The activation of the mTOR pathway supports lysosome biogenesis in the sea urchin embryo

The mTOR pathway controls the balance between anabolic and catabolic activities in animal cells, acting as a key coordinator of metabolic homeostasis. In fact, the activation of this conserved regulatory circuit promotes the biosynthesis of different macromolecules, including proteins, lipids and nucleic acids, and blocks simultaneously catabolic processes such as lysosome biogenesis. In this work we describe a biological system in which these two aspects of the mTOR function are uncoupled. Studying the sea urchin Paracentrotus lividus, we have found that the activation of the mTOR pathway in the fertilised egg, besides stimulating protein synthesis, contributes to the development of a dense array of acidic vesicles that behave as lysosomes. We present evidence indicating that mTOR could operate in this context enhancing the translation of the maternal transcripts that code for the multiple components of these organelles. We argue that the mTOR-mediated implementation of a typical catabolic process may in fact support the biosynthetic vocation of this pathway, providing energy and recycled blocks for construction.