Basement membrane lectin binding sites are decreased in the esophageal endoderm during the arrival of presumptive muscle mesenchyme in the developing asteroid Pisaster ochraceus.
Basement membranes (BMs) of vertebrates and invertebrates have been shown to contain glycoproteins and proteoglycans, which include oligosaccharides and glycosaminoglycans. Lectin binding sites were characterized in the BM of gastrulating embryos of the starfish, Pisaster ochraceus. In early and mid-gastrulae, the fluorescein isothiocyanate (FITC)-lectin conjugates of concanavalin A (Con A) and wheat germ agglutinin (WGA) reveal the presence of mannose/glucose and glucosamine/sialic acid residues in the BM of all regions of the embryos. However, in the late gastrula embryo, an apparent reduction of these components is observed over the esophageal BM. Ultrastructural studies using the lectin-gold conjugates Con A, Limax flavus agglutinin (LFA), specific for sialic acid, and Dolichos biflorus agglutinin (DBA), specific for galactosamine, demonstrate that most mannose/glucose and galactosamine-containing residues lie in the lamina densa, whereas most sialic acid residues are located over the lamina lucida. In addition, a statistical analysis of lectin binding in the late gastrula embryo reveals that the amount of labelling with both Con A and LFA is significantly reduced in the esophageal region, suggesting that mannose/glucose and sialic acid residues are reduced in this region. These results confirm the observations of the FITC-lectin studies described above. They also confirm earlier studies that demonstrated a difference in BM morphology of the esophageal region (Crawford, '88). Mesenchyme cells, some of which arise from the forming coeloms (Crawford, '90), and which may represent a distinct population, colonize exclusively on this esophageal BM, where they later differentiate into muscle. Quantitative differences in BM glycoconjugates may act to direct the presumptive muscle cells to the region of the esophagus.
Reimer
C L
CL
Department of Anatomy, University of British Columbia, Vancouver.
Crawford
B J
BJ
Crawford
T J
TJ
D000818:Animals; D001485:Basement Membrane / Q000737:chemistry / Q000648:ultrastructure; D004707:Endoderm / Q000737:chemistry / Q000648:ultrastructure; D004947:Esophagus / Q000737:chemistry / Q000648:ultrastructure; D006046:Gold; D006651:Histocytochemistry; D009132:Muscles / Q000196:embryology / Q000648:ultrastructure; D011975:Receptors, Mitogen / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D013215:Starfish / Q000196:embryology* / Q000648:ultrastructure
D011975:Receptors, Mitogen; D006046:Gold