Spatiotemporal dynamics of mTORC1 and mTORC2 in the developing spinal cord and their essential roles in gliogenesis.

Abstract

Background: Mechanistic target of rapamycin (mTOR) is a serine/threonine kinase with diverse roles in development and homeostasis, but its spatiotemporal dynamics in the embryonic spinal cord are not fully defined. Here, we map mTOR activity across mouse spinal cord development and test its function using a conditional gene mutant.

Results: Immunohistochemistry for phosphorylated readouts of mTORC1 and mTORC2 revealed distinct, stage-dependent patterns. In the early neural tube, phosphorylated S6 (p-S6; Ser235/236 and Ser240/244) marked dorsal progenitors and ventral motor neurons, while p-p70S6K, p-4E-BP1, and p-Akt (Ser473) were enriched along the luminal surface where mitoses occur. By E13.5, p-S6 persisted in the motor column, whereas p-p70S6K, p-4E-BP1, and luminal p-Akt remained ventricular; at E18.5, robust p-S6 and p-p70S6K signals were localized to neuronal somata and fibers in the marginal layer, with minimal p-Akt. Closer examination revealed that mTORC1/2 signals preferentially colocalized with pHH3-positive ventricular progenitors early, then decoupled as development progressed. Within motor neurons, mTORC1 broadly overlapped with Islet1, including the Lhx3-positive medial motor column (MMC), whereas mTORC2 (p-Akt) labeled an Islet1-positive subset complementary to Lhx3 and declined over time, demarcating lateral, non-MMC domains. Nestin-Cre-mediated mTOR deletion did not overtly affect neuronal organization but reduced GFAP- and Sox10-positive glial lineage cells, indicating a selective requirement of mTOR for glial differentiation.

Conclusions: Together, the data suggest separable and temporal roles of mTORC1 and mTORC2 in progenitor mitosis, motor-neuron domain organization, and late embryonic gliogenesis.