MEIS-WNT5A axis regulates development of fourth ventricle choroid plexus

Abstract

The choroid plexus (ChP) produces cerebrospinal fluid and forms an essential brain barrier. ChP tissues form in each brain ventricle, each one adopting a distinct shape, but remarkably little is known about the mechanisms underlying ChP development. Here, we show that epithelial WNT5A is crucial for determining fourth ventricle (4V) ChP morphogenesis and size in mouse. Systemic Wnt5a knockout, or forced Wnt5a overexpression beginning at embryonic day 10.5, profoundly reduced ChP size and development. However, Wnt5a expression was enriched in Foxj1-positive epithelial cells of 4V ChP plexus, and its conditional deletion in these cells affected the branched, villous morphology of the 4V ChP. We found that WNT5A was enriched in epithelial cells localized to the distal tips of 4V ChP villi, where WNT5A acted locally to activate non-canonical WNT signaling via ROR1 and ROR2 receptors. During 4V ChP development, MEIS1 bound to the proximal Wnt5a promoter, and gain- and loss-of-function approaches demonstrated that MEIS1 regulated Wnt5a expression. Collectively, our findings demonstrate a dual function of WNT5A in ChP development and identify MEIS transcription factors as upstream regulators of Wnt5a in the 4V ChP epithelium.

Experimental approaches for manipulating choroid plexus epithelial cells

“…Consistent with this idea, the epithelial cells at the tips of the villi of the 3V and 4V ChP that are bathed by the CSF show higher rates of transduction, compared to epithelial cells at the base of the villi (see Supp Fig. 7D in [ 53 ]). While I.C.V.…”

“…However, due to findings that Wnt1-Cre transgenic mice show ectopic upregulation of Wnt1 expression and unintended midbrain phenotypes, a newer, Wnt1-Cre2 has been generated [ 52 ]. This new Wnt1-Cre2 line has been used to delete Meis1 in 4V ChP in a Meis1 fl/fl line [ 53 ]. Other cases of a 4V ChP conditional knockout of Sox9 can be achieved with Pax2-Cre mice [ 19 ].…”

“…Upon tamoxifen binding, Cre translocates to the nucleus where it catalyzes recombination [ 65 ]. In the ChP, the mouse Foxj1 promoter-driven Cre ERT2 system ( Foxj1 CreERT2::GFP ) [ 66 ] induced by tamoxifen at E10.5-E12.5 can be used for conditional ablation of gene expression during the early stages of ChP development, as was done with Wnt5a in 4V ChP epithelial cells [ 53 , 67 ], resulting in altered morphogenesis of 4V ChP. To elucidate the critical role of transcription factor Otx2 in the development and maintenance of the ChP, Otx2-Cre ERT2 mice were generated by replacing the genomic region spanning the Otx2 coding sequence, and then crossed with Otx2 fl/fl mice [ 68 , 69 ].…”

“…c P0 or P1 No Yes 4 weeks [ 116 ] 4–8 weeks No Yes 4 weeks [ 116 ] 6–8 weeks Not tested Yes 4 weeks [ 155 ] 85 days Yes Yes Up to 160 days [ 156 ] AAV2/5 I.C.V. c E10.5 Yes Not tested E16.5 [ 53 ] E13.5 Yes No E15.5 [ 87 ] E13.5 Yes No Up to E18.5 [ 53 ] E14.5 Yes Not tested P18-P24 [ 38 ] E15 Yes No 130 days [ 88 ] P0.5 b Yes Yes Up to 15 months [ 92 ] P2-P3 ...…”

“…Inset (dashed line box) highlights detection of AAV2/5-GFP and AQP1 expression in the ChP epithelium. Experiment conducted as in [ 53 ] …”