CCND1 and neoplasm: Further, although the slightly elevated WNT activity in LRP4 mutants was not sufficient to increase the average Cyclin D1 levels and mitotic activity in the forebrain neuroepithelium (Figures 4, 6), the observed sporadic locally appearing over-proliferative tumour-like neuroepithelial domains might be caused by increased canonical WNT signalling in LRP4 loss-of-function mutants (Supplementary Figures S4, S5).