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

Cui C, Chatterjee B, Francis D, Yu Q, SanAgustin JT, Francis R, Tansey T, Henry C, Wang B, Lemley B, Pazour GJ, Lo CW - Dis Model Mech (2010)

Bottom Line: Meckel-Gruber syndrome (MKS) is a recessive disorder resulting in multiple birth defects that are associated with mutations affecting ciliogenesis.By contrast, the Shh signaling domain was expanded in the anterior neural tube and anterior limb bud, consistent with reduced Gli3-repressor (Gli3R) function.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.

View Article: PubMed Central - PubMed

Affiliation: University of Pittsburgh, Department of Developmental Biology, 8111 Rangos Research Center, 530 45th Street, Pittsburgh, PA 15201, USA.

ABSTRACT
Meckel-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 (Mks1(del64-323)) 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 Mks1(del64-323) 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 Mks1(del64-323) 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.

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Scanning EM shows defects in patterning of cochlear hair cells in Mks1 mutants. In newborn wild-type (ctrl) cochlea (A), three rows of OHCs were aligned in parallel rows (arrows in A) but, in the Mks1 mutant animal (m/m; B), some OHCs were mal-positioned, with abnormal orientation of the stereocilia hair bundles. Higher magnification (C–F) showed that kinocilia (black arrows) in mutant hair cells (D–F) were of normal length compared to controls (C), but they were abnormally localized relative to the stereocilia hair bundles.
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f7-0040043: Scanning EM shows defects in patterning of cochlear hair cells in Mks1 mutants. In newborn wild-type (ctrl) cochlea (A), three rows of OHCs were aligned in parallel rows (arrows in A) but, in the Mks1 mutant animal (m/m; B), some OHCs were mal-positioned, with abnormal orientation of the stereocilia hair bundles. Higher magnification (C–F) showed that kinocilia (black arrows) in mutant hair cells (D–F) were of normal length compared to controls (C), but they were abnormally localized relative to the stereocilia hair bundles.

Mentions: We examined the formation of specialized cilia in the developing cochlea that are known as the kinocilia. Kinocilia play a crucial role in the patterning of actin-based microvilli, which are referred to as stereocilia, a process that is regulated by cilia-transduced PCP signaling (Jones et al., 2008; Kelly and Chen, 2007). In the cochlea, there are normally three outer rows [outer hair cells (OHCs)] and one inner row [inner hair cells (IHCs)] of hair cells, and, in each hair cell, a kinocilium is positioned at the tip of the ‘chevron’-shaped stereocilia bundles (Fig. 7A). In the Mks1-mutant cochlea, although the kinocilia were present and seemed to be of normal length and morphology, they were often misplaced relative to the stereocilia bundles (Fig. 7D–F). Thus, sometimes they were found adjacent to or within the stereocilia bundles (Fig. 7D), displaced to one side of the stereocilia bundles (Fig. 7F) or encircled by a stereocilia bundle ring (Fig. 7E).


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

Cui C, Chatterjee B, Francis D, Yu Q, SanAgustin JT, Francis R, Tansey T, Henry C, Wang B, Lemley B, Pazour GJ, Lo CW - Dis Model Mech (2010)

Scanning EM shows defects in patterning of cochlear hair cells in Mks1 mutants. In newborn wild-type (ctrl) cochlea (A), three rows of OHCs were aligned in parallel rows (arrows in A) but, in the Mks1 mutant animal (m/m; B), some OHCs were mal-positioned, with abnormal orientation of the stereocilia hair bundles. Higher magnification (C–F) showed that kinocilia (black arrows) in mutant hair cells (D–F) were of normal length compared to controls (C), but they were abnormally localized relative to the stereocilia hair bundles.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3008963&req=5

f7-0040043: Scanning EM shows defects in patterning of cochlear hair cells in Mks1 mutants. In newborn wild-type (ctrl) cochlea (A), three rows of OHCs were aligned in parallel rows (arrows in A) but, in the Mks1 mutant animal (m/m; B), some OHCs were mal-positioned, with abnormal orientation of the stereocilia hair bundles. Higher magnification (C–F) showed that kinocilia (black arrows) in mutant hair cells (D–F) were of normal length compared to controls (C), but they were abnormally localized relative to the stereocilia hair bundles.
Mentions: We examined the formation of specialized cilia in the developing cochlea that are known as the kinocilia. Kinocilia play a crucial role in the patterning of actin-based microvilli, which are referred to as stereocilia, a process that is regulated by cilia-transduced PCP signaling (Jones et al., 2008; Kelly and Chen, 2007). In the cochlea, there are normally three outer rows [outer hair cells (OHCs)] and one inner row [inner hair cells (IHCs)] of hair cells, and, in each hair cell, a kinocilium is positioned at the tip of the ‘chevron’-shaped stereocilia bundles (Fig. 7A). In the Mks1-mutant cochlea, although the kinocilia were present and seemed to be of normal length and morphology, they were often misplaced relative to the stereocilia bundles (Fig. 7D–F). Thus, sometimes they were found adjacent to or within the stereocilia bundles (Fig. 7D), displaced to one side of the stereocilia bundles (Fig. 7F) or encircled by a stereocilia bundle ring (Fig. 7E).

Bottom Line: Meckel-Gruber syndrome (MKS) is a recessive disorder resulting in multiple birth defects that are associated with mutations affecting ciliogenesis.By contrast, the Shh signaling domain was expanded in the anterior neural tube and anterior limb bud, consistent with reduced Gli3-repressor (Gli3R) function.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.

View Article: PubMed Central - PubMed

Affiliation: University of Pittsburgh, Department of Developmental Biology, 8111 Rangos Research Center, 530 45th Street, Pittsburgh, PA 15201, USA.

ABSTRACT
Meckel-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 (Mks1(del64-323)) 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 Mks1(del64-323) 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 Mks1(del64-323) 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.

Show MeSH
Related in: MedlinePlus