Mapping studies on a pericentric inversion (18) (p11.31 q21.1) in a family with both schizophrenia and learning disability.

Chromosomal abnormalities that co-occur with psychiatric disorders can be useful direct pointers to the locus of susceptibility genes. Two families with pericentric inversions of chromosome 18, inv 18(p11.3 q21.1) and psychiatric illness have previously been described. We have fine mapped the chromosomal breakpoints of the rearrangement in a clinically well, inversion carrier from one of these families where other inversion carriers suffered from chronic schizophrenia or severe learning disability. Yeast artificial chromosomes (YACs) from the Whitehead/MIT physical maps of human chromosome 18 have been positioned relative to the chromosomal breakpoints and a number of YACs that span these breakpoints have been identified. Linkage and association studies have previously suggested these regions of chromosome 18q and 18p as candidate loci harbouring genes involved in bipolar disorder and schizophrenia.

Chromosomal localization of the human diadenosine 5',5"'-P1,P4-tetraphosphate pyrophosphohydrolase (Ap4A hydrolase) gene (APAH1) to 9p13.

Diadenosine 5',5"'-P1,P4-tetraphosphate (Ap4A) hydrolase is the enzyme responsible for maintaining the intracellular level of the dinucleotide Ap4A, the function of which has yet to be established. The APAH1 gene encoding this Ap4A hydrolase has been mapped by fluorescence in situ hybridization and PCR to human chromosome 9p13. Radiation hybrid panel mapping further located APAH1 between the IL11RA and the GALT genes, thus excluding it as a candidate gene for cartilage-hair hypoplasia, which maps proximal to GALT. Several tumor suppressor genes have previously been mapped within the 9p13-p21 region. Given that the FHIT gene at 3p14.2, which encodes a diadenosine 5',5"'-P1,P3-triphosphate (AP3A) hydrolase, is a candidate tumor suppressor, APAH1 should also be considered a potential tumor suppressor.

Correlation of the exon/intron organization to the secondary structures of the protease domain of mouse meprin alpha subunit.

Metalloendopeptidases of the astacin family contain a homologous protease domain of about 200 amino acids. We now report the genomic structure corresponding to the protease domain for one member of this family, the mouse meprin alpha subunit. This is the first such description for the mammalian meprin subunits. It consists of four small exons (76 to 222 base pairs) and three large introns (2.9 to 4.2 kilobases). The exon/intron organization correlates well with the secondary structure elements of the domain as predicted by computer modeling. Exon Ep1 contains beta strand I, and Ep2 consists of helix A and beta strands II-III. Ep3 corresponds to beta strands IV-V and helix B. Ep4 correlates with helices C and D. Introns Ip1 and Ip2 are present at the beginning of helix A and beta strand IV, respectively, and Ip3 is between helices B and C. Similar analyses of sequences previously published by others, have extended this correlation to other astacin family members from different organisms. The relationship between gene and protein structures within the astacin family provide novel information on the evolution of this family in relation to other gene families.

A candidate gene for mild mental handicap at the FRAXE fragile site.

The cytogenetic expression of the folate sensitive fragile site, FRAXE, is due to the expansion of a GCC repeat in proximal Xq28 of the human X chromosome and is associated with a mild form of mental handicap. Normal individuals have 6-35 copies of the repeat whereas cytogenetically positive, developmentally delayed males have > 200 copies and show methylation of the associated CpG island. Through the use of conserved sequences adjacent to the FRAXE GCC repeat, we have isolated a 1495 bp cDNA which begins 331 bp distal to the FRAXE site and extends to a region > 170 kb distal in Xq28. The cDNA sequence possesses both a putative start of translation and a poly-A tail. The predicted protein has amino acid motifs which share significant homologies with the human AF-4 gene which encodes a putative transcription factor. On northern analysis, the cDNA detects a 9.5 kb transcript in human brain, placenta and lung. This transcript is present in multiple human brain tissues, but is more abundant in the hippocampus and the amygdala, thus providing possible functional insights. RT-PCR of normal adult brain RNA provides evidence for the existence of the 1495 bp transcript represented by the isolated cDNA.

Triplet repeat expansion at the FRAXE locus and X-linked mild mental handicap.

We have recently shown that the expression of the FRAXE fragile site in Xq28 is associated with the expansion of a GCC trinucleotide repeat. In the families studied, FRAXE expression is also associated with mild mental handicap. Here we present data on families that previously had been diagnosed as having the fragile X syndrome but that later were found to be negative for trinucleotide repeat expansion at the FRAXA locus. In these families we demonstrate the presence of a GCC trinucleotide repeat expansion at the FRAXE locus. Studies of the FRAXE locus of normal individuals show that they have 6-25 copies of the repeat, whereas affected individuals have > 200 copies. As in the fragile X syndrome, the amplified CpG residues are methylated in affected males.

Trinucleotide repeat amplification and hypermethylation of a CpG island in FRAXE mental retardation.

We have cloned the fragile site FRAXE and demonstrate that individuals with this fragile site possess amplifications of a GCC repeat adjacent to a CpG island in Xq28 of the human X chromosome. Normal individuals have 6-25 copies of the GCC repeat, whereas mentally retarded, FRAXE-positive individuals have > 200 copies and also have methylation at the CpG island. This situation is similar to that seen at the FRAXA locus and is another example in which a trinucleotide repeat expansion is associated with a human genetic disorder. In contrast with the fragile X syndrome, the GCC repeat can expand or contract and is equally unstable when passed through the male or female line. These results also have implications for the understanding of chromosome fragility.

Identification of the FRAXE fragile site in two families ascertained for X linked mental retardation.

Chromosome fragility in two families not exhibiting amplification of the CGG trinucleotide associated with the fragile X site has been examined. Fluorescence in situ hybridisation with cosmid DNA from loci immediately flanking FRAXA and other distal loci have confirmed that cytogenetic fragility in these subjects is the result of expression of a new folate sensitive fragile X site, FRAXE.

Immunological detection of degradation intermediates of skeletal-muscle glycogen phosphorylase in vitro and in vivo.

Over 95% of the pyridoxal phosphate (PLP) in skeletal is bound to one protein, glycogen phosphorylase. This, and the fact that phosphorylase constitutes approx. 5% of the soluble protein in skeletal muscle, introduce the possibility that PLP might be used as a specific label to identify degradation intermediates of the enzyme. In this investigation, we have developed immunological methods, using a monoclonal antibody to PLP and polyclonal antibodies to phosphorylase, to detect degradation intermediates in vitro and in vivo. We have identified a family of degradation intermediates of glycogen phosphorylase in the high-speed-supernatant fraction of mouse skeletal muscle. These peptides react with both types of antibodies and are in the size and concentration range expected for degradation intermediates in a model in which the committed step is followed by rapid clearance of the products. Changes in amounts of degradation intermediates are examined in physiological or pathological conditions in which the rate of degradation of phosphorylase is altered.

Turnover of glycogen phosphorylase in the pectoralis muscle of broiler and layer chickens.

Glycogen phosphorylase is a major sarcoplasmic protein in chicken pectoralis muscle, constituting approx. 4% of the total protein complement. In slow-growing layer chicks phosphorylase accumulated in parallel with muscle accretion, but in fast-growing broiler chicks the concentration of phosphorylase in the muscle increased (from 5 to 8 mg/g wet wt.) with time. In a 5-week period, the total amount of phosphorylase in the pectoralis muscles increased 18-fold in broiler chicks (from approx. 75 to 1400 mg total), but only 3-fold (from approx. 100 to 270 mg total) in layers. Pyridoxal phosphate, the cofactor of the enzyme glycogen phosphorylase, was used as a specific label to measure the rate of degradation of the enzyme in the pectoralis muscle of growing broiler and layer chickens in vivo. In young animals, the fractional rate of phosphorylase synthesis was similar in broiler and layer chickens (approx. 15%/day), but the rate of degradation in layers (5%/day) was 5-fold higher than in broilers (1%/day). As the animals aged, the rate of synthesis decreased, but more so in layers than in broilers. The rate of degradation of phosphorylase also decreased in layers, but in broilers it remained at the low level seen in young animals. The dramatically higher rate of phosphorylase accretion in the pectoralis muscles of the broilers is therefore achieved by an initial lower rate of degradation combined with a sustained difference between rates of synthesis and degradation.

The alpha subunit of meprin A. Molecular cloning and sequencing, differential expression in inbred mouse strains, and evidence for divergent evolution of the alpha and beta subunits.

Meprin A, a membrane-bound oligomeric metalloendopeptidase, contains two different subunits, alpha and beta. We report here the cloning and sequencing of the alpha subunit cDNA. The translated polypeptide consists of 760 amino acids, including a preprosequence (77 amino acids) that precedes the NH2 terminus of the purified enzyme. The next 198 amino acids constitute the "astacin family" protease domain, which includes the astacin family signature sequence, HE(L,I)XHXXGFXHE(Q,H)XRXDRDX(Y,H)(V,I)X(I,V). An immunoglobulin/major histocompatibility complex protein signature was found at the end of the protease domain. At the COOH terminus of the alpha subunit, there is an epidermal growth factor-like domain, followed by a transmembrane domain, and six additional amino acids. Ten potential glycosylation sites have been identified, and at least three of those sites are glycosylated. Northern blot analyses of kidney tissue from C57BL/6 and C3H/He mice indicate that variations in meprin A activity in these strains reflect differences in the levels of the alpha subunit mRNA. Several internal peptide sequences obtained from the beta subunit indicate that it is approximately 50% identical to the alpha subunit. Furthermore, NH2-terminal sequence analyses (39 residues) indicate that rat and mouse alpha are 79% identical, rat and mouse beta are 74% identical, and that alpha and beta subunits for both species are 47% identical. These data indicate that alpha and beta are closely related products of divergent evolution.

The astacin family of metalloendopeptidases.

Molecular cloning of a human intestinal brush border metalloendopeptidase (N-benzoyl-L-tyrosyl-p-aminobenzoic acid hydrolase, PPH) and a mouse kidney brush border metalloendopeptidase (meprin A) has revealed 82% identity in the NH2-terminal amino acid sequences (198 residues) of the mature enzymes. Furthermore, searching of protein sequence data bases with the inferred peptide sequences as probes revealed strong similarities to astacin, a crayfish digestive protease, and an NH2-terminal domain of a human bone morphogenetic protein (BMP-1). Meprin A and PPH both have approximately 30% identity with astacin and BMP-1. Multiple alignment analysis indicated that 37 residues, including 3 cysteine residues, are strictly conserved for the four proteins in a sequence frame equivalent to the complete 200-amino acid astacin sequence. The four proteins contain a zinc-binding motif (HEXXH), found at the active site of most metalloendopeptidases, within an extended sequence of HEXXHXXGFXHE which is unique to this subgroup of metalloendopeptidases. In addition, the four proteins have 54% identity in a 24-amino acid sequence that includes the putative active site. A fifth protein, Xenopus laevis developmentally regulated protein UVS.2, also shares sequence identity with the metalloendopeptidases. These data provide strong evidence for an evolutionary relationship of these proteins. It is suggested that this new family of metalloendopeptidases be called the "astacin family."

Homo- and heterotetrameric forms of the membrane-bound metalloendopeptidases meprin A and B.

Meprin A and B are disulfide-linked, tetrameric metalloendopeptidases in renal brush border membranes. Meprin A contains 90-kDa subunits (alpha subunits) and is expressed in random-bred and some inbred strains of mice. Meprin B contains subunits of 110 kDa (beta subunits) in situ, and the enzyme from C3H mice, a strain that does not express alpha subunits, has been characterized. Evidence from this and previous studies indicate that beta subunits are expressed in all mouse strains. The tetrameric organization of these meprins was examined in brush border membrane fractions from a random-bred strain (ICR) and two inbred strains of mice (C57BL/6 and C3H/He). Lectin blotting using biotinylated concanavalin A revealed that membranes from the random-bred strain contained three oligomeric complexes of approximately 390, 440, and 490 kDa as determined after sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) in the absence of reducing agents. The subunits in all three oligomers were linked by disulfide bridges. Western blotting using an anti-alpha monoclonal antibody indicated that alpha subunits (90 kDa) were present in the 390- and 440-kDa complexes. Western blotting with a polyclonal antibody specific for beta subunits (110 kDa) indicated the presence of these subunits in the 440- and 490-kDa complexes. Electroelution of the individual oligomers followed by SDS-PAGE under reducing conditions confirmed that the 390- and 490-kDa molecules are homotetramers of alpha and beta subunits, respectively, and that the 440-kDa molecule is a heterotetramer consisting of disulfide-bridged alpha and beta subunits. C57BL/6 mice expressed both alpha and beta subunits and contained tetramers composed of alpha 4 and alpha 2 beta 2. C3H/He mice expressed only the 110-kDa beta subunits and the beta 4 oligomer. This type of multimeric organization of disulfide-linked subunits is unique for the known endopeptidases.

Immunological characterisation of different meprin species in mice.

Meprin-a is a metalloendopeptidase present at high levels in the kidney brush border of some inbred mouse strains. Meprin-b is a latent metallo-endopeptidase, activated by trypsin-mediated proteolysis in vitro, that is present at similar activities (after activation) in all mouse strains. Meprin (a mixture of a and b forms) was purified from a high-meprin Mep-1a/a animal, and Lys-C peptides of this preparation were sequenced. The sequence data were used to direct the synthesis of peptides that were conjugated to albumin and used as immunogens. One of these antisera was specific to meprin-b and thus provided a specific tool to monitor expression of this form of meprin in different mouse strains.

Genetic differences in turnover of glycogen phosphorylase in broiler and layer chickens.

Specific labelling of glycogen phosphorylase with the precursor of the cofactor has allowed definition of the turnover parameters of the enzyme in the pectoralis of rapidly growing broiler chickens, and slowly growing layer chickens. Selection for rapid growth rate in broilers has resulted in a lower rate of turnover of phosphorylase, but the difference between rates of synthesis and degradation is maintained, which contrasts markedly with the age-dependent coalescence of the two values in layer chickens.

Metalloendopeptidase activity in urine of rodents.

The brush border membrane of mice and rats contains a phosphoramidon-insensitive metalloproteinase, meprin (neutral endopeptidase-2; NEP-2). The role of meprin is unknown, but we have shown that urine from these species contains insulin B chain degrading activity that is due to a phosphoramidon-insensitive metalloendopeptidase. By enzymic and immunological criteria, it is likely that this activity is due to meprin, and introduces the possibility that this enzyme may have a role in urinary function.

Proteolytic activity in mouse urine: relationship to the kidney metallo-endopeptidase, meprin.

Meprin, a brush border kidney metallo-endopeptidase is present as the major endopeptidase in mouse urine. The enzyme is freely soluble and can be detected enzymically or immunologically. Mice can be partitioned into two phenotypes that differ by 10-20-fold in the amount of meprin in kidney membranes; this phenotypic variation is reflected in urinary activities. We propose a role for meprin in the degradation of other urinary proteins.

The effect of heat shock on the morphology of amphibian lampbrush chromosomes.

Isolated oocytes of Triturus cristatus carnifex cultured in Barthe's medium respond to a sudden increase in temperature of 35 or 37 degrees C by the rapid condensation of their lampbrush chromosomes. The degree of condensation depends on the severity of the heat shock and is accompanied by the retraction of the transcriptionally active lampbrush loops. The oocytes were kept at 20 degrees C for 12 h after the period of heat shock, before the chromosomes were isolated. The minimum period required to effect loop retraction in immature oocytes of 0.7 mm in diameter was 10 min at 35 degrees C; although more extensive and complete retraction occurred if the oocytes were incubated for periods of up to 40 min. Chromosomes from more mature oocytes (1.4 mm in diameter) require longer periods of heat shock before undergoing condensation. The oocytes themselves do not show any obvious morphological changes after heat shock, although the germinal vesicles are initially too fragile to isolate manually for several hours. When the oocytes are returned to ambient temperatures, they can be cultured in Barthe's medium for several days, enabling the chromosomes to be isolated and studied. Generally, the chromosomes and loops from immature oocytes remain in a condensed state for about 48 h but then the chromosomal axis begins to relax and the loops begin to re-form. Depending on the severity of the initial heat shock, complete recovery of the normal lampbrush morphology is attained after a few days. The re-formed loops are morphologically indistinguishable from untreated loops in control preparations and are of the same length on average. This response of lampbrushes to heat shock is a reliable and repeatable process and should therefore become a valuable model system for the study of chromatin and chromosome structure during changes in transcriptional activity. The time taken for the lampbrushes to recover their normal morphology, is discussed in terms of the return to normal cellular transcription.