Centrosomes are major microtubule organizing centres that set up an internal microtubule (MT) network contributing to cell shape and to the formation of the mitotic spindle during cell division. Rearrangement of this MT array can be dictated by the centrosome and occurs during cell adhesion, polarization and migration. However, little is known about what regulates centrosome assembly and maintenance. beta1-integrins are common cell surface receptors and we show that beta1-integrin signalling is necessary for modulation of centrosome dynamics. In an attempt to identify the downstream components of beta1-integrin signalling involved, we also discovered that the activation of focal adhesion kinase or integrin linked kinase are not required in maintaining centrosome integrity. This would indicate that a non-canonical signalling beta1-integrin pathway might be involved in controlling centrosomal dynamics. This gives us greater insight into the mechanisms that control centrosomal stability and may lead to the better understanding of diseases like cancer and diseases, i.e. lissencephaly, which involve defects in cell polarization and asymmetric cell division, where the centrosome seems to have an important role.

Microtubules play a major role in intracellular trafficking of vesicles in endocrine cells. Detailed knowledge of microtubule organization and their relation to other cell constituents is crucial for understanding cell function. However, their role in insulin transport and secretion is currently under debate. Here, we use Fib-Sem to image islet beta cells in their entirety with unprecedented resolution. We reconstruct mitochondria, Golgi apparati, centrioles, insulin secretory granules and micro-tubules of seven beta cells, and generate a comprehensive spatial map of microtubule-organelle interactions. We find that micro-tubules form non-radial networks that are predominantly not connected to either centrioles or endomembranes. Microtubule number and length, but not microtubule polymer density, vary with glucose stimulation. Furthermore, insulin secretory granules are enriched near the plasma membrane where they associate with microtubules. In summary, we provide the first 3D reconstructions of complete microtubule networks in primary mammalian cells together with evidence regarding their importance for insulin secretory granule positioning and thus supportive role in insulin secretion.

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