Human platelet glycoprotein Ib (GP Ib) i s a major integral membrane protein that has been identified as the platelet-binding site mediating the factor VIII/von Willebrand-factor-dependent adhesion of platelets to vascular subendothelium. Recent evidence suggests that G P Ib is normally coinplexed with another platelet membrane protein, GP IX. In this study, human platelet plasma membranes were selectively solubilized with a buffer containing 0.1% (v/v) Triton X-100. The GPIb complex (GPIb plus GPIX) was purified to homogeneity in = 30% yield by immunoaffinity chromatography of the membrane extract using the anti-(glycoprotein Ib complex) murine monoclonal antibody, WM 23, coupled to agarose. G P Ib and GP IX were subsequently isolated as purified components by immunoaffinity chromatography of the GP Ib complex using a second anti-(glycoprotein Ib complex) monoclonal antibody, FMC 25, coupled to agarose. As assessed by dodecyl sulphate/ polyacrylamide gel electrophoresis, purified GP Ib was identical to the molecule on intact platelets and had an apparent relative molecular mass of 170000 under nonreducing conditions and 135000 (cr subunit) and 25000 (p subunit) under reducing conditions. GP IX had an apparent M , of 22000 under both nonreducing and reducing conditions. Purified Gb Ib complex and GP Ib inhibited the ristocetin-mediated, human factor VIII/von Willebrand-factor-dependent and bovine factor VIII/von Willebrand-Factor-dependent agglutination of washed human platelets suggesting the proteins had been isolated in functionally active form. G P Ib, had a similar amino acid composition to that previously reported for its proteolytic degradation product, glycocalicin. The amino acid compositions of GP Ib, and GP IX were similar but showed marked differences in the levels of glutamic acid, alanine, histidine and arginine. The N-termini of GP Ib, and G P 1X were blocked; G P Ib, had the N-terminal sequence, Ile-Pro-Ala-Pro-. On crossed immunoelectrophoresis, both GP Ib and GP IX were found to occur in the same immunoprecipitin arc(s) whether the platelets had been solubilized in the absence or presence of the calcium-dependent protease inhibitor, leupeptin. Binding studies in platelet-rich plasma indicated a similar number of binding sites (2 I: SD) for three anti-(glycoprotein Ib complex) monoclonal antibodies: AN 51, epitope on GP Ib, (22000 I: 2700, n = 3), WM 23, epitope on G P Ib, (21 000 3400, n = 3), FMC 25, epitope on GP IX (20100 f 2700, n = 3), and FMC 25 (Fab')2 (27100 800, n = 2). The combined evidence suggests that GP Ib is normally bound to GP IX and that the stoichioinetry of this complex is 1 : 1.The initial event in hemostasis in response to vascular injury involves the adhesion of platelets to the exposed vascular subendothelium. The adhesion reaction appears to be dependent on three components [I]: a receptor on platelets which on the basis of a variety of evidence has been defined as the platelet membrane protein, glycoprotein Ib (GP Ib); a plasma component, factor VIII/von Willebrand fac...

Inherited retinal dystrophies are the most common cause of childhood blindness in the developed world. Cone-rod retinal dystrophies are severe examples of this group of disorders. Analysis of a large cone-rod dystrophy pedigree suggested that inheritance within the family was influenced by meiotic drive (p = 0.008), a rare segregation distortion in human genetics. Two-point linkage analysis showed significant linkage with three markers mapping to chromosome 19q. Multipoint analysis gave a maximum lod score of 10.08 (theta = 0.05) distal to D19S47. Cone-rod dystrophy is therefore assigned to 19q13.1-q13.2 and a new candidate locus for other retinal dystrophies is identified.

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Rod/cone dysplasia type one (rcd-1) is an early onset inherited retinal dystrophy segregating in the Irish setter breed. It is classed as one of the autosomal recessive canine generalised Progressive Retinal Atrophies (PRA). The disease results in complete loss of photoreceptors by approximately one year of age. Levels of retinal cGMP are markedly elevated and of abnormal distribution in rod photoreceptors. Rod phosphodiesterase activity is absent and mRNA encoding the beta subunit (PDE beta) of the holoenzyme is uniquely reduced in predegenerate retinae. Using retinae from normal, unrelated adult dogs we have PCR-amplified and sequenced the cDNA for PDE beta. The cDNA is almost identical to that recently described for the Irish setter in the USA apart from two translationally silent single nucleotide changes. Using carrier and affected setters from a UK breeding colony we have screened genomic DNA and can confirm the G to A transition in rcd-1 affected dogs at position 2420, creating an amber mutation in codon 807. However, PRA-affected Tibetan terriers and miniature longhaired dachshunds are normal at this locus, underlining the genetic heterogeneity of this disease group. In addition we have developed a rapid, PCR-based diagnostic test for this mutation that will differentiate normal dogs from asymptomatic carriers.