Decoding Cortical Glial Cell Development

Mouse cortical radial glial cells(RGCs)are primary neural stem cells that give rise to cortical oligodendrocytes,astrocytes,and olfactory bulb(OB)GABAergic interneurons in late embryogenesis.There are fundamental gaps in understanding how these diverse cell subtypes are generated.Here,by combining single-cell RNA-Seq with intersectional lineage analyses,we show that beginning at around E16.5,neocortical RGCs start to generate ASCL1^(+)EGFR^(+)apical multipotent intermediate progenitors(MIPCs),which then differentiate into basal MIPCs that express ASCL1,EGFR,OLIG2,and MKI67.These basal MIPCs undergo several rounds of divisions to generate most of the cortical oligodendrocytes and astrocytes and a subpopulation of OB interneurons.Finally,single-cell ATAC-Seq supported our model for the genetic logic underlying the specification and differentiation of cortical glial cells and OB interneurons.Taken together,this work reveals the process of cortical radial glial cell lineage progression and the developmental origins of cortical astrocytes and oligodendrocytes.

Homeobox Gene Six3 is Required for the Differentiation of D2-Type Medium Spiny Neurons

Medium spiny neurons(MSNs)in the striatum,which can be divided into D1 and D2 MSNs,originate from the lateral ganglionic eminence(LGE).Previously,we reported that Six3 is a downstream target of Sp8/Sp9 in the transcriptional regulatory cascade of D2 MSN development and that conditionally knocking out Six3 leads to a severe loss of D2 MSNs.Here,we showed that Six3 mainly functions in D2 MSN precursor cells and gradually loses its function as D2 MSNs mature.Conditional deletion of Six3 had little effect on cell proliferation but blocked the differentiation of D2 MSN precursor cells.In addition,conditional overexpression of Six3 promoted the differentiation of precursor cells in the LGE.We measured an increase of apoptosis in the postnatal striatum of conditional Six3-knockout mice.This suggests that,in the absence of Six3,abnormally differentiated D2 MSNs are eliminated by programmed cell death.These results further identify Six3 as an important regulatory element during D2 MSN differentiation.