|
We have examined immunocytochemically the expression, localization and in vivo
function of a calcium-dependent and galactose-binding 14 x 10(3) Mr lectin
purified from the budding tunicate, Polyandrocarpa misakiensis. Lectin granules
first appeared in the inner epithelium of a double-walled bud vesicle. Soon
after the bud entered the developmental phase, the granules were secreted into
the mesenchymal space, where the lectin-positive extracellular matrix (ECM)
developed. The lectin was also produced and secreted by granular leucocytes
during budding. Hemoblasts, pluripotent stem cells in the blood, were often
found in association with the ECM and they aggregated with epithelial cells to
form organ rudiments. The lectin showed a high binding affinity for hemoblast
precursors. The blockage of epithelial transformation of stem cells by galactose
in in vivo bioassy was ineffective in the presence of the lectin. Polyclonal
anti-lectin antibody prevented the hemoblasts spreading on the ECM and moving
toward the epithelium, but it did not block the cell-cell adhesion of
hemoblasts. By three days of bud development, lectin granules and ECM have
almost disappeared from the developing bud together with a cessation of
hemoblast aggregation. These results show that Polyandrocarpa lectin is a
component of the ECM induced specifically in budding and suggest strongly that
it plays a role in bud morphogenesis by directing the migration of pluripotent
stem cells to the epithelium.
|
