Dephosphorylation of 4EBP1/2 Induces Prenatal Neural Stem Cell Quiescence

Abstract

A limiting factor in the regenerative capacity of the adult brain is the abundance and proliferative ability of neural stem cells (NSCs). Adult NSCs are derived from a subpopulation of embryonic NSCs that temporarily enter quiescence during mid-gestation and remain quiescent until postnatal reactivation. Here we present evidence that the mechanistic/mammalian target of rapamycin (mTOR) pathway regulates quiescence entry in embryonic NSCs of the developing forebrain. Throughout embryogenesis, two downstream effectors of mTOR, p-4EBP1/2 T37/46 and p-S6 S240/244, were mutually exclusive in NSCs, rarely occurring in the same cell. While 4EBP1/2 was phosphorylated in stem cells undergoing mitosis at the ventricular surface, S6 was phosphorylated in more differentiated cells migrating away from the ventricle. Phosphorylation of 4EBP1/2, but not S6, was responsive to quiescence induction in cultured embryonic NSCs. Further, inhibition of p-4EBP1/2, but not p-S6, was sufficient to induce quiescence. Collectively, this work offers new insight into the regulation of quiescence entry in embryonic NSCs and, thereby, correct patterning of the adult brain. These data suggest unique biological functions of specific posttranslational modifications and indicate that the preferential inhibition of such modifications may be a useful therapeutic approach in neurodevelopmental diseases where NSC numbers, proliferation, and differentiation are altered.

Single Cell Profiling Distinguishes Leukemia-Selective Chemotypes

“…To investigate whether rocaglates from different structural subgroups were bioactive in MV411 leukemia cells and whether this bioactivity extended to healthy cells, we tested an expanded library of 37 rocaglates, intentionally weighted toward known bioactive molecules, with representation from each of the three subclasses at 10 µM on MV411 and healthy peripheral blood mononuclear cells (PBMCs) (Figure 2A). The primary staining panel was selected to test a range of cell functions including cell growth, translation, and death and has been validated in previous work: Ki67 (cell proliferation 45,46 ), phospho-S6 ribosomal protein at serine 240/244 (p-S6 S240/244) (growth, AKT/mTORC1 specific 47,48 ), phosphorylation of gamma H2AX at serine 139 (γH2AX) (DNA damage response 49 ), phosphorylation of STAT3 at serine 727 (p-STAT3) (amplified transcriptional activity, downstream mTOR 50 ), phosphorylation of STAT5 at tyrosine 694 (p-STAT5) (cell survival, highly phosphorylated in cancer cells 51,52 ), phospho-S6 ribosomal protein at serine 235/236 (p-S6 235/236) (growth, activated by ERK/RSK and AKT/mTORC1 47,48 ), phosphorylation of ERK1/ERK2 at threonine 202, tyrosine 204 (p-ERK1/2) (proliferation, activated by MAP kinase cascade 53,54 ), phosphorylated histone H3 at serine 28 (p-HH3) (growth, cell cycle M phase 55 ), phosphorylation of 4EBP1 at threonine 37/46 (p-4EBP1) (growth, activated by mTORC1 56 ), phosphorylation of lymphocyte-specific protein tyrosine kinase at tyrosine 505 (p-LCK) (SRC-family kinase involved in T-cell receptor signaling 57 ), and phosphorylation of Akt at serine 473 (p-Akt) (Upstream of mTOR 41,58 ) (Supplementary Table 1) 59,44,60 .…”

Multiscale modeling uncovers 7q11.23 copy number variation–dependent changes in ribosomal biogenesis and neuronal maturation and excitability

“…The uncoupling of p-4EBP and p-RPS6 has already been documented in neurogenesis. For example, while p-4EBP marks neural stem cells undergoing mitosis and NPCs at the ventricular surface, p-RPS6 marks more differentiated cells migrating away from the ventricle ( 9 , 42 , 43 ). Interestingly, it was shown that NPCs marked with p-4EBP had higher levels of ribosomal protein mRNAs compared with more mature neurons marked with p-RPS6, but the difference was buffered at the level of translation in cortical brain organoids ( 43 ).…”