Disruption of Mks1 localization to the mother centriole causes cilia defects and developmental malformations in Meckel-Gruber syndrome

Abstract

SUMMARYMeckel-Gruber syndrome (MKS) is a recessive disorder resulting in multiple birth defects that are associated with mutations affecting ciliogenesis. We recovered a mouse mutant with a mutation in the Mks1 gene (Mks1del64-323) that caused a 260-amino-acid deletion spanning nine amino acids in the B9 domain, a protein motif with unknown function conserved in two other basal body proteins. We showed that, in wild-type cells, Mks1 was localized to the mother centriole from which the cilium was generated. However, in mutant Mks1del64-323 cells, Mks1 was not localized to the centriole, even though it maintained a punctate distribution. Resembling MKS patients, Mks1 mutants had craniofacial defects, polydactyly, congenital heart defects, polycystic kidneys and randomized left-right patterning. These defects reflected disturbance of functions subserved by motile and non-motile cilia. In the kidney, glomerular and tubule cysts were observed along with short cilia, and cilia were reduced in number to a near-complete loss. Underlying the left-right patterning defects were fewer and shorter nodal cilia, and analysis with fluorescent beads showed no directional flow at the embryonic node. In the cochlea, the stereocilia were mal-patterned, with the kinocilia being abnormally positioned. Together, these defects suggested disruption of planar cell polarity, which is known to regulate node, kidney and cochlea development. In addition, we also showed that Shh signaling was disrupted. Thus, in the neural tube, the floor plate was not specified posteriorly even as expression of the Shh mediator Gli2 increased. By contrast, the Shh signaling domain was expanded in the anterior neural tube and anterior limb bud, consistent with reduced Gli3-repressor (Gli3R) function. The latter probably accounted for the preaxial digit duplication exhibited by the Mks1del64-323 mutants. Overall, these findings indicate that centriole localization of Mks1 is required for ciliogenesis of motile and non-motile cilia, but not for centriole assembly. On the basis of these results, we hypothesize a role for the B9 domain in mother centriole targeting, a possibility that warrants further future investigations.

The Meckel syndrome- associated protein MKS1 functionally interacts with components of the BBSome and IFT complexes to mediate ciliary trafficking and hedgehog signaling

“…Bbs4 -/- mutant embryos exhibit normal neural patterning (Fig 1J). Previous studies examining the phenotypes of Mks1 mutant embryos report complex neural patterning phenotypes wherein cell types that require intermediate levels of SHH for their patterning are slightly expanded, with the ventral most cells including V3 interneurons slightly reduced in number in more caudal regions of the neural tube [39,48]. We similarly observed only a slight expansion of OLIG2+ motor neuron progenitors at the forelimb level in Mks1 single mutants (Fig 1K).…”

Wdpcp, a PCP Protein Required for Ciliogenesis, Regulates Directional Cell Migration and Cell Polarity by Direct Modulation of the Actin Cytoskeleton

“…Particularly notable is their phenotypic similarity to Mks1 mutant mice that are models of MKS [27],[28]. This included anophthalmia (Figure 1A), central polydactyly (Figure 1B,C), and cysts in the kidney and a variety of other organs (Figure 1D,E).…”

The old and new face of craniofacial research: How animal models inform human craniofacial genetic and clinical data

“…For example, two independent studies identified recessive mutations in Mks1, and showed that loss of this gene impacted the assembly of functional cilia. Moreover, these mouse mutants had phenotypes similar to those seen in human Meckel Syndrome, Type 1 (Cui et al, 2011; Norris and Grimes, 2012; Weatherbee et al, 2009), including craniofacial defects, and the mutation in the Mks1 krc allele was also detected at an equivalent position in MKS1 for an affected human patient (Norris and Grimes, 2012). Similarly, the ENU-induced Cauli phenotype, which results in missing or reduced facial cartilage and bone among other defects, is caused by a mutation in Ift40 (Miller et al, 2013).…”