Differential localization of P-selectin and von Willebrand factor during megakaryocyte maturation.
An important step in megakaryocyte maturation is the appropriate assembly of at least two distinct subsets of alpha-granules. The mechanism that sorts the alpha-granule components into distinct structures and mediates their release in response to specific stimuli is now emerging. P-selectin and von Willebrand factor are two proteins present in the alpha-granules that recognize P-selectin glycoprotein ligand on neutrophils and collagen in the subendothelial matrix. These proteins may play an important role in determining the differential release of the alpha-granule contents in response to external stimuli. If P-selectin and von Willebrand factor are localized in the same or different alpha-granules is not known. To clarify this question, we analyzed by immunoelectron microscopy the localization of von Willebrand factor and P-selectin during the maturation of wild-type and Gata1(low) megakaryocytes induced in vivo by treating animals with thrombopoietin. Gata1(low) is a hypomorphic mutation that blocks megakaryocyte maturation, reduces the levels of von Willebrand factor expression and displaces P-selectin on the demarcation membrane system. The maturation block induced by this mutation is partially rescued by treatment in vivo with thrombopoietin. In immature megakaryocytes, both wild-type and Gata1(low), the two receptors were co-localized in the same cytoplasmic structures. By contrast, the two proteins were segregated to separate alpha-granule subsets as the megakaryocytes matured. These observations support the hypothesis that P-selectin and von Willebrand factor may ensure differential release of the alpha-granule content in response to external stimuli.
Zingariello
M
M
Department of Biomorphology, University of Chieti, Chieti, Italy.
Fabucci
M E
ME
Bosco
D
D
Migliaccio
A R
AR
Martelli
F
F
Rana
R A
RA
Zetterberg
E
E
D000818:Animals; D002454:Cell Differentiation; D050982:GATA1 Transcription Factor / Q000235:genetics / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D008533:Megakaryocytes / Q000166:cytology* / Q000378:metabolism*; D051379:Mice; D016253:Microscopy, Immunoelectron; D019007:P-Selectin / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics; D013154:Spleen / Q000737:chemistry / Q000166:cytology; D014841:von Willebrand Factor / Q000378:metabolism*
D050982:GATA1 Transcription Factor; C494689:Gata1 protein, mouse; D019007:P-Selectin; D011994:Recombinant Proteins; D014841:von Willebrand Factor