Dynamic local mRNA distribution and translation influence the postnatal molecular maturation of perivascular astrocytic processes

Astrocytes (the main glial cells in the brain) are highly ramified and send out perivascular processes (PvAPs) that entirely sheathe the brains blood vessels. PvAPs are equipped with an enriched molecular repertoire that sustains astrocytic regulatory functions at the vascular interface. In the mouse, PvAP development starts after birth and is essentially complete by postnatal day (P) 15. Progressive molecular maturation also occurs over this period, with the acquisition of proteins enriched in PvAPs. The mechanisms controlling the development and molecular maturation of PvAPs have not been extensively characterized. We reported previously that mRNAs are distributed unequally in mature PvAPs and are locally translated. Since dynamic mRNA distribution and local translation influence the cells polarity, we hypothesized that they might sustain the postnatal maturation of PvAPs. Here, we used a combination of molecular biology and imaging approaches to demonstrate that the development of PvAPs is accompanied by the transport of mRNA and polysomal mRNA into PvAPs, the development of a rough endoplasmic reticulum (RER) network and Golgi cisternae, and local translation. By focusing on genes and proteins that are selectively or specifically expressed in astrocytes, we characterized the developmental profile of mRNAs, polysomal mRNAs and proteins in PvAPs from P5 to P60. Furthermore, we found that distribution of mRNAs in PvAPs is perturbed in a mouse model of megalencephalic leukoencephalopathy with subcortical cysts. Lastly, we found that some polysomal mRNAs polarized progressively towards the PvAPs. Our results indicate that dynamic mRNA distribution and local translation influence the postnatal maturation of PvAPs. Summary statementLocal translation operates during the postnatal development of perivascular astrocyte processes and might contribute to their molecular maturation.