Pals1 Haploinsufficiency Results in Proteinuria and Cyst Formation

Abstract

The nephron is the basic physiologic subunit of the mammalian kidney and is made up of several apicobasally polarized epithelial cell types. The process of apicobasal polarization in animal cells is controlled by the evolutionarily conserved Crumbs (CRB), Partitioning-defective, and Scribble protein complexes. Here, we investigated the role of protein associated with LIN-7 1 (Pals1, also known as Mpp5), a core component of the apical membrane-determining CRB complex in the nephron. Pals1 interacting proteins, including Crb3 and Wwtr1/Taz, have been linked to renal cyst formation in mice before. Immunohistologic analysis revealed Pals1 expression in renal tubular cells and podocytes of human kidneys. Mice lacking one Pals1 allele (functionally haploid for Pals1) in nephrons developed a fully penetrant phenotype, characterized by cyst formation and severe defects in renal barrier function, which led to death within 6-8 weeks. In nephrocytes, deficiency of the Pals1 ortholog caused alterations in slit-diaphragm-like structures. Additional studies in epithelial cell culture models revealed that Pals1 functions as a dose-dependent upstream regulator of the crosstalk between Hippo- and TGF--mediated signaling. Furthermore, Pals1 haploinsufficiency in mouse kidneys associated with the upregulation of Hippo pathway target genes and marker genes of TGF- signaling, including biomarkers of renal diseases. These findings support a link between apical polarity proteins and renal diseases, especially renal cyst diseases. Further investigation of the Pals1-linked networks is required to decipher the mechanisms underlying the pathogenesis of these diseases.

Allele-specific RNA imaging shows that allelic imbalances can arise in tissues through transcriptional bursting

“…while a cell may have mRNA from only one allele at a particular time, it may gain mRNA from the other allele a short time later if another transcriptional event occurs. For Mpp5 , this conclusion is in line with the fact that the reported haploinsufficient phenotype is thought to be caused by overall reduced dosage(Straight et al 2004;Weide et al 2017) rather than by a special subpopulation of cells with monoallelic expression. More generally, this scenario links the observation of transcriptional bursting with that of random monoallelic expression, as put forward by Sandberg et al(Reinius and Sandberg 2015;Reinius et al 2016) , and explains why we (and others previously(Gendrel et al 2014; ) observed the co-occurrence of cells with one and two transcription sites in the same population.…”

“…These genes were selected to represent genes with ( Aebp1 , Churc1 , Lyplal1 ) and without ( Aqp11 , Mpp5 , Podxl, Prcp, Stard5 ) putative random monoallelic expression (Gendrel et al 2014;Li et al 2012;Zwemer et al 2012) and with different expression levels, patterns and chromosomal locations. Some of the chosen genes were also linked to specific kidney disease phenotypes ( Aqp11 (Ishibashi, Hara, and Kondo 2009) , Mpp5 (Straight et al 2004;Weide et al 2017) , Prcp (Maier et al 2017) ) ( Table S4). As expected, these genes were typically expressed at much lower levels than Xist and punctate individual mRNA spots could not be as readily observed in low magnification scans.…”

Allele-specific RNA imaging shows that allelic imbalances can arise in tissues through transcriptional bursting

“…These genes were selected to represent genes with ( Aebp1 , Churc1 , Lyplal1 ) and without ( Aqp11 , Mpp5 , Podxl , Prcp , Stard5 ) putative random monoallelic expression [38–41] and with different expression levels, patterns and chromosomal locations. Some of the chosen genes were also linked to specific kidney disease phenotypes ( Aqp11 [54], Mpp5 [55,56], Prcp [57] ) (Methods, S4 Table). As expected, these genes were typically expressed at much lower levels than Xist and punctate individual mRNA spots could not be as readily observed in low magnification scans.…”

Three-dimensional architecture of pericardial nephrocytes in Drosophila melanogaster revealed by FIB/SEM tomography

“…1h). The molecular components of the slit diaphragm are highly conserved between the nephrocytes in D. melanogaster and podocytes in vertebrates (Weavers et al 2009;Zhuang et al 2009) and Drosophila nephrocytes have recently been used as a model system to study podocyte function and disease (Fu et al 2017;Helmstädter and Simons 2017;Na et al 2015;Tutor et al 2014;Weide et al 2017). Podocytes are localized at the glomerulus (G), a primary urine-producing apparatus.…”