Fetal hemoglobin restriction to a few erythrocytes (F cells) in normal human adults.

During adult life, the quantity of fetal hemoglobin (HbF) present in F cells--that is, rare erythrocytes which are reactive with rabbit antiserum to human HbF during microscopic immunodiffusion--is sufficient to account for all of the small quantity (less than 0.7 percent) of HbF normally present in whole blood. Thus, erythrocytes are normally heterogeneous with respect to the presence of HbF.

Increased nerve-growth-factor beta-chain cross-reacting material in familial dysautonomia.

To determine whether dysautonomia arises from alteration in nerve-growth factor (NGF), we measured serum levels of NGF subunits in normal and dysautonomic subjects using a biologic assay based on neurite outgrowth from chick ganglions, a binding assay based on displacement of radiolabeled betaNGF from rabbit-ganglion microsomes, and radioimmunoassays of chi, gamma and betaNGF subunits via antiserum to mouse NGF polypeptides. A threefold increase (P less than 0.001) in serum antigen levels of the biologically active subunit (betaNGF) was found for dysautonomic as compared with normal subjects. By all other assays, the groups were alike. The marked discrepancy in betaNGF levels between antigenic and functional (biologic and binding) measurements suggests a qualitative abnormaltiy of betaNGF in dysautonomia. Alternatively, elevation of betaNGF antigen can be regarded as secondary to disease. This alternative seems less likely since we must then suppose that the normalcy of functional assays in spurious.

Inheritance of F cell frequency in heterocellular hereditary persistence of fetal hemoglobin: an example of allelic exclusion.

Two kindreds are described in which F cell frequency is inherited. These families differ in ethnic origin, the mean quantity of HbF per F cell, and in G gamma: A gamma ratios. Heterozygotes have approximately 50% F cells while homozygotes have close to 100%. Semiquantitative single cell immunodiffusion assays establish that F cells contain all of the HbF found in heterozygotes. Our finding that the gene for this heterocellular form of hereditary persistence of fetal hemoglobin is expressed in only half the cells provides the first example of allelic exclusion known apart from immunoglobulin expression.

Production of F cells in sickle cell anemia: regulation by a genetic locus or loci separate from the beta-globin gene cluster.

Levels of fetal hemoglobin (HbF) bearing reticulocytes (F reticulocytes) range from 2% to 50% in patients with sickle cell (SS) anemia. To learn whether any portion of such variation in F cell production is regulated by loci genetically separable from the beta-globin gene cluster, percentages of F reticulocytes were compared in 59 sib pairs composed solely of SS members, including 40 pairs from Jamaica and 19 from the United States. We reasoned that differences in F reticulocyte levels might arise (1) from any of several kinds of artifact, (2) via half-sib status, or (3) because one or more genes regulating F cell production segregate separately from beta S. We minimized the role of artifact by assay of fresh samples from 84 SS individuals, including both members of 38 sib pairs. In 78 of the 84 subjects, serial values for percent F reticulocytes fell within 99.9% confidence limits or were alike by t test (P greater than or equal to .05). This left 32 sib pairs for which F reticulocyte levels in each member were reproducible. When sib-sib comparisons were limited to these 32 pairs, percentages of F reticulocytes were grossly dissimilar within 12 Jamaican and 3 American sibships. Within them, the probability that sibs were alike was always less than or equal to .005 and usually less than or equal to 10(-4). We next minimized the contribution of half-sibs among Jamaicans by a combination of paternity testing and sib-sib comparison of beta-globin region DNA restriction fragment length polymorphisms, especially among discordant pairs. We thereafter concluded that at least seven to eight Jamaican pairs were composed of reproducibly discordant full sibs. There is thus little doubt that there are genes regulating between-patient differences in F cell production that are separate from the beta-globin gene cluster. Still unanswered is (1) whether or not these genes are actually linked to beta S, (2) why F reticulocyte levels in Americans tend to be lower than in Jamaicans, and (3) whether or not differences in F cell production among SS patients are regulated by several major loci or by only one.

Origin of the human L1 elements: proposed progenitor genes deduced from a consensus DNA sequence.

A consensus sequence for the human long interspersed repeated DNA element, L1Hs (LINE or KpnI sequence), is presented. The sequence contains two open reading frames (ORFs) which are homologous to ORFs in corresponding regions of L1 elements in other species. The L1Hs ORFs are separated by a small evolutionarily nonconserved region. The 5' end of the consensus contains frequent terminators in all three reading frames and has a relatively high GC content with numerous stretches of weak homology with AluI repeats. The 5' ORF extends for a minimum of 723 bp (241 codons). The 3' ORF is 3843 bp (1281 codons) and predicts a protein of 149 kD which has regions of weak homology to the polymerase domain of various reverse transcriptases. The 3' end of the consensus has a 208-bp nonconserved region followed by an adenine-rich end. The organization of the L1Hs consensus sequence resembles the structure of eukaryotic mRNAs except for the noncoding region between ORFs. However, due to base substitutions or truncation most elements appear incapable of producing mRNA that can be translated. Our observation that individual elements cluster into subfamilies on the basis of the presence or absence of blocks of sequence, or by the linkage of alternative bases at multiple positions, suggests that most L1 sequences were derived from a small number of structural genes. An estimate of the mammalian L1 substitution rate was derived and used to predict the age of individual human elements. From this it follows that the majority of human L1 sequences have been generated within the last 30 million years. The human elements studied here differ from each other, yet overall the L1Hs sequences demonstrate a pattern of species-specificity when compared to the L1 families of other mammals. Possible mechanisms that may account for the origin and evolution of the L1 family are discussed. These include pseudogene formation (retroposition), transposition, gene conversion, and RNA recombination.