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Atypical protein kinase C controls sea urchin ciliogenesis.

Prulière G, Cosson J, Chevalier S, Sardet C, Chenevert J - Mol. Biol. Cell (2011)

Bottom Line: We found that in the early embryo aPKC is uniformly cortical and becomes excluded from the vegetal pole during unequal cleavages at the 8- to 64-cell stages.A dose-dependent and reversible inhibition of aPKC results in mislocalization of the kinase, defective ciliogenesis, and lack of swimming.Thus, as in the primary cilium of differentiated mammalian cells, aPKC controls the growth of motile cilia in invertebrate embryos.

View Article: PubMed Central - PubMed

Affiliation: Observatoire Océanologique, Biologie du Développement, Université Pierre et Marie Curie and CNRS, Villefranche-sur-Mer, France. pruliere@obs-vlfr.fr

ABSTRACT
The atypical protein kinase C (aPKC) is part of the conserved aPKC/PAR6/PAR3 protein complex, which regulates many cell polarity events, including the formation of a primary cilium at the apical surface of epithelial cells. Cilia are highly organized, conserved, microtubule-based structures involved in motility, sensory processes, signaling, and cell polarity. We examined the distribution and function of aPKC in the sea urchin embryo, which forms a swimming blastula covered with motile cilia. We found that in the early embryo aPKC is uniformly cortical and becomes excluded from the vegetal pole during unequal cleavages at the 8- to 64-cell stages. During the blastula and gastrula stages the kinase localizes at the base of cilia, forming a ring at the transition zone between the basal body and the elongating axoneme. A dose-dependent and reversible inhibition of aPKC results in mislocalization of the kinase, defective ciliogenesis, and lack of swimming. Thus, as in the primary cilium of differentiated mammalian cells, aPKC controls the growth of motile cilia in invertebrate embryos. We suggest that aPKC might function to phosphorylate kinesin and so activate the transport of intraflagellar vesicles.

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Related in: MedlinePlus

Schematic representation of sea urchin embryonic development. The times in blue indicate hours postfertilization. The sea urchin oocyte is organized along an animal–vegetal (A/V) primary axis, which is observable in P. lividus due to the presence of a subequatorial cortical pigmented band visible under blue light (arrow in A). Fertilization is followed by first and second cleavages, which are meridional (parallel to the A/V axis) and perpendicular to each other (B, C). The third cleavage is equatorial, perpendicular to the first two cleavage planes, and separates the animal and vegetal hemispheres from one another (D). During the fourth cleavage, animal blastomeres divide equally to produce eight mesomeres, and the vegetal blastomeres divide unequally to produce large macromeres and small micromeres located at the vegetal pole of the embryo (E, F). Six hours after fertilization the sea urchin embryo enters the early blastula stage with an empty central cavity called a blastocoel (G). The cells start developing cilia on their outer surface to form a swimming blastula (H). Approximately 10–12 h after fertilization, the midblastula, composed of ∼600 cells, hatches out of the fertilization envelope (not shown). At the animal pole, the cilia are longer but do not beat. This “apical tuft” (I) provides directionality to swimming, as embryos almost always move with the apical tuft region forward. In the late blastula stage the embryo becomes thickened at the vegetal pole, forming the vegetal plate (I). This represents the gastrulation site where the primary mesenchyme cells (PMCs), which are derived from the micromeres and located in the center of the vegetal plate region, migrate into the blastocoel (I, J). The vegetal cells will continue to ingress in order to form the archenteron, led by filopodia extending from the secondary mesenchyme cells (SMCs), which eventually contact the animal pole at the future site of mouth formation (K). A prism (not shown) and finally a feeding pluteic larva will be formed 24 h later around an endoskeleton, which contains two spicules made of calcium carbonate secreted by the PMCs (L). A few days later, this pluteus will metamorphose into a tiny male or female adult urchin.
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Figure 1: Schematic representation of sea urchin embryonic development. The times in blue indicate hours postfertilization. The sea urchin oocyte is organized along an animal–vegetal (A/V) primary axis, which is observable in P. lividus due to the presence of a subequatorial cortical pigmented band visible under blue light (arrow in A). Fertilization is followed by first and second cleavages, which are meridional (parallel to the A/V axis) and perpendicular to each other (B, C). The third cleavage is equatorial, perpendicular to the first two cleavage planes, and separates the animal and vegetal hemispheres from one another (D). During the fourth cleavage, animal blastomeres divide equally to produce eight mesomeres, and the vegetal blastomeres divide unequally to produce large macromeres and small micromeres located at the vegetal pole of the embryo (E, F). Six hours after fertilization the sea urchin embryo enters the early blastula stage with an empty central cavity called a blastocoel (G). The cells start developing cilia on their outer surface to form a swimming blastula (H). Approximately 10–12 h after fertilization, the midblastula, composed of ∼600 cells, hatches out of the fertilization envelope (not shown). At the animal pole, the cilia are longer but do not beat. This “apical tuft” (I) provides directionality to swimming, as embryos almost always move with the apical tuft region forward. In the late blastula stage the embryo becomes thickened at the vegetal pole, forming the vegetal plate (I). This represents the gastrulation site where the primary mesenchyme cells (PMCs), which are derived from the micromeres and located in the center of the vegetal plate region, migrate into the blastocoel (I, J). The vegetal cells will continue to ingress in order to form the archenteron, led by filopodia extending from the secondary mesenchyme cells (SMCs), which eventually contact the animal pole at the future site of mouth formation (K). A prism (not shown) and finally a feeding pluteic larva will be formed 24 h later around an endoskeleton, which contains two spicules made of calcium carbonate secreted by the PMCs (L). A few days later, this pluteus will metamorphose into a tiny male or female adult urchin.

Mentions: Ciliogenesis occurs during sea urchin embryo development immediately prior to hatching into a swimming blastula and it ensures embryo motility up to the feeding pluteic larva stage. After fertilization, a series of rapid cleavages gives rise to a blastoderm consisting of several hundred cells arranged as a spherical monolayer of epithelial cells surrounding the blastocoel (Figure 1, A–G). At this stage, each blastomere synthesizes during interphase one single motile cilium (Figure 1H), itself composed of an axoneme made of a scaffold of nine doublet and two singlet microtubules and several hundred additional proteins attached to a basal body (Dutcher, 1995; Dawe et al., 2007; Silverman and Leroux, 2009). In the sea urchin swimming embryo, as in other multicellular models, the cilia emanate from basal bodies situated right under the apical surface of blastula epithelial cells (Stephens, 2008). During mitosis, each cell retracts and disassembles its axoneme, builds a mitotic spindle with the centrioles as spindle poles, divides, and then returns its centriole pair to the apical cell surface to grow a new cilium (Masuda and Sato, 1984; Dawe et al., 2007). Ciliogenesis is linked to the animal–vegetal cell polarity in the sea urchin embryo. While the blastula starts gastrulating (Figure 1I), the vegetal blastomeres grow short and very active cilia, which follow a metachronic beating movement coordinated along the animal–vegetal axis to provide directional motility to the blastula and propel it in seawater (Stephens, 1995). On the animal side a small group of epithelial cells, which appear thicker than the vegetal cells, form longer and poorly active cilia, which protrude anteriorly to the embryo in an entangled way (Figure 1, I–K). This “apical tuft” plays the role of rudder, preventing random swimming (Stephens, 2008).


Atypical protein kinase C controls sea urchin ciliogenesis.

Prulière G, Cosson J, Chevalier S, Sardet C, Chenevert J - Mol. Biol. Cell (2011)

Schematic representation of sea urchin embryonic development. The times in blue indicate hours postfertilization. The sea urchin oocyte is organized along an animal–vegetal (A/V) primary axis, which is observable in P. lividus due to the presence of a subequatorial cortical pigmented band visible under blue light (arrow in A). Fertilization is followed by first and second cleavages, which are meridional (parallel to the A/V axis) and perpendicular to each other (B, C). The third cleavage is equatorial, perpendicular to the first two cleavage planes, and separates the animal and vegetal hemispheres from one another (D). During the fourth cleavage, animal blastomeres divide equally to produce eight mesomeres, and the vegetal blastomeres divide unequally to produce large macromeres and small micromeres located at the vegetal pole of the embryo (E, F). Six hours after fertilization the sea urchin embryo enters the early blastula stage with an empty central cavity called a blastocoel (G). The cells start developing cilia on their outer surface to form a swimming blastula (H). Approximately 10–12 h after fertilization, the midblastula, composed of ∼600 cells, hatches out of the fertilization envelope (not shown). At the animal pole, the cilia are longer but do not beat. This “apical tuft” (I) provides directionality to swimming, as embryos almost always move with the apical tuft region forward. In the late blastula stage the embryo becomes thickened at the vegetal pole, forming the vegetal plate (I). This represents the gastrulation site where the primary mesenchyme cells (PMCs), which are derived from the micromeres and located in the center of the vegetal plate region, migrate into the blastocoel (I, J). The vegetal cells will continue to ingress in order to form the archenteron, led by filopodia extending from the secondary mesenchyme cells (SMCs), which eventually contact the animal pole at the future site of mouth formation (K). A prism (not shown) and finally a feeding pluteic larva will be formed 24 h later around an endoskeleton, which contains two spicules made of calcium carbonate secreted by the PMCs (L). A few days later, this pluteus will metamorphose into a tiny male or female adult urchin.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3113769&req=5

Figure 1: Schematic representation of sea urchin embryonic development. The times in blue indicate hours postfertilization. The sea urchin oocyte is organized along an animal–vegetal (A/V) primary axis, which is observable in P. lividus due to the presence of a subequatorial cortical pigmented band visible under blue light (arrow in A). Fertilization is followed by first and second cleavages, which are meridional (parallel to the A/V axis) and perpendicular to each other (B, C). The third cleavage is equatorial, perpendicular to the first two cleavage planes, and separates the animal and vegetal hemispheres from one another (D). During the fourth cleavage, animal blastomeres divide equally to produce eight mesomeres, and the vegetal blastomeres divide unequally to produce large macromeres and small micromeres located at the vegetal pole of the embryo (E, F). Six hours after fertilization the sea urchin embryo enters the early blastula stage with an empty central cavity called a blastocoel (G). The cells start developing cilia on their outer surface to form a swimming blastula (H). Approximately 10–12 h after fertilization, the midblastula, composed of ∼600 cells, hatches out of the fertilization envelope (not shown). At the animal pole, the cilia are longer but do not beat. This “apical tuft” (I) provides directionality to swimming, as embryos almost always move with the apical tuft region forward. In the late blastula stage the embryo becomes thickened at the vegetal pole, forming the vegetal plate (I). This represents the gastrulation site where the primary mesenchyme cells (PMCs), which are derived from the micromeres and located in the center of the vegetal plate region, migrate into the blastocoel (I, J). The vegetal cells will continue to ingress in order to form the archenteron, led by filopodia extending from the secondary mesenchyme cells (SMCs), which eventually contact the animal pole at the future site of mouth formation (K). A prism (not shown) and finally a feeding pluteic larva will be formed 24 h later around an endoskeleton, which contains two spicules made of calcium carbonate secreted by the PMCs (L). A few days later, this pluteus will metamorphose into a tiny male or female adult urchin.
Mentions: Ciliogenesis occurs during sea urchin embryo development immediately prior to hatching into a swimming blastula and it ensures embryo motility up to the feeding pluteic larva stage. After fertilization, a series of rapid cleavages gives rise to a blastoderm consisting of several hundred cells arranged as a spherical monolayer of epithelial cells surrounding the blastocoel (Figure 1, A–G). At this stage, each blastomere synthesizes during interphase one single motile cilium (Figure 1H), itself composed of an axoneme made of a scaffold of nine doublet and two singlet microtubules and several hundred additional proteins attached to a basal body (Dutcher, 1995; Dawe et al., 2007; Silverman and Leroux, 2009). In the sea urchin swimming embryo, as in other multicellular models, the cilia emanate from basal bodies situated right under the apical surface of blastula epithelial cells (Stephens, 2008). During mitosis, each cell retracts and disassembles its axoneme, builds a mitotic spindle with the centrioles as spindle poles, divides, and then returns its centriole pair to the apical cell surface to grow a new cilium (Masuda and Sato, 1984; Dawe et al., 2007). Ciliogenesis is linked to the animal–vegetal cell polarity in the sea urchin embryo. While the blastula starts gastrulating (Figure 1I), the vegetal blastomeres grow short and very active cilia, which follow a metachronic beating movement coordinated along the animal–vegetal axis to provide directional motility to the blastula and propel it in seawater (Stephens, 1995). On the animal side a small group of epithelial cells, which appear thicker than the vegetal cells, form longer and poorly active cilia, which protrude anteriorly to the embryo in an entangled way (Figure 1, I–K). This “apical tuft” plays the role of rudder, preventing random swimming (Stephens, 2008).

Bottom Line: We found that in the early embryo aPKC is uniformly cortical and becomes excluded from the vegetal pole during unequal cleavages at the 8- to 64-cell stages.A dose-dependent and reversible inhibition of aPKC results in mislocalization of the kinase, defective ciliogenesis, and lack of swimming.Thus, as in the primary cilium of differentiated mammalian cells, aPKC controls the growth of motile cilia in invertebrate embryos.

View Article: PubMed Central - PubMed

Affiliation: Observatoire Océanologique, Biologie du Développement, Université Pierre et Marie Curie and CNRS, Villefranche-sur-Mer, France. pruliere@obs-vlfr.fr

ABSTRACT
The atypical protein kinase C (aPKC) is part of the conserved aPKC/PAR6/PAR3 protein complex, which regulates many cell polarity events, including the formation of a primary cilium at the apical surface of epithelial cells. Cilia are highly organized, conserved, microtubule-based structures involved in motility, sensory processes, signaling, and cell polarity. We examined the distribution and function of aPKC in the sea urchin embryo, which forms a swimming blastula covered with motile cilia. We found that in the early embryo aPKC is uniformly cortical and becomes excluded from the vegetal pole during unequal cleavages at the 8- to 64-cell stages. During the blastula and gastrula stages the kinase localizes at the base of cilia, forming a ring at the transition zone between the basal body and the elongating axoneme. A dose-dependent and reversible inhibition of aPKC results in mislocalization of the kinase, defective ciliogenesis, and lack of swimming. Thus, as in the primary cilium of differentiated mammalian cells, aPKC controls the growth of motile cilia in invertebrate embryos. We suggest that aPKC might function to phosphorylate kinesin and so activate the transport of intraflagellar vesicles.

Show MeSH
Related in: MedlinePlus