Wnt signaling mutants have decreased dentate granule cell production and radial glial scaffolding abnormalities

Abstract

LRP6 mutant mice have generalized defects in the Wnt/beta-catenin signaling pathway because of the crucial function of LRP6 as a Wnt signaling co-receptor (Pinson et al., 2000). We examined the hippocampal phenotype of single LRP6 mutant mice as well as LRP6/Lef1 double mutant mice. LRP6 mutants had reduced production of dentate granule neurons and abnormalities of the radial glial scaffolding in the forming dentate gyrus. These defects were more severe with the addition of a single Lef1 null allele to an LRP6 null background. Pyramidal cell fields were unaffected in the LRP6, Lef1, or double mutants. The dentate defects were accompanied by decreased numbers of mitotic precursors in the migratory pathway to the dentate and in the displaced proliferative zone in the dentate itself. At earlier gestational ages, there was a reduction in the number of dentate granule cell progenitors in the dentate ventricular zone before the emigration of the earliest differentiated granule neurons and precursors to form the dentate anlage.

Figure 1.

Hippocampal organization in LRP6 mutants at E18.5. Coronal sections from wild-type mice (A-F) and LRP6-/- mice (A′-F′) were stained using antibodies or by in situ hybridization. In some panels, dotted black lines outline the dentate gyrus. Fi, Fimbria; Sub, subiculum; DG, dentate gyrus.

Figure 2.

Loss of differentiated granule and precursor cells in E18.5 mutant mice. A-E are stained with antibody to Prox1, A′-E′ are stained with antibody to BrdU, and A″-E″ are the overlaid images. The outlines of the migratory route and dentate gyrus are indicated by the dotted line in each panel. In A′, the arrow indicates the width of the migratory pathway. F shows a graph of the counting data for cell types in each compartment. Error bars are SEM, and each data point is based on at least three animals of for each genotype. LV, Lateral ventricle; dgv, dentate gyrus ventricular zone; dgm, dentate gyrus migratory route; DG, dentate gyrus; Fi, fimbria.

Figure 3.

Radial glial scaffolding in Wnt signaling mutants. GFAP antibody staining of coronal sections at E17.5. Arrows indicate the proper position of the dentate anlage. Note that mutants lack the radial glial scaffolding in the mutants of all genotypes. LV, Lateral ventricle; DG, dentate gyrus; Fi, fimbria; VZ, ventricular zone.

Figure 4.

The ventricular zone region containing dentate precursors at mid-gestation (E13.5) is reduced in LRP6 mutants. A and B show Prox1/TuJ1/DNA triple-labeling. TuJ1 is a mouse monoclonal specific for a neuronal form of β-tubulin that is expressed in the cortical plate. The dotted line indicates the region of Prox1 staining in the ventricular zone that is concentrated above the cortical hem. C and D show Prox1/BrdU double-labeling. In the dentate ventricular zone, all the BrdU-labeled cells in the ventricular zone express Prox1. E shows the counting data for BrdU/Prox1 double-labeled cells.