ABSTRACT. Histo-blood group O has only rarely been observed in baboon. Recent discovery of such an animal has provided us the opportunity to investigate the molecular genetics of the ABO locus in baboons. The major baboon prototype O allele, observed in two homozygous and several heterozygous animals, is related to the A allele as is the case in humans. Additional apparent prototype O alleles have been observed in heterozygotes, one of which is related to the B allele. The nucleotide changes conferring the O phenotype in the two known human O alleles have not been observed in any baboon allele. This information will aid the identification of baboons useful for the development of xenotransplantation in humans.

Keywords: ABO glycotransferase, baboon, glycosyltransferase, histo-blood group, xenotransplantation.

Reprint requests to: David C. Diamond, Ph.D., Center for Molecular Biology and Gene Therapy, Loma Linda University, Loma Linda, CA 92350, phone: (909) 824-4300, ext. 81370, fax: (909) 478-4177, email: ddiamond@ccmail.llu.edu.

ABSTRACT. Guinea pig bone marrow megakaryocytes were isolated and cultured on collagen gels to promote proplatelet formation. In control cultures 15.6% of the cells formed proplatelets. Both IL6 and TPO stimulated dose dependent increases in the percent of proplatelet forming cells up to 26.7% at 100 ng/ml IL6 and 26.8% at 100 ng/ml TPO. IL1 and IL3 had no effect on proplatelet formation. IL3 in combination with IL6 and TPO blocked the increase in proplatelet formation observed with IL6 or TPO alone. IL3 was also found to stimulate thymidine incorporation in megakaryocytes. The role of phosphorylation in proplatelet formation was studied using certain inhibitors. The tyrosine kinase inhibitor genestien had no effect on proplatelet formation at concentrations up to 100 microg/ml. The phosphatase inhibitors calyculin A and okadaic acid both inhibited proplatelet formation. The phosphodiesterase inhibitor isobutylmethylxanthine (IBMX) was a potent stimulator of proplatelet formation. Studies on protein phosphorylation revealed that IL6, but not TPO, stimulated phosphorylation of JAK1, JAK2 and MAP kinase. TPO did stimulate tyrosine phosphorylation of Tyk-2. Although IBMX stimulated proplatelet formation, it inhibited phosphorylation of JAKs and MAP kinase. Adhesion of megakaryocytes to collagen gel also inhibited phosphorylation of JAK1 and JAK2, while MAP kinase phosphorylation was unaffected. These data show that IL6 and TPO stimulate megakaryocyte proplatelet formation. In addition, although these cytokines increase phosphorylation of signal transduction proteins in the JAK/STAT pathway, it appears that a different signal transduction pathway regulated by a combination of phosphatase activity and cAMP levels, leads to proplatelet formation.

Keywords: Megakaryocytopoiesis, signal transduction, growth factors, thrombopoietin, platelet formation.

Reprint requests to: Robert M. Leven, Ph.D., Department of Anatomy, Rush Medical College, 1653 West Congress Parkway, Chicago, IL 60612, phone: (312) 942-6779, fax: (312) 942-5744, e-mail: rleven@rush.edu.

ABSTRACT. Two mutations have been described on the gene considered to be responsible for genetic hemochromatosis, the HLA-H or HFE gene. The C282Y mutation is a disease-causing mutation in most cases of genetic hemochromatosis, but involvement of the H63D substitution in the pathogenesis of the disease is unclear. Compound heterozygotes for both substitutions could help to determine whether or not the second mutation is a worsening factor when associated in trans with the C282Y mutant. We found twenty nine compound heterozygotes during DNA analysis of patients referred to our laboratory for the screening of those mutations. Clinical and biological data were obtainable for 23 of them. Compound heterozygotes could be divided into two groups: subjects with or without iron overload. Five (22%) individuals had normal ferritin levels, whereas 18 had elevated ferritin concentrations (78%). Among those 18 patients, 7 (30% of the total) had clinical and biological criteria of genetic hemochromatosis. Eleven had iron overload without all the criteria of genetic hemochromatosis. Such a high proportion of genetic hemochromatosis is not found in heterozygotes for the C282Y mutation alone neither in our series nor in the literature. Compound heterozygotes for the C282Y and the H63D mutations may have a higher risk of iron overload or genetic hemochromatosis than single heterozygotes for the C282Y mutation. We propose a schematic theoretical representation that could explain this fact at the protein level. Further fundamental studies on the protein, and clinical follow up of compound heterozygotes could help to ascertain this hypothesis.

Keywords: Iron, HFE gene, hemochromatosis, compound heterozygotes.

Reprint requests to: Dr. Patricia Aguilar-Martinez, M.D.,Ph.D., Laboratoire d'Hématologie, Hôpital Saint Eloi, Avenue Bertin Sans, 34295 Montpellier, cedex 5, France, phone: (33) 4 67 33 70 31, fax: (33) 4 67 33 70 36, e-mail: schvedjf@aol.com.