TABLE 1.

Summary of kidney phenotypes in mice with mutations or knockouts of core PCP protein-encoding genes.

Gene	Function in PCP and localisation in kidney	Phenotype in mutant or knockout kidneys	Evidence for PCP in these contexts
Celsr	Encodes a family of seven-pass transmembrane proteins localised on membranes on the opposite side of planar-polarised cells to FZD. Permits exchange of polarity information between cells. Celsr1-3 expressed on ureteric bud epithelium at E14.5 (Shima et al., 2002). Celsr1 expressed by S-shaped bodies, podocytes, and proximal tubular epithelium at E18.5 (Yates et al., 2010)	Celsr1Crsh/+; Vangl2Lp/+: more rudimentary ureteric trees than single heterozygotes defects and more prominent in caudal region, tubular dilations not observed, immature glomeruli (Brzóska et al., 2016) Celsr1Crsh/Crsh: reduced ureteric bud tip number more prominently in caudal portion of the kidney, cortical tubular dilation, no glomerular phenotype (Brzóska et al., 2016)	Deviation of axis of mitotic spindles in tubular epithelial cells in Celsr1Crsh/Crsh mice relative to longitudinal axis of tubule (Brzóska et al., 2016), suggestive of defective orientation of cell division. Phenotypes from double heterozygous Celsr1Crsh/+; Vangl2Lp/+ animals (Brzóska et al., 2016) suggest these components interact and potentially affect the same biological processes. Other planar-polarised behaviours or asymmetric expression of CELSR1 not reported during ureteric bud branching or glomerular morphogenesis
Fzd	Encodes G protein-coupled receptors which accumulate on opposite side of cell membrane to VANGL/CELSR in planar-polarised cells. Respond to WNT ligands to align planar-polarised tissues. FZD3 and FZD6 expressed by proximal tubular and collecting duct epithelial cells at E18.5 (Kunimoto et al., 2017)	Fzd3–/–; Fzd6–/–: dilation of proximal tubules and collecting ducts (Kunimoto et al., 2017) Fzd4–/–; Fzd8–/–: reduced ureteric bud tip number (Ye et al., 2011)	FZD3 and FZD6 asymmetrically distributed on the distal side of proximal tubular and collecting duct epithelial cells (Kunimoto et al., 2017). Asymmetric distribution of FZD4 and FZD8 not ascertained. Increased number of epithelial cells in cross-sections of proximal tubules and collecting ducts of Fzd3–/–;Fzd6–/– embryonic kidneys (Kunimoto et al., 2017)
Vangl	Encodes proteins with four transmembrane domains which accumulate on the opposite side of cell membrane to FZD in planar-polarised cells. Permits exchange of polarity information between cells. VANGL1 and VANGL2 expressed by collecting duct epithelial cells at E18.5 (Kunimoto et al., 2017) and VANGL2 expressed by developing podocytes at E17.5 (Rocque et al., 2015).	Vangl2Lp/Lp: reduced ureteric bud tip number, immature glomeruli, proximal tubular, and collecting duct dilation (Yates et al., 2010; Kunimoto et al., 2017; Derish et al., 2020)	VANGL1 and VANGL2 asymmetrically localised on collecting duct epithelial cell membranes (Kunimoto et al., 2017) but asymmetry not clearly demonstrated in podocytes. Increased number of epithelial cells in cross-sections of proximal tubules or collecting ducts of Vangl2Lp/Lp (Kunimoto et al., 2017; Derish et al., 2020), Vangl2ΔEx4/ΔEx4 and Hoxb7-Cre;Vangl2ΔEx4/fl (Derish et al., 2020) embryonic kidneys. Changes in mitotic orientation not examined in the context of reduced podocyte number.
		Vangl2ΔEx4/ΔEx4*: dilation of collecting ducts (Derish et al., 2020)
		Celsr1Crsh/+; Vangl2Lp/+: as above (Brzóska et al., 2016)
		Ksp-Cre;Vangl1fl/fl;Vangl2fl/fl: dilation of collecting ducts (Kunimoto et al., 2017)
		Hoxb7-Cre;Vangl2ΔEx4/fl *: dilation of collecting ducts (Derish et al., 2020)
		Nphs2-Cre:Vangl2ΔEx4/fl *: immature glomeruli and reduced podocyte (Rocque et al., 2015)
		Nphs2-Cre:Vangl2fl/fl: immature glomeruli (Papakrivopoulou et al., 2018)

^∗Vangl2 ^ΔEx4 allele generated by crossing Vangl2^fl/fl mouse with MORE-Cre to delete exon 4 of Vangl2 in all epiblast cells.