Convergent extension movements in growth plate chondrocytes require gpi-anchored cell surface proteins

Abstract

Proteins that are localized to the cell surface via glycosylphosphatidylinositol (gpi) anchors have been proposed to regulate cell signaling and cell adhesion events involved in tissue patterning. Conditional deletion of Piga, which encodes the catalytic subunit of an essential enzyme in the gpi-biosynthetic pathway, in the lateral plate mesoderm results in normally patterned limbs that display chondrodysplasia. Analysis of mutant and mosaic Piga cartilage revealed two independent cell autonomous defects. First, loss of Piga function interferes with signal reception by chondrocytes as evidenced by delayed maturation. Second, the proliferative chondrocytes, although present, fail to flatten and arrange into columns. We present evidence that the abnormal organization of mutant proliferative chondrocytes results from errors in cell intercalation. Collectively, our data suggest that the distinct morphological features of the proliferative chondrocytes result from a convergent extension-like process that is regulated independently of chondrocyte maturation.

Cell polarity

“…For example, in the growth plate, loss of oriented cell behaviors leads to loss of proliferative column structure and generates bones that are reduced in length and greater in width. 46,81 One simple model derived from these observations is that oriented cell behaviors provide a driving force for tissue elongation in the developing skeleton, 46,84 analogous to a model previously proposed for events in zebrafish gastrulation. 85 In the context of the limb, this model has only been empirically tested in the growth plate, a tissue in which precise measurements of elongation have been performed.…”

“…80 Interestingly, glypicans are anchored to the cell surface by a glycosyl-phosphatidylinositol (GPI) moiety, and mutations in Piga, an essential enzyme for GPI biosynthesis, produce a Knypek-like phenotype in the growth plates of mice. 81 Although a specific role for glypicans in regulating cell polarity via Wnt signaling has not been determined, genetic interactions suggest that Kny might bind Wnt5 and Wnt11, while other studies in zebrafish provide evidence that Kny stabilizes Frizzled receptors on the cell surface. 82 Second, experiments in the chick using a dominant-negative Wnt receptor (dnFzd7) and a dominant-negative Dishevelled (dnDvl) showed a cell autonomous requirement for Wnt signaling to orient division planes and to generate columns in proliferative chondrocytes.…”

“…46 Neither gain nor loss of β-catenin function in chick or in mouse, respectively, prevent column formation, suggesting that non-canonical Wnt signaling, rather than canonical Wnt signaling, regulates oriented cell behaviors in proliferative chondrocytes. 46,81 Failure to align division planes and organize into columns in dnFzd7-and dnDvl-expressing chondrocytes is likely the result of interfering with PCP signaling because introduction of a point mutation analogous to the Drosophila mutant dsh1 (which specifically interferes with PCP signaling) into the C-terminal DEP domain rendered dnDvl inactive. 46,83 Third, recent work demonstrated dose-dependent genetic interactions between the secreted ligand Wnt5a, the receptor tyrosine kinase Ror2 and PCP pathway gene in developing digits.…”

“…This specific example of crosstalk could occur in the limb mesenchyme but is not likely to function in the growth plate, since defects in canonical Wnt signaling do not block chondrocyte column formation in the growth plate. 46,81 However, it remains to be determined whether important roles exist for Ryk or for the PCP-associated tyrosine kinase Ptk7 in modulating the non-canonical Wnt signal during limb development. 96,97 Is cell polarity in the limb regulated by Wnt5a gradients?…”

Spatiotemporal changes in cell adhesiveness during vertebrate limb morphogenesis

“…The limbs in mice lacking PIGA, which encodes PIGA, an enzyme that is involved in the biosynthesis of the GPI-anchor, show severe chondrodysplasia phenotype, and delayed osteogenesis (Ahrens et al, 2009). Despite these skeletal defects, the skeletal pattern in the limb is barely affected, and a rough outline of skeletal pattern appears to be established without a GPI-anchored protein.…”