Xylosyltransferase 2 deficiency and organ homeostasis

In this paper we characterize the function of Xylosyltransferase 2 (XylT2) in different tissues to investigate the role XylT2 has in the proteoglycan (PG) biochemistry of multiple organs. The results show that in all organs examined there is a widespread and significant decrease in total XylT activity in Xylt2 knock out mice (Xylt2-/-). This decrease results in increased organ weight differences in lung, heart, and spleen. These findings, in addition to our previous findings of increased liver and kidney weight with loss of serum XylT activity, suggest systemic changes in organ function due to loss of XylT2 activity. The Xylt2-/- mice have splenomegaly due to enlargement of the red pulp area and enhanced pulmonary response to bacterial liposaccharide. Tissue glycosaminoglycan composition changes are also found. These results demonstrate a role of XylT2 activity in multiple organs and their PG content. Because the residual XylT activity in the Xylt2-/- is due to xylosyltransferase 1 (XylT1), these studies indicate that both XylT1 and XylT2 have important roles in PG biosynthesis and organ homeostasis.

Adipose tissue loss and lipodystrophy in xylosyltransferase II deficient mice

BACKGROUND/OBJECTIVES

The cellular and extracellular matrix (ECM) interactions that regulate adipose tissue homeostasis are incompletely understood. Proteoglycans (PGs) and their sulfated glycosaminoglycans (GAGs) provide spatial and temporal signals for ECM organization and interactions with resident cells by impacting growth factor and cytokine activity. Therefore, PGs and their GAGs could be significant to adipose tissue homeostasis. The purpose of this study was to determine the role of ECM sulfated GAGs in adipose tissue homeostasis.

METHODS

Adipose tissue and metabolic homeostasis in mice deficient in xylosyltransferase 2 (Xylt2-/-) were examined by histologic analyses, gene expression analyses, whole body fat composition measurements, and glucose tolerance test. Adipose tissue inflammation and adipocyte precursors were characterized by flow cytometry and in vitro culture of mesenchymal stem cells.

RESULTS

Xylt2-/- mice have low body weight due to overall reductions in abdominal fat deposition. Histologically, the adipocytes are reduced in size and number in both gonadal and mesenteric fat depots of Xylt2-/- mice. In addition, these mice are glucose intolerant, insulin resistant, and have increased serum triglycerides as compared to Xylt2 + / + control mice. Furthermore, the adipose tissue niche has increased inflammatory cells and enrichment of proinflammatory factors IL6 and IL1β, and these mice also have a loss of adipose tissue vascular endothelial cells. Lastly, xylosyltransferease-2 (XylT2) deficient mesenchymal stem cells from gonadal adipose tissue and bone marrow exhibit impaired adipogenic differentiation in vitro.

CONCLUSIONS

Decreased GAGs due to the loss of the key GAG assembly enzyme XylT2 causes reduced steady state adipose tissue stores leading to a unique lipodystrophic model. Accumulation of an adipocytic precursor pool of cells is discovered indicating an interruption in differentiation. Therefore, adipose tissue GAGs are important in the homeostasis of adipose tissue by mediating control of adipose precursor development, tissue inflammation, and vascular development.

Homozygosity for frameshift mutations in XYLT2 result in a spondylo-ocular syndrome with bone fragility, cataracts, and hearing defects

Heparan and chondroitin/dermatan sulfated proteoglycans have a wide range of roles in cellular and tissue homeostasis including growth factor function, morphogen gradient formation, and co-receptor activity. Proteoglycan assembly initiates with a xylose monosaccharide covalently attached by either xylosyltransferase I or II. Three individuals from two families were found that exhibited similar phenotypes. The index case subjects were two brothers, individuals 1 and 2, who presented with osteoporosis, cataracts, sensorineural hearing loss, and mild learning defects. Whole exome sequence analyses showed that both individuals had a homozygous c.692dup mutation (GenBank: NM_022167.3) in the xylosyltransferase II locus (XYLT2) (MIM: 608125), causing reduced XYLT2 mRNA and low circulating xylosyltransferase (XylT) activity. In an unrelated boy (individual 3) from the second family, we noted low serum XylT activity. Sanger sequencing of XYLT2 in this individual revealed a c.520del mutation in exon 2 that resulted in a frameshift and premature stop codon (p.Ala174Profs(∗)35). Fibroblasts from individuals 1 and 2 showed a range of defects including reduced XylT activity, GAG incorporation of (35)SO4, and heparan sulfate proteoglycan assembly. These studies demonstrate that human XylT2 deficiency results in vertebral compression fractures, sensorineural hearing loss, eye defects, and heart defects, a phenotype that is similar to the autosomal-recessive disorder spondylo-ocular syndrome of unknown cause. This phenotype is different from what has been reported in individuals with other linker enzyme deficiencies. These studies illustrate that the cells of the lens, retina, heart muscle, inner ear, and bone are dependent on XylT2 for proteoglycan assembly in humans.

Xylosyltransferase II is a significant contributor of circulating xylosyltransferase levels and platelets constitute an important source of xylosyltransferase in serum

Circulating glycosyltransferases including xylosyltransferases I (XylT1) and II (XylT2) are potential serum biomarkers for various diseases. Understanding what influences the serum activity of these enzymes as well as the sources of these enzymes is important to interpreting the significance of alterations in enzyme activity during disease. This article demonstrates that in the mouse and human the predominant XylT in serum is XylT2. Furthermore, that total XylT levels in human serum are approximately 200% higher than those in plasma due in part to XylT released by platelets during blood clotting in vitro. In addition, the data from Xylt2 knock-out mice and mice with liver neoplasia show that liver is a significant source of serum XylT2 activity. The data presented suggest that serum XylT levels may be an informative biomarker in patients who suffer from diseases affecting platelet and/or liver homeostasis.

Polycystic disease caused by deficiency in xylosyltransferase 2, an initiating enzyme of glycosaminoglycan biosynthesis

The basic biochemical mechanisms underlying many heritable human polycystic diseases are unknown despite evidence that most cases are caused by mutations in members of several protein families, the most prominent being the polycystin gene family, whose products are found on the primary cilia, or due to mutations in posttranslational processing and transport. Inherited polycystic kidney disease, the most prevalent polycystic disease, currently affects approximately 500,000 people in the United States. Decreases in proteoglycans (PGs) have been found in tissues and cultured cells from patients who suffer from autosomal dominant polycystic kidney disease, and this PG decrease has been hypothesized to be responsible for cystogenesis. This is possible because alterations in PG concentrations would be predicted to disrupt many homeostatic mechanisms of growth, development, and metabolism. To test this hypothesis, we have generated mice lacking xylosyltransferase 2 (XylT2), an enzyme involved in PG biosynthesis. Here we show that inactivation of XylT2 results in a substantial reduction in PGs and a phenotype characteristic of many aspects of polycystic liver and kidney disease, including biliary epithelial cysts, renal tubule dilation, organ fibrosis, and basement membrane abnormalities. Our findings demonstrate that alterations in PG concentrations can occur due to loss of XylT2, and that reduced PGs can induce cyst development.

Biosynthesis of chondroitin and heparan sulfate in chinese hamster ovary cells depends on xylosyltransferase II

Xylosyltransferase (XylT) catalyzes the initial enzymatic reaction in the glycosaminoglycan assembly pathway for proteoglycan biosynthesis. Its activity is thought to be rate-limiting. Two xylosyltransferases have been found using genomic analyses, and one of these, XylT1, has been shown to have xylosyltransferase activity. On the other hand, the less studied XylT2 in recombinant form lacks xylosyltransferase activity and has no known function. Wild-type Chinese hamster ovary cells express abundant Xylt2 mRNA levels and lack detectable Xylt1 mRNA levels. Analysis of a previously described Chinese hamster ovary cell xylosyltransferase mutant (psgA-745) shows that it harbors an Xylt2 nonsense mutation and fails to assemble glycosaminoglycans onto recombinant biglycan. Transfection of this cell line with a murine Xylt2 minigene results in the production of recombinant chondroitin sulfate-modified biglycan core protein and restoration of fibroblast growth factor binding to cell surface-associated heparan sulfate. Expression analyses on 10 different human transformed cell lines detect exclusive XYLT2 expression in two and co-expression of XYLT1 and XYLT2 in the others but at disparate ratios where XYLT2 expression is greater than XYLT1 in most cell lines. These results indicate that XylT2 has a significant role in proteoglycan biosynthesis and that cell type may control which family member is utilized.

Complex control of mouse apolipoprotein B gene expression revealed by targeted duplication

An elevated plasma level of apolipoprotein B-containing lipoproteins is a risk factor for atherosclerotic cardiovascular disease. Subtle genetic abnormalities in gene expression including an increased expression of the APOB gene may play an important role in determining overall risk. In an attempt to increase mouse Apob expression, we used gene targeting and duplicated approximately 65 kb of genomic DNA containing the Apob locus in its natural genomic position in mice. While we successfully generated mice carrying the Apob gene duplication, the amount of the total Apob mRNA was not increased in their liver. In the intestine, total Apob mRNA was reduced to half of the wild-type mice. Plasma lipids in the Apob duplication mice were not altered. Expression analyses showed that the proximal Apob gene in the duplicated locus was preferentially expressed in both tissues suggesting a limitation of tissue-specific enhancer function. The previously characterized distant intestinal control element was not duplicated, explaining the unequal ratio of intestinal Apob expression. While the existence of an additional liver-specific enhancer element is unknown, our findings suggest the presence of an additional enhancer outside the duplicated region, and that Apob gene expression is more complicated than previously thought.

ApoB-48 and apoB-100 differentially influence the expression of type-III hyperlipoproteinemia in APOE*2 mice

Apolipoprotein E (apoE) is essential for the clearance of plasma chylomicron and VLDL remnants. The human APOE locus is polymorphic and 5-10% of APOE*2 homozygotes exhibit type-III hyperlipoproteinemia (THL), while the remaining homozygotes have less than normal plasma cholesterol. In contrast, mice expressing APOE*2 in place of the mouse Apoe (Apoe(2/2) mice) are markedly hyperlipoproteinemic, suggesting a species difference in lipid metabolism (e.g., editing of apolipoprotein B) enhances THL development. Since apoB-100 has an LDLR binding site absent in apoB-48, we hypothesized that the Apoe(2/2) THL phenotype would improve if all Apoe(2/2) VLDL contained apoB-100. To test this, we crossed Apoe(2/2) mice with mice lacking the editing enzyme for apoB (Apobec(-/-)). Consistent with an increase in remnant clearance, Apoe(2/2). Apobec(-/-) mice have a significant reduction in IDL/LDL cholesterol (IDL/LDL-C) compared with Apoe(2/2) mice. However, Apoe(2/2).Apobec(-/-) mice have twice as much VLDL triglyceride as Apoe(2/2) mice. In vitro tests show the apoB-100-containing VLDL are poorer substrates for lipoprotein lipase than apoB-48-containing VLDL. Thus, despite a lowering in IDL/LDL-C, substituting apoB-48 lipoproteins with apoB-100 lipoproteins did not improve the THL phenotype in the Apoe(2/2).Apobec(-/-) mice, because apoB-48 and apoB-100 differentially influence the catabolism of lipoproteins.

Analysis of glutathione by capillary electrophoresis based on sample stacking

Glutathione is a small peptide, which participates in cellular oxidation-reduction and detoxification. It is present in most biological tissues at different concentrations. The oxidized and reduced forms of the peptide were measured in erythrocytes and myocardial tissue by capillary electrophoresis based on stacking. After tissue homogenization or hemolysis of the red blood cells, the samples were deproteinized with acetonitrile and injected filling about 13% of the capillary volume. The electrophoresis was performed at 10 kV using a separation buffer of 250 mM borate, 50 mM Tris, pH 8.0. Sample stacking increased the sensitivity of detection by 10-20-fold.

Lessons learned from the mouse model of short-chain acyl-CoA dehydrogenase deficiency

The SCAD deficient mouse model has been useful to investigate mechanisms of deficient fatty acid oxidation disease in human patients. This mouse model has been thoroughly characterized and is readily available from the Jackson Laboratory. Using the new technologies of gene-knockout mouse modeling, we envisage developing additional members of the acyl-CoA dehydrogenase family of enzyme deficiencies in mice and furthering our understanding of fatty acid metabolism in health and disease.

Hemoglobin A2 quantification by capillary zone electrophoresis

Hemoglobin A2 (HbA2) comprises about 2.2% of the total hemoglobin in the erythrocytes. The separation and quantitation of this minor hemoglobin by capillary electrophoresis (CE) using an arginine Tris buffer is described. Some of the variables affecting the accuracy and precision of HbA2 quantification are investigated. Furthermore, the quantification of this hemoglobin by CE is compared to that of a microcolumn chromatography method. The CE method is better suited than the microcolumn method for measuring HbA2 in the sickle cell trait.

Regulation of the apolipoprotein B in heterozygous hypobetalipoproteinemic knock-out mice expressing truncated apoB, B81. Low production and enhanced clearance of apoB cause low levels of apoB

Low levels of cholesterol are protective against development of coronary artery disease. Heterozygous hypobetalipoproteinemic individuals expressing truncated apolipoprotein (apo)B as a result of mutation in the apob gene have low levels of cholesterol and apoB in their plasma. To study the molecular mechanism of low levels of apoB in these individuals, we employed a previously reported knock out mouse model generated by targeted modification of the apob gene. The heterozygous, apoB-100/B-81, mice express full length and truncated apoB, B-81, and have 20 and 35% lower levels of total cholesterol and apoB, respectively, when compared to WT (apoB-100/B-100) mice. The majority of the truncated apoB, B-81, fractionated in the VLDL- density range. The mechanism of low levels of apoB in B-100/B-81 mice was examined. Total hepatic apoB mRNA levels decreased by 15%, primarily due to lower levels of apoB-81 mRNA. Since apoB mRNA transcription rates were similar in B-100/B-100 and B-100/B-81 mice, low levels of mutant apoB-81 mRNA occurred by enhanced degradation of apoB mRNA transcript containing premature translational stop codon. ApoB synthesis measured on isolated hepatocytes decreased in B-100/B-81 mice by 35%, while apoB-48, apoE, and apoAI syntheses remained unchanged. Metabolic studies using whole animal showed a 32% decrease in triglyceride secretion rates, consistent with the apoB secretion rates. Inhibition of receptor-mediated clearance of apoB-81-containing particles resulted in greater relative accumulation of apoB-81 in plasma than apoB-100, suggesting enhanced clearance of apoB-81-containing particles. These results demonstrate that low levels of apoB in heterozygous hypobetalipoproteinemic mice occurs by low rates of apoB secretion, and increased clearance of truncated apoB. Similar mechanisms appear to contribute to low levels of apoB in hypobetalipoproteinemic humans.

Apo E structure determines VLDL clearance and atherosclerosis risk in mice

We have generated mice expressing the human apo E4 isoform in place of the endogenous murine apo E protein and have compared them with mice expressing the human apo E3 isoform. Plasma lipid and apolipoprotein levels in the mice expressing only the apo E4 isoform (4/4) did not differ significantly from those in mice with the apo E3 isoform (3/3) on chow and were equally elevated in response to increased lipid and cholesterol in their diet. However, on all diets tested, the 4/4 mice had approximately twice the amount of cholesterol, apo E, and apo B-48 in their VLDL as did 3/3 mice. The 4/4 VLDL competed with human LDL for binding to the human LDL receptor slightly better than 3/3 VLDL, but the VLDL clearance rate in 4/4 mice was half that in 3/3 mice. On an atherogenic diet, there was a trend toward greater atherosclerotic plaque size in 4/4 mice compared with 3/3 mice. These data, together with our earlier observations in wild-type and human APOE*2-replacement mice, demonstrate a direct and highly significant correlation between VLDL clearance rate and mean atherosclerotic plaque size. Therefore, differences solely in apo E protein structure are sufficient to cause alterations in VLDL residence time and atherosclerosis risk in mice.

Limb, genital, CNS, and facial malformations result from gene/environment-induced cholesterol deficiency: further evidence for a link to sonic hedgehog

Low cholesterol levels produced by treating cholesterol deficient mutant mice with a cholesterol synthesis inhibitor (BM 15.766) between days 4 to 7 of pregnancy resulted in malformations consistent with those in the Smith-Lemli-Opitz syndrome (SLOS). Facial anomalies in mildly affected gestational day 12 mouse embryos included a small nose and long upper lip; in more severely affected embryos, the facial and forebrain anomalies are representative of holoprosencephaly. Additionally, abnormalities of the mid- and hind-brain were observed and included stenosis of the cerebral aqueduct at the level of the isthmus and apparent absence of the organ progenitor for the cerebellar vermis. Although not previously directly linked to cholesterol deficiency in experimental animals, limb and external genital defects were a notable outcome in this multifactorially-based cholesterol deficiency model. The results of this study provide new evidence supporting an important role for cholesterol in early embryonic development, provide additional support for the hypothesis that this role may involve the function of specific gene products, such as sonic hedgehog (shh) signaling protein, and provide a description of the pathogenesis of some of the characteristic malformations in SLOS.

Analysis of nitrate in biological fluids by capillary electrophoresis

Nitrite and nitrate represent the products of the final pathway of nitric oxide metabolism. These two ions were analyzed by capillary electrophoresis (CE) in serum, cerebrospinal fluid, urine and tissue homogenates by mixing the sample with acetonitrile containing NaBr as an internal standard, followed by centrifugation. The supernatant was injected hydrodynamically on a capillary 50 cm x 75 microns (I.D.) and electrophoresed at 6 kV (reversed polarity) in 1.4% sodium chloride in phosphate buffer for 13 min with detection at 214 nm. In addition to removal of the proteins, acetonitrile caused sample stacking. Urinary nitrate analysis by CE was compared to that by the enzymatic Aspergillus nitrate reductase method, with a correlation coefficient of 0.96.

Analysis of ibuprofen in serum by capillary electrophoresis

A rapid method for analysis of the analgesic drug ibuprofen in serum by capillary zone electrophoresis in a borate buffer 160 mmol/l pH 8.5 is described. The method involves deproteinization with acetonitrile to remove serum proteins followed by direct injection on the capillary. The recoveries of standards added to the serum were 84-92%. The method is suited for analysis of samples with concentrations > 10 mg/l. Many other analgesics such as ketoprofen, daypro and salicylates can also be determined by this method.

Structure and chromosomal location of the mouse medium-chain acyl-CoA dehydrogenase-encoding gene and its promoter

Medium-chain acyl-coenzyme A dehydrogenase (MCAD; mouse gene Acadm; human gene ACADM) catalyzes the initial step of fatty acid beta-oxidation in mitochondria. Inherited MCAD deficiency is an autosomal recessive disorder that occurs at high frequency in humans and is associated with considerable morbidity and mortality. We have cloned and characterized mouse Acadm which spans approximately 25 kb and contains 12 exons. The promoter region does not contain TATA or CAAT boxes and is G + C-rich (60%) within 200 bp of the cap site. A CpG island extends from 5' of the transcription start point into intron 1. The 5' regulatory region and a portion of intron 1 contain several Sp1 consensus sites and three regions containing hexamer DNA sequences that match the binding consensus for steroid/thyroid nuclear receptors. These putative nuclear receptor response elements (NRRE) share DNA sequence homology and electrophoretic mobility shift characteristics with known NRRE in the human ACADM promoter [Carter et al., J. Biol. Chem. 268 (1993) 13805-13810]. We have mapped mouse Acadm to the distal end of chromosome 3. Sequences previously localized to chromosome 8 are shown to be a pseudogene, and an additional pseudogene was identified on chromosome 11.

Effects of short-chain acyl-CoA dehydrogenase deficiency on development expression of metabolic enzyme genes in the mouse

Patients with an acyl-CoA dehydrogenase deficiency share the disease features of hypoglycemia, hyperammonemia, tissue fatty change, hypoketonemia, carnitine deficiency, and organic acidemia due to apparent disruption of normal fatty acid, glucose, and urea metabolism. Most of the acute clinical episodes occur in young children. These episodes are precipitated by fasting and are often fatal, with the in vivo mechanisms essentially unknown. Since the genes of the rate controlling enzymes of these pathways are tissue and developmentally regulated at the transcriptional level, we measured, throughout neonatal development, the steady-state mRNA levels of long-chain, medium-chain, and short-chain (SCAD) acyl-CoA dehydrogenases, pyruvate carboxylase (PC), phosphoenolpyruvate carboxykinase (PEPCK), carbamyl phosphate synthetase I (CPS), ornithine transcarbamylase (OTC), and argininosuccinate synthetase (AS) in fed or fasted SCAD-deficient BALB/ByJ mice compared to BALB/cBy controls. Overall, our results showed no major effects on expression of acyl-CoA dehydrogenases due to SCAD deficiency, regardless of age or fasting. In SCAD-deficient mice we found depressed mRNA expression and enzyme activity for the urea cycle enzymes CPS and AS at 6 days of age, and found no apparent effects on expression of gluconeogenic enzymes PC or PEPCK. There was a period of overall lower gene expression for most genes at 6 and 15 days, which appears to be in parallel with the developmental period when children with these diseases are most severely affected.

Some variables affecting reproducibility in capillary electrophoresis

Several variables that can affect reproducibility of both the peak height and the migration time in capillary electrophoresis (CE) were investigated here. A great part of the imprecision in CE for migration time is related to the interaction of the analyte with the capillary wall. Within a run, acidic compounds with long migration times have a higher relative standard deviation. In general, conditions that decreased the migration time, such as a short capillary length, tended to enhance the reproducibility of the migration time. Sample size also affected the reproducibility of peak height. Too small or too large an injection volume diminished the reproducibility. Sample matrix, such as high levels of proteins or salts in the sample, decreased the reproducibility. Furthermore, improvement in reproducibility can be achieved by using internal standards (especially for migration time), thorough washing of the capillary, or removing the excess proteins by acetonitrile deproteinization. Acetonitrile has an added effect of producing sample stacking. Depending on the migration time and analyte concentration, the peak height and area yielded different reproduciblity results.

RNA expression and chromosomal location of the mouse long-chain acyl-CoA dehydrogenase gene

The cDNA for mouse long-chain acyl-CoA dehydrogenase (Acadl, gene symbol; LCAD, enzyme) was cloned and characterized. The cDNA was obtained by library screening and reverse transcription-polymerase chain reaction (RT-PCR). The deduced amino acid sequence showed a high degree of homology to both the rat and the human LCAD sequence. Northern analysis of multiple tissues using the mouse Acadl cDNA as a probe showed two bands in all tissues examined. We found a total of three distinct mRNAs for Acadl. These three mRNAs were encoded by a single gene that we mapped to mouse chromosome 1. The three transcripts differed in the 3' untranslated region due to use of alternative polyadenylation sites. Quantitative evaluation of a multitissue Northern blot showed a varied ratio of the larger transcript as compared with the smaller transcripts.

Sample matrix effects in micellar electrokinetic capillary electrophoresis

Several factors related to sample matrix which can influence peak height in micellar electrokinetic capillary chromatography were studied. The ionic strength of the sample did not affect greatly the peak height. High concentration of surfactants or organic solvents in the sample decreased the peak height. On the other hand, using a surfactant in the sample different from the one in the electrophoresis buffer or the addition of polyethylene glycol to the sample enhanced slightly the peak height. A high surfactant concentration in the buffer increased the migration time as well as the plate number and the peak height. Matrix effects are more profound with large than with small sample injections. In general, the effect of sample matrix in MECC is much less than that observed in capillary zone electrophoresis. It is recommended to prepare the standards in the same matrix as that of the sample or to add the analytes directly to the sample to avoid any bias in the results.

Xanthine analysis in biological fluids by capillary electrophoresis

Xanthine, a precursor of uric acid, is measured here in serum, urine, and cerebrospinal fluids by capillary electrophoresis (CE) after deproteinization with acetonitrile. The migration time is about 7.5 min with a minimum detection limit of 0.4 mg/l. Different purines and pyrimidines did not interfere with the determination. The method demonstrates the suitability of the CE for determination of small molecules present in a complex matrix at levels of ca. 1mg/l. It also demonstrates that acetonitrile deproteinization is a simple and effective method for preparing samples for CE, allowing a large volume to be introduced into the capillary.

Cloning and characterization of the mouse short-chain acyl-CoA dehydrogenase cDNA

Short-chain acyl-CoA dehydrogenase (SCAD) is one of five homologous dehydrogenases that catalyze the first reaction in the beta-oxidation of fatty acids. As the name implies, the substrate for this enzyme is short-chain acyl-CoA (C4-C6). We report here the coding and 3'UT sequence of the cDNA for mouse precursor SCAD. The mouse SCAD cDNA coding sequence covers 1239 bp. This represents a 24-amino-acid leader peptide and a 388-amino-acid mature peptide. Comparison of this sequence with reported rat and human SCAD cDNA sequences reveals a high degree of homology among the three species. Comparison of the amino acid sequence with that of other acyl-CoA dehydrogenases, medium-chain acyl-CoA dehydrogenase and long-chain acyl-CoA dehydrogenase, also shows a high degree of homology.

Null allele at Bcd-1 locus in BALB/cByJ mice is due to a deletion in the short-chain acyl-CoA dehydrogenase gene and results in missplicing of mRNA

BALB/cByJ mice have a deficiency of short-chain acyl-CoA dehydrogenase (SCAD), an enzyme of fatty acid beta-oxidation. This mutant mouse strain represents the only animal model for any human inborn error of fatty acid metabolism. We have investigated the molecular basis of this defect by DNA and RNA analyses, comparing these mice with the wild-type predecessor strain BALB/cBy. We found that the mutant strain has a 278-bp deletion in the 3' end of the structural gene for SCAD and reduced steady-state levels of SCAD mRNA. Two major transcripts are produced in the mutant. One contains intronic sequence due to the absence of splicing, and the second transcript results from missplicing of a normal splice donor site to a cryptic splice acceptor site in the 3' terminal exon. Both abnormal transcripts have aberrant stop codons. These results demonstrate the molecular basis of SCAD deficiency in this unique mouse model.