 (CLASP2) mediating the capture of microtubule plus-ends.

The postsynaptic apparatus of the neuromuscular junction (NMJ) traps and anchors acetylcholine receptors (AChRs) at high density at the synapse. We have previously shown that microtubule (MT) capture by CLASP2, a MT plus-end-tracking protein (+TIP), increases the size and receptor density of AChR clusters at the NMJ through the delivery of AChRs and that this is regulated by a pathway involving neuronal agrin and several postsynaptic kinases, including GSK3. Phosphorylation by GSK3 has been shown to cause CLASP2 dissociation from MT ends, and nine potential phosphorylation sites for GSK3 have been mapped on CLASP2.

Agrin regulates CLASP2-mediated capture of microtubules at the neuromuscular junction synaptic membrane.

Agrin is the major factor mediating the neuronal regulation of postsynaptic structures at the vertebrate neuromuscular junction, but the details of how it orchestrates this unique three-dimensional structure remain unknown. Here, we show that agrin induces the formation of the dense network of microtubules in the subsynaptic cytoplasm and that this, in turn, regulates acetylcholine receptor insertion into the postsynaptic membrane. Agrin acted in part by locally activating phosphatidylinositol 3-kinase and inactivating GSK3β, which led to the local capturing of dynamic microtubules at agrin-induced acetylcholine receptor (AChR) clusters, mediated to a large extent by the microtubule plus-end tracking proteins CLASP2 and CLIP-170.

Beta-catenin/LEF-1 signalling in breast cancer--central players activated by a plethora of inputs.

Although the role of Wnt signalling in breast cancer is far from being fully understood, in the last years its importance has been reported frequently. Besides stimulation by canonical Wnt signalling, the downstream effectors beta-catenin and the transcriptional modulators of the T-cell factor/lymphoid enhancer-binding factor (TCF/LEF) family can also be activated by other inputs including the TGF-beta pathway. Wnt and TGF-beta signalling are both major signal transduction pathways, which provide important cues during development and tumor progression.