Mice deficient in the axonemal protein Tektin-t exhibit male infertility and immotile-cilium syndrome due to impaired inner arm dynein function

The haploid germ cell-specific Tektin-t protein is a member of the Tektin family of proteins that form filaments in flagellar, ciliary, and axonemal microtubules. To investigate the physiological role of Tektin-t, we generated mice with a mutation in the tektin-t gene. The homozygous mutant males were infertile, while the females were fully fertile. Sperm morphology and function were abnormal, with frequent bending of the sperm flagella and marked defects in motility. In vitro fertilization assays showed that the defective spermatozoa were able to fertilize eggs. Electron microscopic examination showed that the dynein inner arm structure was disrupted in the sperm flagella of tektin-t-deficient mice. Furthermore, homozygous mutant mice had functionally defective tracheal cilia, as evidenced by altered dynein arm morphology. These results indicate that Tektin-t participates in dynein inner arm formation or attachment and that the loss of Tektin-t results in impaired motility of both flagella and cilia. Therefore, the tektin-t gene is one of the causal genes for immotile-cilium syndrome/primary ciliary dyskinesia.     

A mutation in the Lunatic fringe gene suppresses the effects of a Jagged2 mutation on inner hair cell development in the cochlea

Recent studies have demonstrated that the Notch signaling pathway regulates the differentiation of sensory hair cells in the vertebrate inner ear [1] [2] [3] [4] [5] [6] [7] [8] [9]. We have shown previously that in mice homozygous for a targeted null mutation of the Jagged2 (Jag2) gene, which encodes a Notch ligand, supernumerary hair cells differentiate in the cochlea of the inner ear [7]. Other components of the Notch pathway, including the Lunatic fringe (Lfng) gene, are also expressed during differentiation of the inner ear in mice [6] [7] [8] [9] [10]. In contrast to the Jag2 gene, which is expressed in hair cells, the Lfng gene is expressed in non-sensory supporting cells in the mouse cochlea [10]. Here we demonstrate that a mutation in the Lfng gene partially suppresses the effects of the Jag2 mutation on hair cell development. In mice homozygous for targeted mutations of both Jag2 and Lfng, the generation of supernumerary hair cells in the inner hair cell row is suppressed, while supernumerary hair cells in the outer hair cell rows are unaffected. We also demonstrate that supernumerary hair cells are generated in mice heterozygous for a Notch1 mutation. We suggest a model for the action of the Notch signaling pathway in regulating hair cell differentiation in the cochlear sensory epithelium.     

The mutant gene wellhaarig disturbs the differentiation of hair follicle cells in the mouse]

First generation (G1) hairs in mice homozygous for the wellhaarig (we) gene are wavy and shorter than in normal mice; basal regions of the hairs are deformed. Follicles of G1 hairs in mid-dorsal region of 8-, 12- and 16-days old we/we mice were examined. Huxley cells of the inner root sheath (IRS) in apical region of hair follicles appeared to be hypertrophied. Cytoplasm of these cells was not stained by basic dyes and showed no birefringence. Cytoplasm of the IRS Henle cells was not stained by basic dyes either. These data indicate that keratinization of the IRS cells is disturbed in mutant homozygotes. The layer of outer root sheath in the we/we mice was thinner than in normal mice; this is probably due to hypertrophy of the IRS cells. The structure of differentiating cells of the hair shaft in normal and mutant mice was similar. The data obtained suggest that abnormal G1 hairs in we/we mice result from disturbance in IRS cells differentiation.     

The mouse mutation claw paw: forelimb deformity and delayed myelination throughout the peripheral nervous system.

We describe a murine autosomal recessive mutation claw paw (gene symbol clp), which in homozygous clp/clp mice produces striking abnormalities of limb posture within the first one or two postnatal days. Affected animals have delayed and abnormal myelination in the peripheral nervous system but not in the central nervous system, and also have persistently blocked myelination of small caliber axons that are myelinated in normal mice. Both abnormalities suggest that an important effect of the clp mutation is to impair the putative signaling mechanism by which an axon instructs a Schwann cell whether or not to myelinate it. The early onset of behavioral abnormalities in clp/clp mutant mice, as well as certain other features of the disorder, suggest that some effects of the clp gene are not accounted for by the pathological findings. The clp gene has been mapped to chromosome 7 near the Gpi-1 locus.     

Molecular mechanisms underlying inner ear patterning defects in kreisler mutants

Prior studies have shown that kreisler mutants display early inner ear defects that are related to abnormal hindbrain development and signaling. These defects in kreisler mice have been linked to mutation of the kr/mafB gene. To investigate potential relevance of kr/mafB and abnormal hindbrain development in inner ear patterning, we analyzed the ear morphogenesis in kreisler mice using a paint-fill technique. We also examined the expression patterns of a battery of genes important for normal inner ear patterning and development. Our results indicate that the loss of dorsal otic structures such as the endolymphatic duct and sac is attributable to the downregulation of Gbx2, Dlx5 and Wnt2b in the dorsal region of the otocyst. In contrast, the expanded expression domain of Otx2 in the ventral otic region likely contributes to the cochlear phenotype seen in kreisler mutants. Sensory organ development is also markedly disrupted in kreisler mutants. This pattern of defects and gene expression changes is remarkably similar to that observed in Gbx2 mutants. Taken together, the data show an important role for hindbrain cues, and indirectly, kr/mafB, in guiding inner ear morphogenesis. The data also identify Gbx2, Dlx5, Wnt2b and Otx2 as key otic genes ultimately affected by perturbation of the kr/mafB-hindbrain pathway.     

Altered gene expression in liver from a murine model of hyperhomocysteinemia

Cystathionine beta-synthase (CBS) deficiency causes severe hyperhomocysteinemia and other signs of homocystinuria syndrome, in particular a premature atherosclerosis with multiple thrombosis. However, the molecular mechanisms by which homocysteine could interfere with normal cell function are poorly understood in a whole organ like the liver, which is central to the catabolism of homocysteine. We used a combination of differential display and cDNA arrays to analyze differential gene expression in association with elevated hepatic homocysteine levels in CBS-deficient mice, a murine model of hyperhomocysteinemia. Expression of several genes was found to be reproducibly abnormal in the livers of heterozygous and homozygous CBS-deficient mice. We report altered expression of genes encoding ribosomal protein S3a and methylthioadenosine phosphorylase, suggesting such cellular growth and proliferation perturbations may occur in homozygous CBS-deficient mice liver. Many up- or down-regulated genes encoded cytochromes P450, evidence of perturbations of the redox potential in heterozygous and homozygous CBS-deficient mice liver. The expression of various genes involved in severe oxidative processes was also abnormal in homozygous CBS-deficient mice liver. Among them, the expression of heme oxygenase 1 gene was increased, concomitant with overexpression of heme oxygenase 1 at the protein level. Commensurate with the difference in hepatic mRNA paraoxonase 1 abundance, the mean hepatic activity of paraoxonase 1, an enzyme that protects low density lipoprotein from oxidation, was 3-fold lower in homozygous CBS-deficient mice. Heterozygous CBS-deficient mice, when fed a hyperhomocysteinemic diet, have also reduced PON1 activity, which demonstrates the effect of hyperhomocysteinemia in the paraoxonase 1 activity.     

PMCA2 mutation causes structural changes in the auditory system in deafwaddler mice

Homozygous deafwaddler mice (dfw/dfw) have a mutation in the gene encoding plasma membrane Ca²⁺ATPase isoform 2 (Pmca2). They walk with a hesitant and wobbly gait, display head bobbing and are deaf. Light microscopy and transmission electron microscopy were used to evaluate the nature and relationship of morphological changes in the cochlea, spiral ganglion cells and spherical cells of the cochlear nucleus in homozygous and heterozygous mice of different ages and controls. Ultrastructural findings showed that in 7 week old homozygous (dfw) mice, inner hair cells and their afferent terminals were present although outer hair cells appeared apoptotic. Stereocilia were absent from the second and third rows of outer hair cells. Ganglion cells were also present although abnormal in appearance. In older homozygous mutants there was a loss of hair cells and spiral ganglion cells. Remaining ganglion cells in this group contained very few cytoplasmic organelles apart from a few hypertrophied mitochondria. In the anteroventral cochlear nucleus, spherical cell soma size was smaller in all homozygous (dfw) mutants than in heterozygous mice and controls. The ultrastructural appearance of the end bulbs of Held in homozygous mutants was abnormal compared with controls, and in the younger group were seen to be swollen, with less distinct synaptic densities and containing large numbers of small synaptic vesicles arranged in clumps. In the older group these synapses were distorted and contained hypertrophied mitochondria and no synaptic densities could be seen, suggesting that these synapses may be non-functional. This study has shown that in homozygous (dfw) mice structural abnormalities occurred not only in cochlear hair cells but also in the spiral ganglion neurones and spherical cells in the cochlear nucleus. It seems likely that these changes are the result of the Pmca2 mutation and the subsequent accumulation of toxic levels of calcium that may lead to alterations in their functional integrity.     

Aberrant axonal projections in mice lacking EphA8 (Eek) tyrosine protein kinase receptors.

We have generated mice homozygous for a mutation that disrupts the gene encoding EphA8, a member of the Eph family of tyrosine protein kinase receptors, previously known as Eek. These mice develop to term, are fertile and do not display obvious anatomical or physiological defects. The mouse ephA8/eek gene is expressed primarily in a rostral to caudal gradient in the developing tectum. Axonal tracing experiments have revealed that in these mutant mice, axons from a subpopulation of tectal neurons located in the superficial layers of the superior colliculus do not reach targets located in the contralateral inferior colliculus. Moreover, ephA8/eek null animals display an aberrant ipsilateral axonal tract that projects to the ventral region of the cervical spinal cord. Retrograde labeling revealed that these abnormal projections originate from a small subpopulation of superior colliculus neurons that normally express the ephA8/eek gene. These results suggest that EphA8/Eek receptors play a role in axonal pathfinding during development of the mammalian nervous system.     

The T3R alpha gene encoding a thyroid hormone receptor is essential for post-natal development and thyroid hormone production.

The diverse functions of thyroid hormones are thought to be mediated by two nuclear receptors, T3R alpha1 and T3R beta, encoded by the genes T3R alpha and T3R beta respectively. The T3R alpha gene also produces a non-ligand-binding protein T3R alpha2. The in vivo functions of these receptors are still unclear. We describe here the homozygous inactivation of the T3R alpha gene which abrogates the production of both T3R alpha1 and T3R alpha2 isoforms and that leads to death in mice within 5 weeks after birth. After 2 weeks of life, the homozygous mice become progressively hypothyroidic and exhibit a growth arrest. Small intestine and bones showed a strongly delayed maturation. In contrast to the negative regulatory function of the T3R beta gene on thyroid hormone production, our data show that the T3R alpha gene products are involved in up-regulation of thyroid hormone production at weaning time. Thus, thyroid hormone production might be balanced through a positive T3R alpha and a negative T3R beta pathway. The abnormal phenotypes observed on the homozygous mutant mice strongly suggest that the T3R alpha gene is essential for the transformation of a mother-dependent pup to an 'adult' mouse. These data define crucial in vivo functions for thyroid hormones through a T3R alpha pathway during post-natal development.     

Ectopic expression of tmie transgene induces various recovery levels of behavior and hearing ability in the circling mouse

The circling (cir/cir) mouse is one of the murine models for human non-syndromic deafness DFNB6. The mice have abnormal circling behavior, suggesting a balanced disorder and profound deafness. The causative gene was transmembrane inner ear (tmie) gene of which the mutation is a 40-kb genomic deletion including tmie gene itself. In this study, tmie-overexpression trasngenic mice were established. Individuals with germline transmission have been mated with circling homozygous mutant mice (cir/cir) in order to produce the transgenic mutant mice (cir/cir-tg) as a gene therapy. After the genotyping, phenotypic analyses were performed so that the insertion of the new gene might compensate for the diseases such as hearing loss, circling behavior, or swimming inability. Some individuals exhibited complete recovery in their behavior and hearing but the others did not show any amelioration in behavior or hearing. Individual mice had very different levels of tmie transgene expression in the cochlea. These results clearly indicate that tmie protein plays an important role when the appropriate expression level of tmie was expressed in the inner ear. The protein levels were variable in each individual and these are thought to induce the differences in disease amelioration levels.     

A transgene carrying an A2G missense mutation in the SMN gene modulates phenotypic severity in mice with severe (type I) spinal muscular atrophy

5q spinal muscular atrophy (SMA) is a common autosomal recessive disorder in humans and the leading genetic cause of infantile death. Patients lack a functional survival of motor neurons (SMN1) gene, but carry one or more copies of the highly homologous SMN2 gene. A homozygous knockout of the single murine Smn gene is embryonic lethal. Here we report that in the absence of the SMN2 gene, a mutant SMN A2G transgene is unable to rescue the embryonic lethality. In its presence, the A2G transgene delays the onset of motor neuron loss, resulting in mice with mild SMA. We suggest that only in the presence of low levels of full-length SMN is the A2G transgene able to form partially functional higher order SMN complexes essential for its functions. Mild SMA mice exhibit motor neuron degeneration, muscle atrophy, and abnormal EMGs. Animals homozygous for the mutant transgene are less severely affected than heterozygotes. This demonstrates the importance of SMN levels in SMA even if the protein is expressed from a mutant allele. Our mild SMA mice will be useful in (a) determining the effect of missense mutations in vivo and in motor neurons and (b) testing potential therapies in SMA.     

Myelin deficient mice: expression of myelin basic protein and generation of mice with varying levels of myelin

Mice homozygous for the mutation myelin deficient (mld), an allele of shiverer, exhibit decreased CNS myelination, tremors, and convulsions of progressively increasing severity leading to an early death. In this report we demonstrate in mld mice that the gene encoding myelin basic protein (MBP) is expressed at decreased levels and on an abnormal temporal schedule relative to the wild-type gene. Southern blot analyses, field-inversion gel electrophoresis studies, and analyses of mld MBP cosmid clones indicate that there are multiple linked copies of the MBP gene in mld mice. We have introduced an MBP transgene into mld mice and found that myelination increases and tremors and convulsions decrease. Mld and shiverer mice with zero, one, or two copies of the MBP transgene express distinct levels of MBP mRNA and myelin. The availability of a range of mice expressing graded levels of myelin should facilitate quantitative analysis of the roles of MBP in the myelination process and of myelin in nerve function.     

Abnormal bone production associated with mutant mouse genes pa and we

A syndrome including deficient linear, endochondral, and radial bone growth associated with severe cervico-thoracic lordosis, decreased intrathoracic volume, atelectasis, and early death has been noted in mice possessing the phenotypes of the recessive mutant genes pallid (pa) and wellhaarig (we) as the result of recombination of chromosome 2 between these genes. The syndrome is not seen in the parental strains, which are homozygous for the chromosomal segment containing one or the other gene (pa +/pa + or + we/+ we), nor in the intercross mice heterozygous for both genes in the trans configuration (pa+/+we). The abnormal offspring appeared randomly in the breeding colony with no F1 breeding pair producing more than one pa we mouse. These observations rule out the presence of a mutant gene, fixed or unfixed, as an explanation for this syndrome. We hypothesize that the syndrome is the result of the complementary action of the genes or the chromosomal segments containing the genes pa and we or weBkr. The posited synergism is further supported by the finding that we, which functions as a recessive gene in mice of the pa/+ genotype, appears to function as a dominant gene in mice possessing the pa/pa genotype.     

Gene angora as a modifier of the mouse hairless gene

The interactions between mouse angora-Y (Fgf5go-Y) and hairless (hr) genes have been studied. Homozygous mutant gene Fgf5go-Y increases hair length starting on day 14 after birth. We obtained mice with genotypes +/+ hr/hr F2, +/Fgf5go-Y hr/hr and Fgf5go-Y/Fgf5go-Y hr/hr. Both +/Fgf5go-Y hr/hr and +/+ hr/hr mice began to loose hair from their heads on day 14. This further extended on the whole body. On day 21 the mice were completely deprived of hair. Therefore a single dose of gene Fgf5go-Y does not affect alopecia mice homozygous for hr. However in double homozygotes Fgf5go-Y/Fgf5gO-hr/hr alopecia started 4 days later, namely on day 18. It usually finished 10-12 days after detection of first bald patches. On days 28-30 double homozygotes have lost all the hair. Hair loss in double homozygous mice was 1,5-fold slower than in +/+ hr/hr mice. This resulted from a significant extension of anagen phase induced by a mutant homozygous gene Fgf5go-Y in morphogenesis of the hair follicle. In contrast, hr gene was expressed only at the transmission phase from anagen to catagen. Our data shows that the angora gene is a modifier of the hairless gene and this results in a strong repression of alopecia progression in double homozygous mice compared to +/+ hr/hr animals.     

A Drosophila gene that is homologous to a mammalian gene associated with tumor metastasis codes for a nucleoside diphosphate kinase

The product of the abnormal wing discs (awd) gene of Drosophila is 78% identical to the product of the nm23 gene of mammals, which is differentially expressed in certain metastatic tumors. We present evidence that the awd gene codes for a nucleoside diphosphate kinase (NDP kinase) and that this Awd/NDP kinase is microtubule associated. Neuroblasts in Drosophila larvae homozygous for a null mutation in the awd gene are arrested in metaphase, indicating that microtubule-associated Awd/NDP kinase plays a critical role in spindle microtubule polymerization.     

A noncoding point mutation of Zeb1 causes multiple developmental malformations and obesity in Twirler mice

Heterozygous Twirler (Tw) mice develop obesity and circling behavior associated with malformations of the inner ear, whereas homozygous Tw mice have cleft palate and die shortly after birth. Zeb1 is a zinc finger protein that contributes to mesenchymal cell fate by repression of genes whose expression defines epithelial cell identity. This developmental pathway is disrupted in inner ears of Tw/Tw mice. The purpose of our study was to comprehensively characterize the Twirler phenotype and to identify the causative mutation. The Tw/+ inner ear phenotype includes irregularities of the semicircular canals, abnormal utricular otoconia, a shortened cochlear duct, and hearing loss, whereas Tw/Tw ears are severely malformed with barely recognizable anatomy. Tw/+ mice have obesity associated with insulin-resistance and have lymphoid organ hypoplasia. We identified a noncoding nucleotide substitution, c.58+181G>A, in the first intron of the Tw allele of Zeb1 (Zeb1(Tw)). A knockin mouse model of c.58+181G>A recapitulated the Tw phenotype, whereas a wild-type knockin control did not, confirming the mutation as pathogenic. c.58+181G>A does not affect splicing but disrupts a predicted site for Myb protein binding, which we confirmed in vitro. In comparison, homozygosity for a targeted deletion of exon 1 of mouse Zeb1, Zeb1(ΔEx1), is associated with a subtle abnormality of the lateral semicircular canal that is different than those in Tw mice. Expression analyses of E13.5 Twirler and Zeb1(ΔEx1) ears confirm that Zeb1(ΔEx1) is a null allele, whereas Zeb1(Tw) RNA is expressed at increased levels in comparison to wild-type Zeb1. We conclude that a noncoding point mutation of Zeb1 acts via a gain-of-function to disrupt regulation of Zeb1(Tw) expression, epithelial-mesenchymal cell fate or interactions, and structural development of the inner ear in Twirler mice. This is a novel mechanism underlying disorders of hearing or balance.     

No superoxide dismutase activity of cellular prion protein in vivo

Prion diseases are characterized by the deposition of PrP(Sc), an abnormal form of the cellular prion protein PrP(C), which is encoded by the Prnp gene. PrP(C) is highly expressed on neurons and its function is unknown. Recombinant PrP(C) was claimed to possess superoxide dismutase (SOD) activity, and it was hypothesized that abrogation of this function may contribute to neurodegeneration in prion diseases. We tested this hypothesis in vivo by studying copper/zinc and manganese SOD activity in genetically defined crosses of mice lacking the Sod1 gene with mice lacking PrP(C), and with hemizygous or homozygous tga20 transgenic mice overexpressing various levels of PrP(C). We failed to detect any influence of the Prnp genotype and gene dosage on SOD1 or SOD2 activity in heart, spleen, brain, and synaptosome-enriched brain fractions. Control experiments included crosses of mice lacking or overexpressing PrPc with mice overexpressing human Cu2+/Zn2+-superoxide dismutase, and confirmed that SOD enzymatic activity correlated exclusively with the gene dosage of bona fide human or murine SOD. We conclude that PrP(C) in vivo does not discernibly contribute to total SOD activity and does not possess an intrinsic dismutase activity.