Elucidating the clinical spectrum and molecular basis of HYAL2 deficiency.

PURPOSE: We previously defined biallelic HYAL2 variants causing a novel disorder in 2 families, involving orofacial clefting, facial dysmorphism, congenital heart disease, and ocular abnormalities, with Hyal2 knockout mice displaying similar phenotypes. In this study, we better define the phenotype and pathologic disease mechanism. METHODS: Clinical and genomic investigations were undertaken alongside molecular studies, including immunoblotting and immunofluorescence analyses of variant/wild-type human HYAL2 expressed in mouse fibroblasts, and in silico modeling of putative pathogenic variants. RESULTS: Ten newly identified individuals with this condition were investigated, and they were associated with 9 novel pathogenic variants. Clinical studies defined genotype-phenotype correlations and confirmed a recognizable craniofacial phenotype in addition to myopia, cleft lip/palate, and congenital cardiac anomalies as the most consistent manifestations of the condition. In silico modeling of missense variants identified likely deleterious effects on protein folding. Consistent with this, functional studies indicated that these variants cause protein instability and a concomitant cell surface absence of HYAL2 protein. CONCLUSION: These studies confirm an association between HYAL2 alterations and syndromic cleft lip/palate, provide experimental evidence for the pathogenicity of missense alleles, enable further insights into the pathomolecular basis of the disease, and delineate the core and variable clinical outcomes of the condition.

Bitter taste receptor T2R14 detects quorum sensing molecules from cariogenic Streptococcus mutans and mediates innate immune responses in gingival epithelial cells.

Host-pathogen interactions play an important role in defining the outcome of a disease. Recent studies have shown that the bacterial quorum sensing molecules (QSM) can interact with host cell membrane proteins, mainly G protein-coupled receptors (GPCRs), and induce innate immune responses. However, few studies have examined QSM-GPCR interactions and their influence on oral innate immune responses. In this study, we examined the role of bitter taste receptor T2R14 in sensing competence stimulating peptides (CSPs) secreted by cariogenic bacterium Streptococcus mutans and in mediating innate immune responses in gingival epithelial cells (GECs). Transcriptomic and western blot analyses identify T2R14 to be highly expressed in GECs. Our data show that only CSP-1 from S. mutans induces robust intracellular calcium mobilization compared to CSP-2 and CSP-3. By using CRISPR-Cas9, we demonstrate that CSP-1 induced calcium signaling and secretion of cytokines CXCL-8/IL-8, TNF-α, and IL-6 is mediated through T2R14 in GECs. Interestingly, the NF-kB signaling activated by CSP-1 in GECs was independent of T2R14. CSP-1-primed GECs attracted differentiated HL-60 immune cells (dHL-60) and this effect was abolished in T2R14 knock down GECs and also in cells primed with T2R14 antagonist 6-Methoxyflavone (6-MF). Our findings identify S. mutans CSP-1 as a peptide ligand for the T2R family. Our study establishes a novel host-pathogen interaction between cariogenic S. mutans CSP-1 and T2R14 in GECs leading to an innate immune response. Collectively, these findings suggest T2Rs as potential therapeutic targets to modulate innate immune responses upon oral bacterial infections.

Generation of prolactin-inducible protein (Pip) knockout mice by CRISPR/Cas9-mediated gene engineering.

Prolactin-inducible protein (PIP) is a multifunctional glycoprotein that is highly expressed and found in the secretions of apocrine glands such as salivary, lacrimal, and sweat glands including the mammary glands. PIP has been implicated in various diseases, including breast cancer, gross cystic disease of the breast, keratoconus of the eye, and the autoimmune Sjögren's syndrome. Here we have generated a Pip knockout (KO) mouse using the Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/CRSPR-associated (Cas)9 system. The Cas9 protein and two single guide RNAs targeting specific regions for both exons 1 and 2 of the Pip gene were microinjected into mouse embryos. The deletions and insertions promoted by CRISPR/Cas9 system on the Pip gene successfully disrupted Pip protein coding, as confirmed by PCR genotyping, sequencing, and ultimately Western blot analysis. This mouse model was generated in the inbred C57Bl/6J mouse, which exhibits lower genetic variation. This novel CRISPR Pip KO mouse model will not only be useful for future studies to interrogate the multifunctional role of PIP in physiological processes but will facilitate a broader understanding of the function of PIP in vivo while providing unprecedented insight into its role in a spectrum of diseases attributed to the deregulation of the PIP gene.

SPAM1/HYAL5 double deficiency in male mice leads to severe male subfertility caused by a cumulus-oocyte complex penetration defect.

The glycosylphosphatidylinositol-anchored sperm hyaluronidases (Hyals), sperm adhesion molecule 1 (SPAM1) and HYAL5, have long been believed to assist in sperm penetration through the cumulus-oocyte complex (COC), but their role in mammalian fertilization remains unclear. Previously, we have shown that mouse sperm devoid of either Spam1 or Hyal5 are still capable of penetrating the COC and that the loss of either Spam1 or Hyal5 alone does not cause male infertility in mice. In the present study, we found that Spam1/Hyal5 double knockout (dKO) mice produced significantly fewer offspring compared with wild-type (WT) mice, and this was due to defective COC dispersal. A comparative analysis between WT and Spam1/Hyal5 dKO epididymal sperm revealed that the absence of these 2 sperm Hyals resulted in a marked accumulation of sperm on the outside of the COC. This impaired sperm activity is likely due to the deficiency in the sperm Hyals, even though other somatic Hyals are expressed normally in the dKO mice. The fertilization ability of the Spam1/Hyal5 dKO sperm was restored by adding purified human sperm Hyal to the in vitro fertilization medium. Our results suggest that Hyal deficiency in sperm may be a significant risk factor for male sterility.-Park, S., Kim, Y.-H., Jeong, P.-S., Park, C., Lee, J.-W., Kim, J.-S., Wee, G., Song, B.-S., Park, B.-J., Kim, S.-H., Sim, B.-W., Kim, S.-U., Triggs-Raine, B., Baba, T., Lee, S.-R., Kim, E. SPAM1/HYAL5 double deficiency in male mice leads to severe male subfertility caused by a cumulus-oocyte complex penetration defect.

Mutations in HYAL2, Encoding Hyaluronidase 2, Cause a Syndrome of Orofacial Clefting and Cor Triatriatum Sinister in Humans and Mice.

Orofacial clefting is amongst the most common of birth defects, with both genetic and environmental components. Although numerous studies have been undertaken to investigate the complexities of the genetic etiology of this heterogeneous condition, this factor remains incompletely understood. Here, we describe mutations in the HYAL2 gene as a cause of syndromic orofacial clefting. HYAL2, encoding hyaluronidase 2, degrades extracellular hyaluronan, a critical component of the developing heart and palatal shelf matrix. Transfection assays demonstrated that the gene mutations destabilize the molecule, dramatically reducing HYAL2 protein levels. Consistent with the clinical presentation in affected individuals, investigations of Hyal2-/- mice revealed craniofacial abnormalities, including submucosal cleft palate. In addition, cor triatriatum sinister and hearing loss, identified in a proportion of Hyal2-/- mice, were also found as incompletely penetrant features in affected humans. Taken together our findings identify a new genetic cause of orofacial clefting in humans and mice, and define the first molecular cause of human cor triatriatum sinister, illustrating the fundamental importance of HYAL2 and hyaluronan turnover for normal human and mouse development.

Increase of a group of PTC(+) transcripts by curcumin through inhibition of the NMD pathway.

Nonsense-mediated mRNA decay (NMD), an mRNA surveillance mechanism, eliminates premature termination codon-containing (PTC⁺) transcripts. For instance, it maintains the homeostasis of splicing factors and degrades aberrant transcripts of human genetic disease genes. Here we examine the inhibitory effect on the NMD pathway and consequent increase of PTC+ transcripts by the dietary compound curcumin. We have found that several PTC⁺ transcripts including that of serine/arginine-rich splicing factor 1 (SRSF1) were specifically increased in cells by curcumin. We also observed a similar curcumin effect on the PTC⁺ mutant transcript from a Tay-Sachs-causing HEXA allele or from a beta-globin reporter gene. The curcumin effect was accompanied by significantly reduced expression of the NMD factors UPF1, 2, 3A and 3B. Consistently, in chromatin immunoprecipitation assays, curcumin specifically reduced the occupancy of acetyl-histone H3 and RNA polymerase II at the promoter region (-376 to -247nt) of human UPF1, in a time- and dosage-dependent way. Importantly, knocking down UPF1 abolished or substantially reduced the difference of PTC(+) transcript levels between control and curcumin-treated cells. The disrupted curcumin effect was efficiently rescued by expression of exogenous Myc-UPF1 in the knockdown cells. Together, our data demonstrate that a group of PTC⁺ transcripts are stabilized by a dietary compound curcumin through the inhibition of UPF factor expression and the NMD pathway.

Growth arrest in the ribosomopathy, Bowen-Conradi syndrome, is due to dramatically reduced cell proliferation and a defect in mitotic progression.

Bowen-Conradi syndrome (BCS) is a ribosomopathy characterized by severe developmental delay and growth failure that typically leads to death by one year of age. It is caused by a c.257A>G, p.D86G substitution in the ribosomal biogenesis protein, Essential for Mitotic Growth 1 (EMG1). We generated a knock-in of the D86G substitution in mice to characterize the effects of EMG1 deficiency, particularly in the brain, where EMG1 expression is high. Embryos homozygous for the mutation in Emg1 were small for gestational age with neural tube defects, and died between embryonic days 8.5 and 12.5. These embryos exhibited dramatically reduced cell proliferation, which we also detected in autopsy brain tissue and bone marrow of BCS patients, consistent with a requirement for high levels of EMG1 in tissues with rapid cell proliferation. In fibroblasts derived from the BCS mouse embryos, we detected a high proportion of binucleated cells, indicating that a mitotic defect underlies the growth arrest in BCS. These studies add to growing evidence of a link between ribosome biogenesis, mitotic progression, and brain development that is currently unexplored.

Hyaluronidase 2 (HYAL2) is expressed in endothelial cells, as well as some specialized epithelial cells, and is required for normal hyaluronan catabolism.

Hyaluronidase 2 (HYAL2) is a membrane-anchored protein that is proposed to initiate the degradation of hyaluronan (HA) in the extracellular matrix. The distribution of HYAL2 in tissues, and of HA in tissues lacking HYAL2, is largely unexplored despite the importance of HA metabolism in several disease processes. Herein, we use immunoblot and histochemical analyses to detect HYAL2 and HA in mouse tissues, as well as agarose gel electrophoresis to examine the size of HA. HYAL2 was detected in all tissues that were examined, including the brain. It was localized to the surface and cytoplasm of endothelial cells, as well as specialized epithelial cells in several tissues, including the skin. Accumulated HA, often of higher molecular mass than that in control tissues, was detected in tissues from Hyal2 (-/-) mice. The accumulating HA was located near to where HYAL2 is normally found, although in some tissues, it was distant from the site of HYAL2 localization. Overall, HYAL2 was highest in tissues that remove HA from the circulation (liver, lymph node and spleen), but the levels of HA accumulation in Hyal2 (-/-) mice were highest in tissues that catabolize locally synthesized HA. Our results support HYAL2's role as an extracellular enzyme that initiates HA breakdown in somatic tissues. However, our findings also suggest that HYAL2 contributes to HA degradation through other routes, perhaps as a soluble or secreted form.

Long-term correction of Sandhoff disease following intravenous delivery of rAAV9 to mouse neonates.

G(M2) gangliosidoses are severe neurodegenerative disorders resulting from a deficiency in ß-hexosaminidase A activity and lacking effective therapies. Using a Sandhoff disease (SD) mouse model (Hexb(-/-)) of the G(M2) gangliosidoses, we tested the potential of systemically delivered adeno-associated virus 9 (AAV9) expressing Hexb cDNA to correct the neurological phenotype. Neonatal or adult SD and normal mice were intravenously injected with AAV9-HexB or -LacZ and monitored for serum ß-hexosaminidase activity, motor function, and survival. Brain G(M2) ganglioside, ß-hexosaminidase activity, and inflammation were assessed at experimental week 43, or an earlier humane end point. SD mice injected with AAV9-LacZ died by 17 weeks of age, whereas all neonatal AAV9-HexB-treated SD mice survived until 43 weeks (P < 0.0001) with only three exhibiting neurological dysfunction. SD mice treated as adults with AAV9-HexB died between 17 and 35 weeks. Neonatal SD-HexB-treated mice had a significant increase in brain ß-hexosaminidase activity, and a reduction in G(M2) ganglioside storage and neuroinflammation compared to adult SD-HexB- and SD-LacZ-treated groups. However, at 43 weeks, 8 of 10 neonatal-HexB injected control and SD mice exhibited liver or lung tumors. This study demonstrates the potential for long-term correction of SD and other G(M2) gangliosidoses through early rAAV9 based systemic gene therapy.

GPSM2 mutations cause the brain malformations and hearing loss in Chudley-McCullough syndrome.

Autosomal-recessive inheritance, severe to profound sensorineural hearing loss, and partial agenesis of the corpus callosum are hallmarks of the clinically well-established Chudley-McCullough syndrome (CMS). Although not always reported in the literature, frontal polymicrogyria and gray matter heterotopia are uniformly present, whereas cerebellar dysplasia, ventriculomegaly, and arachnoid cysts are nearly invariant. Despite these striking brain malformations, individuals with CMS generally do not present with significant neurodevelopmental abnormalities, except for hearing loss. Homozygosity mapping and whole-exome sequencing of DNA from affected individuals in eight families (including the family in the first report of CMS) revealed four molecular variations (two single-base deletions, a nonsense mutation, and a canonical splice-site mutation) in the G protein-signaling modulator 2 gene, GPSM2, that underlie CMS. Mutations in GPSM2 have been previously identified in people with profound congenital nonsyndromic hearing loss (NSHL). Subsequent brain imaging of these individuals revealed frontal polymicrogyria, abnormal corpus callosum, and gray matter heterotopia, consistent with a CMS diagnosis, but no ventriculomegaly. The gene product, GPSM2, is required for orienting the mitotic spindle during cell division in multiple tissues, suggesting that the sensorineural hearing loss and characteristic brain malformations of CMS are due to defects in asymmetric cell divisions during development.

Murine hyaluronidase 2 deficiency results in extracellular hyaluronan accumulation and severe cardiopulmonary dysfunction.

Hyaluronidase (HYAL) 2 is a membrane-anchored protein that is proposed to hydrolyze hyaluronan (HA) to smaller fragments that are internalized for breakdown. Initial studies of a Hyal2 knock-out (KO) mouse revealed a mild phenotype with high serum HA, supporting a role for HYAL2 in HA breakdown. We now describe a severe cardiac phenotype, deemed acute, in 54% of Hyal2 KO mice on an outbred background; Hyal2 KO mice without the severe cardiac phenotype were designated non-acute. Histological studies of the heart revealed that the valves of all Hyal2 KO mice were expanded and the extracellular matrix was disorganized. HA was detected throughout the expanded valves, and electron microscopy confirmed that the accumulating material, presumed to be HA, was extracellular. Both acute and non-acute Hyal2 KO mice also exhibited increased HA in the interstitial extracellular matrix of atrial cardiomyocytes compared with control mice. Consistent with the changes in heart structure, upper ventricular cardiomyocytes in acute Hyal2 KO mice demonstrated significant hypertrophy compared with non-acute KO and control mice. When the lungs were examined, evidence of severe fibrosis was detected in acute Hyal2 KO mice but not in non-acute Hyal2 KO or control mice. Total serum and heart HA levels, as well as size, were increased in acute and non-acute Hyal2 KO mice compared with control mice. These findings indicate that HYAL2 is essential for the breakdown of extracellular HA. In its absence, extracellular HA accumulates and, in some cases, can lead to cardiopulmonary dysfunction. Alterations in HYAL2 function should be considered as a potential contributor to cardiac pathologies in humans.

Characterization of HMGA2 variants expands the spectrum of Silver-Russell syndrome.

Silver-Russell syndrome (SRS) is a heterogeneous disorder characterized by intrauterine and postnatal growth retardation. HMGA2 variants are a rare cause of SRS and its functional role in human linear growth is unclear. Patients with suspected SRS negative for 11p15LOM/mUPD7 underwent whole-exome and/or targeted-genome sequencing. Mutant HMGA2 protein expression and nuclear localization were assessed. Two Hmga2-knockin mouse models were generated. Five clinical SRS patients harbored HMGA2 variants with differing functional impacts: 2 stop-gain nonsense variants (c.49G>T, c.52C>T), c.166A>G missense variant, and 2 frameshift variants (c.144delC, c.145delA) leading to an identical, extended-length protein. Phenotypic features were highly variable. Nuclear localization was reduced/absent for all variants except c.166A>G. Homozygous knockin mice recapitulating the c.166A>G variant (Hmga2K56E) exhibited a growth-restricted phenotype. An Hmga2Ter76-knockin mouse model lacked detectable full-length Hmga2 protein, similarly to patient 3 and 5 variants. These mice were infertile, with a pygmy phenotype. We report a heterogeneous group of individuals with SRS harboring variants in HMGA2 and describe the first Hmga2 missense knockin mouse model (Hmga2K56E) to our knowledge causing a growth-restricted phenotype. In patients with clinical features of SRS but negative genetic screening, HMGA2 should be included in next-generation sequencing testing approaches.

Hyaluronidase 1 and ß-hexosaminidase have redundant functions in hyaluronan and chondroitin sulfate degradation.

Hyaluronan (HA), a member of the glycosaminoglycan (GAG) family, is a critical component of the extracellular matrix. A model for HA degradation that invokes the activity of both hyaluronidases and exoglycosidases has been advanced. However, no in vivo studies have been done to determine the extent to which these enzymes contribute to HA breakdown. Herein, we used mouse models to investigate the contributions of the endoglycosidase HYAL1 and the exoglycosidase ß-hexosaminidase to the lysosomal degradation of HA. We employed histochemistry and fluorophore-assisted carbohydrate electrophoresis to determine the degree of HA accumulation in mice deficient in one or both enzyme activities. Global HA accumulation was present in mice deficient in both enzymes, with the highest levels found in the lymph node and liver. Chondroitin, a GAG similar in structure to HA, also broadly accumulated in mice deficient in both enzymes. Accumulation of chondroitin sulfate derivatives was detected in mice deficient in both enzymes, as well as in ß-hexosaminidase-deficient mice, indicating that both enzymes play a significant role in chondroitin sulfate breakdown. Extensive accumulation of HA and chondroitin when both enzymes are lacking was not observed in mice deficient in only one of these enzymes, suggesting that HYAL1 and ß-hexosaminidase are functionally redundant in HA and chondroitin breakdown. Furthermore, accumulation of sulfated chondroitin in tissues provides in vivo evidence that both HYAL1 and ß-hexosaminidase cleave chondroitin sulfate, but it is a preferred substrate for ß-hexosaminidase. These studies provide in vivo evidence to support and extend existing knowledge of GAG breakdown.

Hyal-1 but not Hyal-3 deficiency has an impact on ovarian folliculogenesis and female fertility by altering the follistatin/activin/Smad3 pathway and the apoptotic process.

Ovarian follicle development is a process regulated by various endocrine, paracrine and autocrine factors that act coordinately to promote follicle growth. However, the vast majority of follicles does not reach the pre-ovulatory stage but instead, undergo atresia by apoptosis. We have recently described a role for the somatic hyaluronidases (Hyal-1, Hyal-2, and Hyal-3) in ovarian follicular atresia and induction of granulosa cell apoptosis. Herein, we show that Hyal-1 but not Hyal-3 null mice have decreased apoptotic granulosa cells after the induction of atresia and an increased number of retrieved oocytes after stimulation of ovulation. Furthermore, young Hyal-1 null mice had a significantly higher number of primordial follicles than age matched wild-type animals. Recruitment of these follicles at puberty resulted in an increased number of primary and healthy preantral follicles in Hyal-1 null mice. Consequently, older Hyal-1 deficient female mice have prolonged fertility. At the molecular level, immature Hyal-1 null mice have decreased mRNA expression of follistatin and higher levels of phospho-Smad3 protein, resulting in increased levels of phospho-Akt in pubertal mice. Hyal-1 null ovarian follicles did not exhibit hyaluronan accumulation. For Hyal-3 null mice, compensation by Hyal-1 or Hyal-2 might be related to the lack of an ovarian phenotype. In conclusion, our results demonstrate that Hyal-1 plays a key role in the early phases of folliculogenesis by negatively regulating ovarian follicle growth and survival. Our findings add Hyal-1 as an ovarian regulator factor for follicle development, showing for the first time an interrelationship between this enzyme and the follistatin/activin/Smad3 pathway.

Mutation of a gene essential for ribosome biogenesis, EMG1, causes Bowen-Conradi syndrome.

Bowen-Conradi syndrome (BCS) is an autosomal-recessive disorder characterized by severely impaired prenatal and postnatal growth, profound psychomotor retardation, and death in early childhood. Nearly all reported BCS cases have been among Hutterites, with an estimated birth prevalence of 1/355. We previously localized the BCS gene to a 1.9 Mbp interval on human chromosome 12p13.3. The 59 genes in this interval were ranked as candidates for BCS, and 35 of these, including all of the best candidates, were sequenced. We identified variant NM_006331.6:c.400A-->G, p.D86G in the 18S ribosome assembly protein EMG1 as the probable cause of BCS. This mutation segregated with disease, was not found in 414 non-Hutterite alleles, and altered a highly conserved aspartic acid (D) residue. A structural model of human EMG1 suggested that the D86 residue formed a salt bridge with arginine 84 that would be disrupted by the glycine (G) substitution. EMG1 mRNA was detected in all human adult and fetal tissues tested. In BCS patient fibroblasts, EMG1 mRNA levels did not differ from those of normal cells, but EMG1 protein was dramatically reduced in comparison to that of normal controls. In mammalian cells, overexpression of EMG1 harboring the D86G mutation decreased the level of soluble EMG1 protein, and in yeast two-hybrid analysis, the D86G substitution increased interaction between EMG1 subunits. These findings suggested that the D-to-G mutation caused aggregation of EMG1, thereby reducing the level of the protein and causing BCS.

The adult polyglucosan body disease mutation GBE1 c.1076A>C occurs at high frequency in persons of Ashkenazi Jewish background.

Mutations of the glycogen branching enzyme gene, GBE1, result in glycogen storage disease (GSD) type IV, an autosomal recessive disorder having multiple clinical forms. One mutant allele of this gene, GBE1 c.1076A>C, has been reported in Ashkenazi Jewish cases of an adult-onset form of GSD type IV, adult polyglucosan body disease (APBD), but no epidemiological analyses of this mutation have been performed. We report here the first epidemiological study of this mutation in persons of Ashkenazi Jewish background and find that this mutation has a gene frequency of 1 in 34.5 (95% CI: 0.0145-0.0512), similar to the frequency of the common mutation causing Tay-Sachs disease among Ashkenazi Jews. This finding reveals APBD to be another monogenic disorder that occurs with increased frequency in persons of Ashkenazi Jewish ancestry.

Increased phosphorylation of HexM improves lysosomal uptake and potential for managing GM2 gangliosidoses.

Tay-Sachs and Sandhoff diseases are genetic disorders resulting from mutations in HEXA or HEXB, which code for the α- and ß-subunits of the heterodimer ß-hexosaminidase A (HexA), respectively. Loss of HexA activity results in the accumulation of GM2 ganglioside (GM2) in neuronal lysosomes, culminating in neurodegeneration and death, often by age 4. Previously, we combined critical features of the α- and ß-subunits of HexA into a single subunit to create a homodimeric enzyme known as HexM. HexM is twice as active as HexA and degrades GM2 in vivo, making it a candidate for enzyme replacement therapy (ERT). Here we show HexM production is scalable to meet ERT requirements and we describe an approach that enhances its cellular uptake via co-expression with an engineered GlcNAc-1-phosphotransferase that highly phosphorylates lysosomal proteins. Further, we developed a HexA overexpression system and functionally compared the recombinant enzyme to HexM, revealing the kinetic differences between the enzymes. This study further advances HexM as an ERT candidate and provides a convenient system to produce HexA for comparative studies.

A complete deficiency of Hyaluronoglucosaminidase 1 (HYAL1) presenting as familial juvenile idiopathic arthritis.

We describe a single consanguineous family with three affected children exhibiting knee and/or hip pain associated with swelling. Detailed clinical evaluation demonstrated diffuse joint involvement with an unusual proliferative synovitis on MRI. Synovial biopsies were notable for an infiltration of macrophages with abundant cytoplasm filled with faintly basophilic vacuoles. We used homozygosity mapping with a panel of 262,000 single nucleotide polymorphism markers to identify a homozygous stretch of 40.52 Mb on chromosome 3p22.3 - 3p13 that segregated with the arthropathy in the family. Of the 378 genes in the interval, the three hyaluronoglucosaminidase genes were considered good candidates based on the phenotype. Dideoxy sequencing identified a homozygous deletion in HYAL1, c.104delT, resulting in a premature termination codon, p.Val35AlafsX25, found in all three affected children. Enzymatic analysis confirmed total HYAL1 deficiency in the three affected children. This confirms the diagnosis of Mucopolysaccharidosis IX (MPS IX) which has only been described in a single patient to date. In contrast to the previously described MPS IX patient, our three patients display a phenotype limited to the joints, suggesting that this is the primary manifestation of HYAL1 deficiency.

EMG1 is essential for mouse pre-implantation embryo development.

BACKGROUND: Essential for mitotic growth 1 (EMG1) is a highly conserved nucleolar protein identified in yeast to have a critical function in ribosome biogenesis. A mutation in the human EMG1 homolog causes Bowen-Conradi syndrome (BCS), a developmental disorder characterized by severe growth failure and psychomotor retardation leading to death in early childhood. To begin to understand the role of EMG1 in mammalian development, and how its deficiency could lead to Bowen-Conradi syndrome, we have used mouse as a model. The expression of Emg1 during mouse development was examined and mice carrying a null mutation for Emg1 were generated and characterized. RESULTS: Our studies indicated that Emg1 is broadly expressed during early mouse embryonic development. However, in late embryonic stages and during postnatal development, Emg1 exhibited specific expression patterns. To assess a developmental role for EMG1 in vivo, we exploited a mouse gene-targeting approach. Loss of EMG1 function in mice arrested embryonic development prior to the blastocyst stage. The arrested Emg1-/- embryos exhibited defects in early cell lineage-specification as well as in nucleologenesis. Further, loss of p53, which has been shown to rescue some phenotypes resulting from defects in ribosome biogenesis, failed to rescue the Emg1-/- pre-implantation lethality. CONCLUSION: Our data demonstrate that Emg1 is highly expressed during mouse embryonic development, and essential for mouse pre-implantation development. The absolute requirement for EMG1 in early embryonic development is consistent with its essential role in yeast. Further, our findings also lend support to the previous study that showed Bowen-Conradi syndrome results from a partial EMG1 deficiency. A complete deficiency would not be expected to be compatible with a live birth.

A mouse model of human mucopolysaccharidosis IX exhibits osteoarthritis.

Hyaluronidases are endoglycosidases that hydrolyze hyaluronan (HA), an abundant component of the extracellular matrix of vertebrate connective tissues. Six human hyaluronidase-related genes have been identified to date. Mutations in one of these genes cause a deficiency of hyaluronidase 1 (HYAL1) resulting in a lysosomal storage disorder, mucopolysaccharidosis (MPS) IX. We have characterized a mouse model of MPS IX and compared its phenotype with the human disease. The targeted Hyal1 allele in this model had a neomycin resistance cassette in exon 2 that replaced 753 bp of the coding region containing the predicted enzyme active site. As a result, Hyal1(-/-) animals had no detectable wild-type Hyal1 transcript, protein or serum activity. Hyal1 null animals were viable, fertile and showed no gross abnormalities at 1 year and 8 months of age. Histological studies of the knee joint showed a loss of proteoglycans occurring as early as 3 months that progressed with age. An increased number of chondrocytes displaying intense pericellular and/or cytoplasmic HA staining were detected in the epiphyseal and articular cartilage of null mice, demonstrating an accumulation of HA. Elevations of HA were not detected in the serum or non-skeletal tissues, indicating that osteoarthritis is the key disease feature in a Hyal1 deficiency. Hyal3 expression was elevated in Hyal1 null mice, suggesting that Hyal3 may compensate in HA degradation in non-skeletal tissues. Overall, the murine MPS IX model displays the key features of the human disease.