α-parvin is required for epidermal morphogenesis, hair follicle development and basal keratinocyte polarity

Epidermal morphogenesis and hair follicle (HF) development depend on the ability of keratinocytes to adhere to the basement membrane (BM) and migrate along the extracellular matrix. Integrins are cell-matrix receptors that control keratinocyte adhesion and migration, and are recognized as major regulators of epidermal homeostasis. How integrins regulate the behavior of keratinocytes during epidermal morphogenesis remains insufficiently understood. Here, we show that α-parvin (α-pv), a focal adhesion protein that couples integrins to actin cytoskeleton, is indispensable for epidermal morphogenesis and HF development. Inactivation of the murine α-pv gene in basal keratinocytes results in keratinocyte-BM detachment, epidermal thickening, ectopic keratinocyte proliferation and altered actin cytoskeleton polarization. In vitro, α-pv-null keratinocytes display reduced adhesion to BM matrix components, aberrant spreading and stress fibers formation, and impaired directed migration. Together, our data demonstrate that α-pv controls epidermal homeostasis by facilitating integrin-mediated adhesion and actin cytoskeleton organization in keratinocytes

Horizontal gene transfer contributed to the evolution of extracellular surface structures

The single-cell layered ectoderm of the fresh water polyp Hydra fulfills the function of an epidermis by protecting the animals from the surrounding medium. Its outer surface is covered by a fibrous structure termed the cuticle layer, with similarity to the extracellular surface coats of mammalian epithelia. In this paper we have identified molecular components of the cuticle. We show that its outermost layer contains glycoproteins and glycosaminoglycans and we have identified chondroitin and chondroitin-6-sulfate chains. In a search for proteins that could be involved in organising this structure we found PPOD proteins and several members of a protein family containing only SWT (sweet tooth) domains. Structural analyses indicate that PPODs consist of two tandem β-trefoil domains with similarity to carbohydrate-binding sites found in lectins. Experimental evidence confirmed that PPODs can bind sulfated glycans and are secreted into the cuticle layer from granules localized under the apical surface of the ectodermal epithelial cells. PPODs are taxon-specific proteins which appear to have entered the Hydra genome by horizontal gene transfer from bacteria. Their acquisition at the time Hydra evolved from a marine ancestor may have been critical for the transition to the freshwater environment

α-parvin controls vascular mural cell recruitment to vessel wall by regulating RhoA/ROCK signalling

During blood vessel development, vascular smooth muscle cells (vSMCs) and pericytes (PCs) are recruited to nascent vessels to stabilize them and to guide further vessel remodelling. Here, we show that loss of the focal adhesion (FA) protein α-parvin (α-pv) in mice leads to embryonic lethality due to severe cardiovascular defects. The vascular abnormalities are characterized by poor vessel remodelling, impaired coverage of endothelial tubes with vSMC/PCs and defective association of the recruited vSMC/PCs with endothelial cells (ECs). α-pv-deficient vSMCs are round and hypercontractile leading either to their accumulation in the tissue or to local vessel constrictions. Because of the high contractility, α-pv-deficient vSMCs fail to polarize their cytoskeleton resulting in loss of persistent and directed migration. Mechanistically, the absence of α-pv leads to increased RhoA and Rho-kinase (ROCK)-mediated signalling, activation of myosin II and actomyosin hypercontraction in vSMCs. Our findings show that α-pv represents an essential adhesion checkpoint that controls RhoA/ROCK-mediated contractility in vSMCs

Horizontal gene transfer contributed to the evolution of extracellular surface structures: the freshwater polyp Hydra is covered by a complex fibrous cuticle containing glycosaminoglycans and proteins of the PPOD and SWT (sweet tooth) families.

The single-cell layered ectoderm of the fresh water polyp Hydra fulfills the function of an epidermis by protecting the animals from the surrounding medium. Its outer surface is covered by a fibrous structure termed the cuticle layer, with similarity to the extracellular surface coats of mammalian epithelia. In this paper we have identified molecular components of the cuticle. We show that its outermost layer contains glycoproteins and glycosaminoglycans and we have identified chondroitin and chondroitin-6-sulfate chains. In a search for proteins that could be involved in organising this structure we found PPOD proteins and several members of a protein family containing only SWT (sweet tooth) domains. Structural analyses indicate that PPODs consist of two tandem β-trefoil domains with similarity to carbohydrate-binding sites found in lectins. Experimental evidence confirmed that PPODs can bind sulfated glycans and are secreted into the cuticle layer from granules localized under the apical surface of the ectodermal epithelial cells. PPODs are taxon-specific proteins which appear to have entered the Hydra genome by horizontal gene transfer from bacteria. Their acquisition at the time Hydra evolved from a marine ancestor may have been critical for the transition to the freshwater environment

SWT (sweet tooth) proteins identified in the salt wash by MS/MS.

<p>SWT (sweet tooth) proteins identified in the salt wash by MS/MS.</p

PPOD agglutinates erythrocytes.

<p>Haemagglutination assays with rabbit erythrocytes. A: Addition of increasing amounts PPOD4 protein agglutinates erythrocytes and prevents their sedimentation (dark dot at 0 µl PPOD4 indicates sedimentation of erythrocytes, which are not agglutinated). Addition of mannose or glucose does not prevent PPOD4 induced agglutination. B: Erythrocytes sediment in the absence of PPOD4 protein (lower row). Addition of PPOD4 prevents this due to agglutination. Addition of heparin or chondroitin (GalNAc-4-SO4) to PPOD prevents PPOD4 induced agglutination in a concentration dependent manner.</p

Soluble protein content of hypertonic salt wash.

<p>A: SDS-PAGE gel of 0.2 M NaCl wash stained with coomassie. Major bands were excised and identified by mass spectrometry. Positions of the PPOD 2, 3 and 4 bands are indicated. Bands 1–4 represent members of SWT protein family. See text for details. B: Immunoblot for this gel stained with anti-PPOD4 antibody.</p

Immuno-EM localisation of PPOD.

<p>A: Immunogold labeling of PPOD (visualised by anti-chicken 10 nm colloidal gold) in the cuticle layer c5 and in subapical secretory granules (s) of ectodermal epithelial cells. Freeze-substitution with pure acetone followed by LR-white embedding. Scale bar: 200 nm. B: PPOD-positive secretory granule (s) in contact (arrow-head) with the plasma membrane (pm). Scale bar: 200 nm. C: Subapical secretory granules (s) are all PPOD-positive. A mitochondrium is lettered with (m), the plasma membrane with (pm). Scale bar: 200 nm. D: Scarce PPOD-immunogold-labelling can also be seen throughout cuticle layers c2–4 (marked by arrows), in addition to PPOD-labelling of layer c5 (double arrows). Scale bar: 500 nm.</p