title: The apical lamina and its role in cell adhesion in sea urchin embryos.
abstract: The hyaline layer (HL) is an extracellular matrix surrounding sea urchin embryos which has been implicated in a cell adhesion and morphogenesis. The apical lamina (AL) is a fibrous meshwork that remains after removal of hyalin from the HL and the fibropellins (FP) are glycoproteins thought to be the principal components of the AL. Using anti-FP antibodies (AL-1 and AL-2) we report immunoprecipitations and affinity purifications yield a high molecular weight complex comprised of the FP glycoproteins. The three components form a complex, stabilized by disulphide cross-linking and have stochiometric ratios of 2 FPIa molecules to 1 each of FPIb and FPIII. Pulse chase experiments indicate all 3 FP's are synthesized throughout development with peaks in synthesis during cleavage and a sustained peak beginning at hatching. Using immunogold and immunoperoxidase localization, the FP localize to a fibrillar complex forming the innermost layer of the HL. In cell adhesion experiments, cells adhere to affinity purified FP in a temperature, time and concentration dependent manner. Cell adhesion to Fp is about 70% of that seen when hyalin is used as a substrate. Pretreating with AL-1 and AL-2 reduces in vitro cell adhesion by about 65%. We conclude FP's form a fibrillar complex, which is synthesized throughout early development and functions, with other components of the HL, as a substrate for cell adhesion.
authors.affiliation: Dept. of Biology, University of Victoria, B.C. Canada. rburke@uvic.ca
authors.forename: R D
authors.initials: RD
authors.lastname: Burke
authors.forename: M
authors.initials: M
authors.lastname: Lail
authors.forename: Y
authors.initials: Y
authors.lastname: Nakajima
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D002448:Cell Adhesion; D002846:Chromatography, Affinity; D004591:Electrophoresis, Polyacrylamide Gel; D004625:Embryo, Nonmammalian / Q000166:cytology / Q000378:metabolism; D004815:Epidermal Growth Factor / Q000096:biosynthesis / Q000737:chemistry / Q000276:immunology / Q000302:isolation & purification / Q000502:physiology*; D005109:Extracellular Matrix / Q000502:physiology*; D016326:Extracellular Matrix Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000276:immunology / Q000302:isolation & purification / Q000502:physiology*; D006818:Hyalin / Q000502:physiology; D007150:Immunohistochemistry; D046911:Macromolecular Substances; D011233:Precipitin Tests; D012617:Sea Urchins / Q000196:embryology*
chemical_list: D000911:Antibodies, Monoclonal; D016326:Extracellular Matrix Proteins; D046911:Macromolecular Substances; C062354:fibropellin protein, sea urchin; D004815:Epidermal Growth Factor