Summary
Lesions in the genes for GPIbα, GPIbβ or GPIX result in a bleeding diathesis, the
Bernard-Soulier syndrome (BSS), which associates a platelet adhesion defect with thrombocytopenia,
giant platelets and abnormal megakaryocytes (MK). The role of GPV, also absent in
BSS, was recently addressed by gene targeting in mice. While a negative modulator
function for GPV on thrombin-induced platelet responses was found in one model, the
absence of GP V had no effect on GPIb-IX expression or platelet adhesion. Our study
extends previous results and reports that electron microscopy of bone marrow from
the GPV knockout mice revealed a normal MK ultrastructure and development of the demarcation
membrane system (DMS). There was a usual presence of MK fragments in the bone marrow
vascular sinus. Immunogold labelling of MK from the knockout mice showed a normal
distribution of GPIb-IX in the DMS and on the cell surface. The distribution of fibrinogen,
vWF and P-selectin was unchanged with, interestingly, P-selectin also localised within
the DMS in both situations. Thus GPV is not crucial to MK development and platelet
production, consistent with the fact that no mutation in the GPV gene has as yet been
described in BSS.
Key words
GPV knockout mice - GPIb-IX - megakaryocytes - electron microscopy
