mTOR and Myosin Vb shape epithelia during development

To maintain the architecture and integrity of the epithelium throughout development, cells need to regulate their size and morphology. This is achieved through the synthesis of plasma membrane components, but it has so far remained unclear how this process is coordinated with the transport of lipids to the membrane. Now, Mahendra Sonawane and co-workers show that the Myosin VB motor is central to this process in the developing zebrafish epidermis. They demonstrate that the interaction of Myosin Vb with Rab10 is required for the maintenance of trans-Golgi network (TGN) organisation. Upon disruption of the Myosin Vb-Rab10 interaction, transport from the Golgi to the plasma membrane is inhibited, leading to the accumulation and degradation of presumably membranogenic vesicles. Although this does not affect the epithelium during development, lack of the Myosin Vb-Rab10 interaction prevents apical cell growth during compensatory hypertrophy in epidermal cells. Interestingly, the authors find that inhibition of mTOR signalling also prevents apical growth during compensatory hypertrophy. Moreover, the authors observe an enlargement of the TGN upon loss of the Myosin Vb-Rab10 interaction, which results from an mTOR-dependent increase in lipid synthesis. Together, these results indicate that the trans-Golgi network integrates plasma membrane synthesis with lipid transport by coordinating mTOR signalling with the activity of Myosin Vb-Rab10.