Deficiency in mouse oxytocin prevents milk ejection, but not fertility or parturition

Oxytocin is a nonapeptide hormone that participates in the regulation of parturition and lactation. It has also been implicated in various behaviors, such as mating and maternal, and memory. To investigate whether or not oxytocin (OT) is essential for any of these functions, we eliminated, by homologous recombination, most of the first intron and the last two exons of the OT gene in mice. Those exons encode the neurophysin portion of the oxytocin preprohormone which is hypothesized to help in the packaging and transport of OT. The homozygous mutant mice have no detectable neurophysin or processed oxytocin in the paraventricular nucleus, supraoptic nucleus or posterior pituitary. Interestingly, homozygous mutant males and females are fertile and the homozygous mutant females are able to deliver their litters. However, the pups do not successfully suckle and die within 24 h without milk in their stomachs. OT injection into the dams restores the milk injection in response to suckling. These results indicate an absolute requirement for oxytocin for successful milk injection, but not for mating, parturition and milk production, in mice.

Structure and organization of the human metaxin gene (MTX) and pseudogene

Metaxin encodes a mitochondrial protein and is an essential nuclear gene in mice. The cDNA sequence and genomic organization of the human metaxin gene (MTX) have now been determined. MTX is 6 kb and consists of eight protein-encoding exons. The gene is contiguous to thrombospondin 3 (THBS3) and to the pseudogene for glucocerebrosidase (psGBA), but it transcribed in a direction opposite to the latter two genes. Thus, MTX and THBS3 share a common promoter region and are transcribed convergently, whereas MTX and psGBA are transcribed convergently and have closed apposed polyadenylation sites. Human metaxin contains 317 amino acids and is 91.5% identical to mouse metaxin. Metaxin is rich in leucine (14.2%) and in basic (12.9%) and acidic (12.0%) amino acids. The predicted protein lacks an amino-terminal signal sequence and N-glycosylation sites, but contains a putative transmembrane domain near its carboxy terminus. A DNA duplication has led to a direct repeat and the evolution of a pseudogene for GBA. A pseudogene for metaxin (psMTX) is also located within the 16 kb of DNA separating GBA from psGBA. The psMTX sequence is nearly identical to the 3' part of exon 2 through exon 8 of MTX, and both the intronic and the 3'-flanking sequences are highly conserved. Thus, there is a 278 amino acid open reading frame that is 97.8% identical to metaxin. However, psMTX lacks the first intron and promoter present in MTX, and at least in liver, the pseudogene is not expressed.

Genotype D399N/R463C in a patient with type 3 Gaucher disease previously assigned genotype N370S/R463C

A patient with type 3 Gaucher disease is described with a novel genotype, D399N/R463C, established by DNA sequencing. This patient was previously reported as having genotype N370S/R463C. This communication now establishes that no patients reported with mutation N370S have the neuronopathic forms of Gaucher disease and has important implications for genetic counseling.

A genome-wide search for chromosomal loci linked to bipolar affective disorder in the Old Order Amish

The most characteristic features of bipolar affective disorder (manic-depressive illness) are episodes of mania (bipolar I, BPI) or hypomania (bipolar II, BPII) interspersed with periods of depression. Manic-depressive illness afflicts about one percent of the population, and if untreated, is associated with an approximately 20% risk of suicide. Twin, family and adoption studies provide compelling evidence for a partial genetic aetiology, but the mode(s) of inheritance has not been identified. Nonetheless, the majority of genetic linkage studies have assumed classical mendelian inheritance attributable to a single major gene. Although segregation analyses have yielded inconsistent results (with most studies rejecting a single locus inheritance model), the best single gene model is dominant inheritance if only BPI is considered. Reported linkages of bipolar affective disorder on chromosomes 11, 18, 21 and X have been difficult to substantiate, and additional studies are required for replication or exclusion of these regions. We now present the results of our genome-wide linkage analyses that provide evidence that regions on chromosomes 6, 13 and 15 harbour susceptibility loci for bipolar affective disorder, suggesting that bipolar affective disorder in the Old Order Amish is inherited as a complex trait.

Epidermal abnormalities may distinguish type 2 from type 1 and type 3 of Gaucher disease

A major clinical challenge in Gaucher disease is the early and presymptomatic discrimination of type 2 (acute neuronopathic) from milder type 1 and type 3 Gaucher patients to enable appropriate management and counseling. Although most patients with Gaucher disease do not have skin abnormalities, a subset of patients with severe type 2 Gaucher disease display ichthyosiform skin. Analogous findings occur in the skin of type 2 (null allele) Gaucher mice. Ultrastructural and functional studies of epidermis from these mice reveal that glucocerebrosidase is required to generate functionally competent membranes for normal epidermal barrier function. We have extended our studies by examining the epidermal lipid content and ultrastructure in all three types of Gaucher patients. Only the type 2 Gaucher patients, some of whom had clinical ichthyosis, demonstrated an increased ratio of epidermal glucosylceramide to ceramide as well as extensive ultrastructural abnormalities, including the persistence of incompletely processed lamellar body-derived contents throughout the stratum corneum interstices. These epidermal alterations may provide a means for early differentiation of type 2 Gaucher disease.

A biochemical and immunocytochemical study on the targeting of alglucerase in murine liver

A current hypothesis is that functional glucocerebrosidase needs to be delivered to the lysosomes of tissue macrophages to guarantee successful enzyme therapy for Gaucher's disease. In this study, biochemical and immunohistochemical techniques were applied to identify in mice the localization of intravenously administered alglucerase (human modified placental glucocerebrosidase). Only in liver and spleen was a significant increase of glucocerebrosidase activity observed, with a maximum level at 15 minutes after enzyme infusion. The uptake of enzyme by liver was sufficiently high to allow more detailed studies on the (sub)cellular distribution of human alglucerase. The enzyme in liver is localized both in the endosomal-lysosomal system of the Kupffer cells and the endothelial cells lining the lumen of the sinusoids. Uptake by both of these types of cell is prevented by mannan. The results suggest that the cellular mechanisms responsible for improvement of Gaucher patients receiving alglucerase treatment is probably more complicated than previously recognized.

Diagnosing Gaucher disease. Early recognition, implications for treatment, and genetic counseling

The diagnosis of Gaucher disease, the inherited deficiency of glucocerebrosidase and the most common inherited disorder of Ashkenazi Jews, can often be missed by clinicians. Medical records from patients with Gaucher disease were reviewed, revealing a wide range of initial misdiagnoses and the frequent use of unnecessary invasive diagnostic procedures. The diagnosis of Gaucher disease is readily established by enzymatic or DNA analyses in conjunction with a thorough history and physical examination. Consequently, greater awareness of the symptoms encountered in these patients could alleviate unnecessary anxiety, testing, and confusion. A definitive diagnosis of Gaucher disease has important implications for genetic counseling and treatment.

Structure and organization of the human thrombospondin 3 gene (THBS3)

The promoter/5' flank sequence, cDNA sequence, and exon/intron structures of the human thrombospondin 3 (THBS3) gene have been determined. THBS3 cDNA clones were obtained by PCR amplification of human fetal lung cDNA using THBS3-specific primers. Analysis of cDNA and genomic sequences showed the THBS3 gene to be composed of 23 exons, 1 more than the number of exons in the previously characterized mouse TSP3 gene. The additional exon results from the division of mouse exon F into exons F1 and F2. The cDNA encodes a polypeptide of 956 amino acids that is highly acidic, with a clustering of acidic side chains in the third quarter of the polypeptide. This region corresponds to seven type III (Ca(2+)-binding) repeats, a feature shared with other thrombospondins. In addition to these type III repeats, four type II (EGF-like) repeats and NH2- and COOH-terminal domains are present in thrombospondin 3. The THBS3 and mouse TSP3 genes differ in intron sizes, but exon sequences and sizes and positions of insertion of introns are conserved to a high degree. The structural organization of the THBS3 gene is of interest because of its close proximity to that of metaxin, with which it shares a common promoter sequence, and to the gene encoding glucocerebrosidase, a deficiency in which causes Gaucher disease.

Metaxin, a gene contiguous to both thrombospondin 3 and glucocerebrosidase, is required for embryonic development in the mouse: implications for Gaucher disease

We have identified a murine gene, metaxin, that spans the 6-kb interval separating the glucocerebrosidase gene (GC) from the thrombospondin 3 gene on chromosome 3E3-F1. Metaxin and GC are transcribed convergently; their major polyadenylylation sites are only 431 bp apart. On the other hand, metaxin and the thrombospondin 3 gene are transcribed divergently and share a common promoter sequence. The cDNA for metaxin encodes a 317-aa protein, without either a signal sequence or consensus for N-linked glycosylation. Metaxin protein is expressed ubiquitously in tissues of the young adult mouse, but no close homologues have been found in the DNA or protein data bases. A targeted mutation (A-->G in exon 9) was introduced into GC by homologous recombination in embryonic stem cells to establish a mouse model for a mild form of Gaucher disease. A phosphoglycerate kinase-neomycin gene cassette was also inserted into the 3'-flanking region of GC as a selectable marker, at a site later identified as the terminal exon of metaxin. Mice homozygous for the combined mutations die early in gestation. Since the same amino acid mutation in humans is associated with mild type 1 Gaucher disease, we suggest that metaxin protein is likely to be essential for embryonic development in mice. Clearly, the contiguous gene organization at this locus limits targeting strategies for the production of murine models of Gaucher disease.

Consequences of beta-glucocerebrosidase deficiency in epidermis. Ultrastructure and permeability barrier alterations in Gaucher disease

Hydrolysis of glucosylceramide by beta-glucocerebrosidase results in ceramide, a critical component of the intercellular lamellae that mediate the epidermal permeability barrier. A subset of type 2 Gaucher patients displays ichthyosiform skin abnormalities, as do transgenic Gaucher mice homozygous for a null allele. To investigate the relationship between glucocerebrosidase deficiency and epidermal permeability barrier function, we compared the stratum corneum (SC) ultrastructure, lipid content, and barrier function of Gaucher mice to carrier and normal mice, and to hairless mice treated topically with bromoconduritol B epoxide (BrCBE), an irreversible inhibitor of glucocerebrosidase. Both Gaucher mice and BrCBE-treated mice revealed abnormal, incompletely processed, lamellar body-derived sheets throughout the SC interstices, while transgenic carrier mice displayed normal bilayers. The SC of a severely affected type 2 Gaucher's disease infant revealed similarly abnormal ultrastructure. Furthermore, the Gaucher mice demonstrated markedly elevated transepidermal water loss (4.2 +/- 0.6 vs < 0.10 g/m2 per h). The electron-dense tracer, colloidal lanthanum, percolated between the incompletely processed lamellar body-derived sheets in the SC interstices of Gaucher mice only, demonstrating altered permeability barrier function. Gaucher and BrCBE-treated mice showed < 1% and < 5% of normal epidermal glucocerebrosidase activity, respectively, and the epidermis/SC of Gaucher mice demonstrated elevated glucosylceramide (5- to 10-fold), with diminished ceramide content. Thus, the skin changes observed in Gaucher mice and infants may result from the formation of incompetent intercellular lamellar bilayers due to a decreased hydrolysis of glucosylceramide to ceramide. Glucocerebrosidase therefore appears necessary for the generation of membranes of sufficient functional competence for epidermal barrier function.

DNA mutational analysis of type 1 and type 3 Gaucher patients: how well do mutations predict phenotype?

The wide spectrum of clinical manifestations resulting from glucocerebrosidase deficiency complicates genetic counseling for Gaucher disease. The identification of mutations in the glucocerebrosidase gene has enabled studies of genotype-phenotype correlation. However, a genotypic analysis of 60 type 1 and type 3 Gaucher patients reveals that the 5 most common Gaucher mutations, N370S, L444P, R463C, 84insG, and IVS2 + 1 G-->A, can be found both in patients with and without neurologic manifestations. Moreover, although some generalizations can be made about mutations that are more frequently encountered in particular patient populations, Gaucher patients sharing identical genotypes can exhibit considerable clinical heterogeneity. Thus in considering rationale for population screening one cannot rely solely on PCR determined DNA mutation analysis to reliably predict prognosis in Gaucher disease.

A novel transcript from a pseudogene for human glucocerebrosidase in non-Gaucher disease cells

Human glucocerebrosidase (GC)-encoding cDNA clones were isolated from a promyelocytic HL-60 cDNA library and analyzed. A novel cDNA clone was found to originate from a gene referred to as a GC pseudogene. Using the polymerase chain reaction (PCR) with primers specific for the GC pseudogene, we found that all the human cell lines examined, HL-60, K-562, WI-38, HepG2 and HeLa, expressed a pseudogene transcript. In vitro translation of RNA synthesized by transcription of the pseudogene cDNA produced a polypeptide of approximately 30 kDa.

Isolation, characterization, and proteolysis of human prosaposin, the precursor of saposins (sphingolipid activator proteins)

Prosaposin contains separate domains in tandem for four saposins, A, B, C, and D. These mature saposins are produced by limited proteolysis of prosaposin. They are involved in lysosomal hydrolysis of GM1 ganglioside, gluco- and galactocerebrosides, sulfatides, and sphingomyelin and other sphingolipids. Prosaposin also exists as a secretory protein in body fluids. In this investigation prosaposin was expressed in Spodoptera frugiperda cells (Sf9) by infection with baculovirus containing a full length cDNA coding for human prosaposin. Prosaposin was isolated and purified from spent culture medium of the recombinant Sf9 cell cultures as well as from human seminal plasma and milk. From sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the molecular weight of both native human prosaposins is estimated to be 66 kDa and that of recombinant prosaposin as 58 kDa. Deglycosylation of native and recombinant prosaposins yielded a protein with a molecular weight of 54 kDa and isoelectric point of 5.4. The N-terminal sequence of both native and recombinant prosaposins was identical (G-P-V-L-L-G-L-K). Like mature saposins, all prosaposins possessed stimulative activity for cerebroside beta-glucosidase (saposins A and C activity), GM1 ganglioside beta-galactosidase (saposin B activity), and sphingomyelinase (saposin D activity) but not sulfatide sulfatase (saposin B activity). Partially proteolyzed products derived from prosaposins were isolated and identified. From seminal plasma, two proteins of 48 and 29 kDa and from Sf9 culture media, two proteins of 39 and 26 kDa were characterized. N-terminal amino acid sequencing and Western blot analysis of each protein indicated that the 39-and 48-kDa proteins are cleavage products containing domains for saposins B, C, and D (trisaposins), and the 26- and 29-kDa proteins are cleavage products containing domains for saposins C and D (disaposin). These observations suggest that proteolysis of prosaposin in these tissues occurs sequentially from the N-terminal region. Proteins involved in the initial proteolysis of prosaposin were partially characterized in human testis.

Gaucher disease in the neonate: a distinct Gaucher phenotype is analogous to a mouse model created by targeted disruption of the glucocerebrosidase gene

A group of neonates with Gaucher disease with a particularly devastating clinical course is described. The phenotype of these infants is analogous to that of a Gaucher mouse, which was created by targeted disruption of the mouse glucocerebroside gene. Similar to the homozygous mutant mice with glucocerebrosidase deficiency, these infants present at or shortly after birth, have rapidly progressing fulminant disease, and many have associated ichthyotic skin and/or hydrops fetalis. This transgenetic mouse model of Gaucher disease has helped us to appreciate a distinct Gaucher phenotype. Potentially, as this technology is applied to create other animal models of metabolic diseases, it may enable the recognition of other, as yet unappreciated presentations of inherited disorders.

Update on the search for DNA markers linked to manic-depressive illness in the Old Order Amish

In this report we describe our efforts to identify a gene involved in bipolar illness using a large, multigenerational Old Order Amish pedigree with many affected individuals. The original collection of cell lines from Amish pedigree 110 has been extended to include 169 individuals. We have used over 250 markers spaced at approximately 20 centiMorgans that detect restriction length fragment polymorphisms, but no LOD scores greater than 3 have been obtained from pairwise linkage analyses. We are expanding our collection of cell lines from both normal and affected family members and updating our diagnostic data as we continue our systematic screening of the genome for a gene involved in bipolar illness.