Expression of the X-inactivation-associated gene XIST during spermatogenesis.

Mammalian X-chromosome inactivation is thought to be controlled by the X inactivation centre (XIC, X-controlling element -Xce-in mice). A human gene, XIST and its mouse counterpart, Xist, which map to the XIC/Xce, are expressed exclusively from inactive X chromosomes, suggesting their involvement in the process of X-inactivation. We now report the presence of Xist/XIST transcripts in newborn and adult mouse testes, and in human testicular tissue with normal spermatogenesis, but not in the testes of patients who lack germ cells. Our results indicate that while the X chromosome in males is active in somatic cells, it undergoes inactivation during spermatogenesis.

Cloning and expression of the mouse pseudoautosomal steroid sulphatase gene (Sts).

Steroid sulphatase (STS) is an important enzyme in steroid metabolism. The human STS gene has been cloned and mapped to Xp22.3, proximal to the pseudoautosomal region (PAR). Using quantitative differences in STS activity among various mouse strains, a segregation pattern consistent with autosomal linkage was first reported, but more recent studies have linked Sts to the mouse PAR. Failed attempts to clone the mouse Sts gene using human reagants (STS cDNA and anti-STS antibodies) suggest a substantial divergence between these genes. However, partial amino-terminal sequence from purified rat liver Sts is very similar to its human counterpart, and several domains are conserved among all the sulphatases. We followed a degenerate-primer reverse transcriptase-PCR (RT-PCR) approach to amplify a conserved fragment of the rat Sts cDNA that was then used to clone the mouse Sts cDNA. This 2.3-kb cDNA revealed 75% similarity with rat Sts cDNA, while it was only 63% similar to human STS cDNA. Transfection of STS(-) A9 cells with the mouse Sts cDNA restored STS enzymatic activity. Sts was also mapped physically to the distal end of the mouse sex chromosomes, and our backcross studies placed Sts distal to the 'obligatory' cross-over in male meiosis.

A high resolution deletion map of human chromosome Xp22.

We have developed a 32-interval deletion panel for human chromosome Xp22 spanning about 30 megabases of genomic DNA. DNA samples from 50 patients with chromosomal rearrangements involving Xp22 were tested with 60 markers using a polymerase chain reaction strategy. The ensuing deletion map allowed us to confirm and refine the order of previously isolated and newly developed markers. Our mapping panel will provide the framework for mapping new sequences, for orienting chromosome walks in the region and for projects aimed at isolating genes responsible for diseases mapping to Xp22.

The murine Xe169 gene escapes X-inactivation like its human homologue.

Among a number of genes that escape X-chromosome inactivation in humans, three have been evaluated in mice and unexpectedly all three are subject to X-inactivation. We report here the cloning and expression studies of a novel mouse gene, Xe169, and show that it escapes X-inactivation like its human homologue. Xe169 was assigned to band F2/F3 on the mouse X chromosome by fluorescent in situ hybridization and Southern analysis indicates that the gene is located outside the pseudoautosomal region. Homologous, but divergent, sequences exist on the Y chromosome. In vitro and in vivo studies show that Xe169 is expressed from both the active and the inactive X chromosomes. Xe169 is the first cloned non-pseudoautosomal gene that escapes X-inactivation in mice.

Cloning and chromosomal localization of a human kidney cDNA involved in cystine, dibasic, and neutral amino acid transport.

We have recently cloned, sequenced, and characterized a rat kidney cDNA (D2) that stimulates cystine as well as dibasic and neutral amino acid transport. In order to evaluate the role of this protein in human inherited diseases such as cystinuria, we have isolated a human D2 clone (D2H) by low stringency screening of a human kidney cDNA library using the radiolabeled D2 insert as a probe. The D2H cDNA is 2284 nucleotides long and encodes a 663 amino acid protein that is 80% identical to the rat D2 amino acid sequence and 86% to that of the rabbit homologue rBAT. Microinjection of in vitro transcribed D2H cRNA into Xenopus oocytes induced uptake of cystine as well as dibasic and neutral amino acids in a pattern similar to that of rat D2 and rabbit rBAT. Both neutral and dibasic amino acids inhibited the D2H-induced uptake of cystine. Northern blot analysis demonstrated that D2H, like D2 and rBAT, is expressed strongly in the kidney and intestine. Southern blot analysis of genomic DNA from a panel of mouse-human somatic cell hybrids showed that the human gene for D2H resides on chromosome 2.

Assignment of the gene for adrenal P450c17 (steroid 17 alpha-hydroxylase/17,20 lyase) to human chromosome 10.

P450c17 is the single enzyme mediating both 17 alpha-hydroxylase and 17,20 lyase activities. We identified several human P450c17 cDNA clones in a human adrenal cDNA library we constructed in lambda gt10. A short clone containing the 3'-terminal 650 bases of the full-length sequence was used to examine Southern blots of DNA from normal persons and from a panel of mouse/human somatic cell hybrid lines. The pattern of hybridization of this cDNA to normal human DNA cut with 8 restriction endonucleases suggests the human genome has two (or more) P450c17 genes. The pattern of hybridization to the somatic cell hybrid cell lines, each containing a limited, known number of human chromosomes, indicates the human adrenal P450c17 gene lies on chromosome 10. The chromosomal locations of the other P450c17 genes could not be determined.

Chromosome Abnormalities in infants with prune belly anomaly: association with trisomy 18.

Two infants are described with "prune belly anomaly" (PBA) and concomitant trisomy 18. Severe abdominal distention was detected prenatally in one by ultrasonographic study, and in the second child at birth. Other chromosome abnormalities previously associated with PBA also are reviewed. The prune belly anomaly constitutes a malformation sequence that is causally nonspecific and which may occur in diverse aneuploidy syndromes. Aneuploidy is important to detect in prenatally diagnosed cases in which intrauterine fetal treatment is being considered.

Smith-Magenis syndrome resulting from a de novo direct insertion of proximal 17q into 17p11.2.

We report on a de novo intrachromosomal rearrangement of chromosome 17 in a patient with Smith-Magenis syndrome (SMS). This 11-year-old boy had short stature, midfacial hypoplasia, and behavioral problems characteristic of this syndrome. Cytogenetic analysis showed that the proximal long arm of a chromosome 17 (q11.2-q21.3) was inserted into its short arm at p11.2, resulting in an apparent deletion of the SMS critical region [ins(17)(p11.2q11.2q21.3)]. Fluorescence in situ hybridization studies (FISH) demonstrated that the inserted segment included both the ERBB2 and RARA loci, and dual color hybridizations defined the insertion as direct, with ERBB2 located more proximally on the short arm of the der(17). The resulting deletion of the short arm included loci c130G3, D17S258, FLI, and D17S29, while the more proximal loci, D17S446 and D17S58, remained apparently unaffected and in their native locations. The CMT1A locus also remained in its native location on the short arm of the metacentric der(17) chromosome. A de novo intrachromosomal insertional rearrangement of chromosome 17 in a case of SMS has not been reported previously and further illustrates the instability of this chromosomal region.

Maternal disomy and Prader-Willi syndrome consistent with gamete complementation in a case of familial translocation (3;15) (p25;q11.2).

Maternal uniparental disomy (UPD) for chromosome 15 is responsible for an estimated 30% of cases of Prader-Willi syndrome (PWS). We report on an unusual case of maternal disomy 15 in PWS that is most consistent with adjacent-1 segregation of a paternal t(3;15)(p25;q11.2) with simultaneous maternal meiotic nondisjunction for chromosome 15. The patient (J.B.), a 17-year-old white male with PWS, was found to have 47 chromosomes with a supernumerary, paternal der(15) consisting of the short arm and the proximal long arm of chromosome 15, and distal chromosome arm 3p. The t(3;15) was present in the balanced state in the patient's father and a sister. Fluorescent in situ hybridization analysis demonstrated that the PWS critical region resided on the derivative chromosome 3 and that there was no deletion of the PWS region on the normal pair of 15s present in J.B. Methylation analysis at exon alpha of the small nuclear ribonucleoprotein-associated polypeptide N (SNRPN) gene showed a pattern characteristic of only the maternal chromosome 15 in J.B. Maternal disomy was confirmed by polymerase chain reaction analysis of microsatellite repeats at the gamma-aminobutyric acid receptor beta3 subunit (GABRB3) locus. A niece (B.B.) with 45 chromosomes and the derivative 3 but without the der(15) demonstrated a phenotype consistent with that reported for haploinsufficiency of distal 3 p. Uniparental disomy associated with unbalanced segregation of non-Robertsonian translocations has been reported previously but has not, to our knowledge, been observed in a case of PWS. Furthermore, our findings are best interpreted as true gamete complementation resulting in maternal UPD 15 and PWS.

Paternally derived de novo interstitial duplication of proximal 15q in a patient with developmental delay.

Interstitial duplications of proximal 15q containing the Prader-Willi syndrome/Angelman syndrome (PWS/AS) region have been found in patients with autism or atypical autism. In these cases with an abnormal phenotype, the duplications were maternally derived. Paternal origin of the duplication has been associated with a normal phenotype. We report on a patient who presented with nonspecific developmental delay and partial agenesis of the rostral corpus callosum. Fluorescence in situ hybridization (FISH) studies using probes specific for the PWS/AS region demonstrated a double signal on one chromosome 15, indicating the presence of an interstitial duplication of proximal 15q involving the PWS/ AS region in the patient. Parental chromosomes were normal with FISH studies. Methylation analysis at exon alpha of the SNRPN locus showed a maternal band at 4.2 kb and a paternal band of apparent double intensity at 0.9 kb, suggestive of one copy of the maternal allele and two copies of the paternal allele in the patient. Microsatellite analysis was informative at the GABRB3 locus in the family, which showed the inheritance of two different paternal alleles and a maternal allele in the patient consistent with the origin of this duplication from an unequal crossing over between the two chromosome 15 homologs in the father. This is the first report of an abnormal phenotype associated with a paternally derived duplication of proximal 15q shown to contain the PWS/AS region by molecular techniques.

Structure, sequence, chromosomal location, and evolution of the human ferredoxin gene family.

Ferredoxin is an iron-sulfur protein that serves as an electron transport intermediate for mitochondrial cytochromes P450 involved in steroid, vitamin D, and bile acid metabolism. We cloned and characterized the human ferredoxin gene family, which includes two expressed genes and two pseudogenes. Sequence analysis of this gene family revealed that it encodes only one protein product. The expressed genes were assigned to chromosome 11 and pseudogenes to chromosomes 20 and 21 by identifying single-copy probes from each gene segment and hybridizing them to DNA from rodent-human hybrid cells. The pseudogenes lacked introns and contained numerous mutations, including insertion, deletion, and substitution which rendered them inactive. They were 96% and 85% homologous to the expressed gene, yet they were only 78% homologous with each other. The intronless nature, higher diversity among themselves, and distinct chromosomal location of the pseudogenes suggests that they arose by independent, retroposon-mediated events.

Amplification of the MLL region in acute myeloid leukemia.

We report amplification of the MLL gene region (11q23-->11qter) in a 72-year-old woman with myelodysplastic syndrome progressing to acute myelomonocytic leukemia and in a 51-year-old man with a history of hairy cell leukemia and secondary myelodysplasia progressing to acute myelogenous leukemia. The amplicons containing MLL were shown by molecular cytogenetics to extend from chromosomal region 11q23 to the distal long arm of chromosome 11 and to be present in the first patient in five copies on a large ring chromosome and present in the second patient also in five copies on two derived chromosomes. Other karyotypic findings in the first patient included del(5q), +8, and der(21)t(17;21), resulting in the loss of a copy of 17p, whereas deletion 7q was observed in the second patient. Southern-blot analysis for the second patient was consistent with MLL amplification but did not demonstrate rearrangement of the germ-line MLL band. Amplification of MLL and the 11q23 region has been documented in only a few cases and appears to be yet another mechanism by which MLL contributes to the leukemia phenotype.

Diffuse large cell, B-cell type lymphoma with a novel translocation (2;22)(p23;q11.2).

We observed a translocation (2;22)(p23;q11.2) in the bone marrow cells of a patient with multiple subcutaneous nodules. Tumor histology and immunohistochemical staining demonstrated a malignant lymphoma, diffuse large cell type, displaying a CD30 negative B cell immunophenotype. To our knowledge, this is the first report of this specific translocation in lymphoma, which may join the site of the anaplastic lymphoma kinase (ALK) gene at 2p23 to the region of the immunoglobulin lambda light chain gene at 22q11.2. The ALK gene was initially identified through its involvement in the t(2;5)(p23;q35) found most commonly in anaplastic large cell lymphoma. This observation in a CD30 negative large cell lymphoma of B cell lineage further extends the relationship of anaplastic large cell morphology, ALK activation, lymphoid lineage, and expression of the CD30 antigen.

Localization of the Na+/glucose cotransporter gene SGLT2 to human chromosome 16 close to the centromere.

The chromosomal location of the gene SGLT2, which is presumed to encode a low-affinity Na+/glucose cotransporter, has been determined using a panel of rodent-human somatic cell hybrids. Southern blot analysis of genomic DNA from 16 different hybrids shows that SGLT2 is located on chromosome 16. Analysis of three additional hybrids that selectively retain all or part of human chromosome 16 demonstrates that SGLT2 is located close to the centromere in band p11.2 of the chromosome.

Parasexual analysis of human pepsinogen molecular heterogeneity.

Pepsinogens (PGA) are the inactive precursors of pepsin, the major acid protease found in the stomach. Highly polymorphic variation of these proteins has been demonstrated in several populations, and comparison of the DNA restriction fragment patterns obtained from informative pepsinogen phenotypes suggest that the polymorphism results from chromosomal haplotypes containing variable numbers of pepsinogen genes. In order to isolate the three most common PGA haplotypes (A, B, and C) and to unambiguously demonstrate their relationship to the observed protein heterogeneity, we constructed mouse X human somatic cell hybrids from individuals heterozygous for PGA and INS (insulin). Here, we describe analysis of hybrid cell lines that segregated human chromosomes containing the PGA genes and thereby provided for the parasexual discrimination of the different haplotypes on chromosome 11 determining the corresponding heterozygous phenotypes. These studies demonstrate that the A, B, and C haplotypes contain three, two, and one PGA genes, respectively. This unusual polymorphism of genomic DNA encoding very similar proteins probably reflects recent evolution by gene duplication.

Fine mapping of the distal short arm of the human X chromosome using X/Y translocations.

The loci for steroid sulfatase (STS), the deficiency of which causes X-linked ichthyosis, the cell surface antigen 12E7 (MIC2X), and the blood group antigen Xg (Xg) have been mapped to Xp22.3. These loci are of particular interest since they do not appear to undergo X-chromosome inactivation. In an attempt to establish the relative order of STS and MIC2X, fibroblasts from carriers of four different X/Y translocations and an X/10 translocation were obtained and fused with mouse cell lines deficient in hypoxanthine phosphoribosyltransferase. The breakpoints on the X chromosome in these five translocations are in Xp22. Several independent clones from each fusion were isolated in HAT medium. The clones were examined cytogenetically, and in each case at least two independent clones were identified that have an active X/Y or X/10 translocation chromosome in the absence of other X or Y material. These clones were then tested for STS and 12E7 expression. In two of the X/Y translocations, the markers, STS and 12E7, were both absent. In the X/10 and a third X/Y translocation, both markers were retained. In each of three clones containing the fourth X/Y translocation, STS activity was retained but 12E7 antigenicity was lost. Assuming that this is a simple translocation and does not represent a more complex rearrangement, these results suggest that MIC2X is distal to STS.