Spatiotemporal expression of otogelin in the developing and adult mouse inner ear

Using a PCR-based subtractive method on cDNA from 2-day-old mouse cochlea, we identified a gene encoding otogelin, Otog, an inner ear specific glycoprotein expressed in all acellular structures. Here, we provide evidence that otogelin is detected as early as embryonic day 10 in the otic vesicle. At this stage, otogelin is detected in the epithelial cells which do not overlap with the myosin VIIA-expressing cells, namely the precursors of the hair cells, thus arguing for an early commitment of the two cell populations. Analysis of otogelin spatiotemporal cell distribution allows a molecular tracing for the contribution of the cochlear and vestibular inner ear supporting cells to the formation of the acellular structures. Throughout embryonic and adult life, the expression of the otogelin gene as monitored by LacZ inserted into Otog, and the abundance of the protein are greater in the vestibule than in the cochlea. In adult, otogelin is still produced by the vestibular supporting cells, which argues for a continuous process of otogelin renewal in the otoconial membranes and cupulae. In contrast, in the tectorial membrane, otogelin should be a long-lasting protein since both the otogelin gene and protein were almost undetectable in adult cochlear cells. The data are consistent with the requirement for otogelin in the attachment of the otoconial membranes and cupulae to their corresponding sensory epithelia as revealed in Otog -/- mice.

Targeted disruption of otog results in deafness and severe imbalance

Genes specifically expressed in the inner ear are candidates to underlie hereditary nonsyndromic deafness. The gene Otog has been isolated from a mouse subtractive cDNA cochlear library. It encodes otogelin, an N-glycosylated protein that is present in the acellular membranes covering the six sensory epithelial patches of the inner ear: in the cochlea (the auditory sensory organ), the tectorial membrane (TM) over the organ of Corti; and in the vestibule (the balance sensory organ), the otoconial membranes over the utricular and saccular maculae as well as the cupulae over the cristae ampullares of the three semi-circular canals. These membranes are involved in the mechanotransduction process. Their movement, which is induced by sound in the cochlea or acceleration in the vestibule, results in the deflection of the stereocilia bundle at the apex of the sensory hair cells, which in turn opens the mechanotransduction channels located at the tip of the stereo-cilia. We sought to elucidate the role of otogelin in the auditory and vestibular functions by generating mice with a targeted disruption of Otog. In Otog-/- mice, both the vestibular and the auditory functions were impaired. Histological analysis of these mutants demonstrated that in the vestibule, otogelin is required for the anchoring of the otoconial membranes and cupulae to the neuroepithelia. In the cochlea, ultrastructural analysis of the TM indicated that otogelin is involved in the organization of its fibrillar network. Otogelin is likely to have a role in the resistance of this membrane to sound stimulation. These results support OTOG as a possible candidate gene for a human nonsyndromic form of deafness.

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Localization and expression analysis of a novel conserved brain expressed transcript, Brx/BRX, lying within the Xic/XIC candidate region

The X inactivation center candidate region (Xic/XIC in mouse and human) is poorly characterized for the presence of transcription units. Only two conserved genes have been isolated to date, Xist/XIST and Cdx4/CDX4. The other known gene lying within this region, Tsx, has been identified so far only in rodents by analyzing the complete genomic sequence of a 94-kb region distal to Xist. Here, we report the characterization of an additional gene lying within this 94-kb sequenced region. Brx, for Brain X-linked gene, is a rare transcript preferentially expressed in the brain. It is normally X-inactivated in the mouse. Localisation of BRX, its human homolog has shown the gene to be located within the orthologous but inverted human CDX4-XIST segment. These results suggest that the gene order of the region encompassing the Cdx4-Xist interval in the mouse is similar in human. Comparison of the Xist-Brx and Brx-Cdx4 regions in mouse and human indicates that these intervals are three times longer in human than in mouse. BRX is a new potential candidate for one of the X-linked mental retardation syndromes mapped within the pericentromeric region of the human X Chromosome (Chr).

A 94 kb genomic sequence 3' to the murine Xist gene reveals an AT rich region containing a new testis specific gene Tsx

X chromosome inactivation in both mouse and human requires the presence of a cis acting locus, the X inactivation centre. This locus is thought to be involved in the initiation and spreading of the inactivation signal in early development. In order to increase our understanding of the mouse X inactivation centre, a 94 kb region immediately distal to the Xist gene has been sequenced and analysed for the presence of transcription units and/or potential cis acting regulatory elements. We have identified a novel gene, Tsx, lying 40 kb 3' from Xist. Tsx is expressed specifically in the testis and shows no convincing homology to proteins currently in the databases. A rat homologue, also X linked, has been isolated. The mouse and rat Tsx sequences are highly divergent, suggesting that part of the X inactivation centre, including both Xist and Tsx are subject to relatively weak evolutionary constraints.

Mapping the murine Xce locus with (CA)n repeats

The X Chromosome (Chr) controlling element locus (Xce) in the mouse has been shown to influence the X inactivation process. Xce maps to the central region of the X Chr, which also contains the Xist sequence, itself possibly implicated in the X inactivation process. Three microsatellite markers spanning the Xist locus have been isolated from an Xist containing YAC. All three microsatellite markers showed complete linkage with Xce in recombinants for the central span of the mouse X Chr between Ta and Moblo and strong linkage disequilibrium with Xce in all but one of the inbred mouse strains tested. In the standard Xceb typing strain JU/Ct, the two microsatellites most closely flanking Xist fail to carry the allelic forms expected if Xist and Xce are synonymous. Alternative explanations for this finding are presented in the context of our search for understanding the relation between Xist and Xce.

Physical mapping and YAC contig analysis of the region surrounding Xist on the mouse X chromosome

The Xist sequence has been proposed as a potential candidate for the X-inactivation center based both on its localization within the candidate region for the X-inactivation center in man and mouse and on its unique pattern of expression from the inactive X chromosome. We have cloned 550 kb of DNA surrounding the mouse Xist sequence in contiguously overlapping YAC clones and have developed a long-range restriction map that spans almost 1 Mb of this region and includes this YAC contig. The detailed restriction map we have established provides a framework for the identification of expressed sequences other than Xist that may equally exhibit unusual expression characteristics associated with X inactivation. The presence of possible structural or methylation differences within this region between the active and inactive X chromosomes has been investigated through comparative analysis of male and female genomic DNA, and we report here the identification of certain CpG-containing restriction sites around Xist that have an interesting differential methylation status on the inactive and active X chromosomes.

Adaptation of the interspersed repetitive sequence polymerase chain reaction to the isolation of mouse DNA probes from somatic cell hybrids on a hamster background

A strategy for the rapid isolation of DNA probes from radiation-fusion Chinese hamster cell hybrids containing overlapping portions of the murine X chromosome based on the interspersed repetitive sequence polymerase chain reaction (IRS-PCR) previously used with human somatic cell hybrids has been developed. This specific amplification of mouse DNA on a hamster background depends on the use of primers directed to the B2 short interspersed repeat element family and the R repeat, from the long interspersed repeat element family, L1. Two sets of amplification conditions, which gave specific amplification of mouse DNA from either a mouse X-monochromosomal hybrid or irradiation-fusion hybrids having reduced X content, were defined. The mouse X-only chromosome hybrid yielded approximately 20 discrete reproducible bands, while the irradiation-fusion hybrids yielded between 1 and 10 discrete products. Comparison of different irradiation-fusion hybrids has allowed the definition of both specific and shared products corresponding to different regions within the overlapping X-chromosome fragments present within these hybrids. Use of such hybrids and the IRS-PCR technique has allowed the isolation of probes corresponding to the central region of the mouse X chromosome that contains the X-inactivation center. The method should be widely applicable to the isolation of mouse DNA sequences from mouse hybrid cell lines on either human or Chinese hamster backgrounds.

Characterization of a murine gene expressed from the inactive X chromosome

In mammals, equal dosage of gene products encoded by the X chromosome in male and female cells is achieved by X inactivation. Although X-chromosome inactivation represents the most extensive example known of long range cis gene regulation, the mechanism by which thousands of genes on only one of a pair of identical chromosomes are turned off is poorly understood. We have recently identified a human gene (XIST) exclusively expressed from the inactive X chromosome. Here we report the isolation and characterization of its murine homologue (Xist) which localizes to the mouse X inactivation centre region and is the first murine gene found to be expressed from the inactive X chromosome. Nucleotide sequence analysis indicates that Xist may be associated with a protein product. The similar map positions and expression patterns for Xist in mouse and man suggest that this gene may have a role in X inactivation.

Characterization of the central region containing the X-inactivation center and terminal region of the mouse X chromosome using irradiation and fusion gene transfer hybrids

The irradiation and fusion gene transfer (IFGT) procedure provides a means of isolating subchromosomal fragments for use in the mapping of loci and for cloning probes from a particular area of a chromosome. Using this procedure, two large panels of somatic cell hybrids that contain mouse X Chromosome (Chr) fragments have been generated. These hybrid panels were generated by irradiating the monochromosomal mouse-hamster hybrid HYBX, which retains the mouse X Chr, with either 10 K or 50 K rads of X-irradiation followed by fusion with a recipient Chinese hamster cell line. IFGT hybrids retaining mouse material were generated at high frequency. These hybrids were used to orient loci in the X-inactivation center region that had not been resolvable in our interspecies backcross panel and also to map, within the terminal region of the X Chr, repeat elements detected by the probe p15-4. These hybrids not only complement existing interspecies meiotic mapping panels for the detailed analysis of specific regions of particular chromosomes, but also provide a potential source of material for chromosome-specific probe isolation.

Genetic and molecular evidence of an X-chromosome deletion spanning the tabby (Ta) and testicular feminization (Tfm) loci in the mouse

A new radiation-induced mutation in the mouse, tabby-25H (Ta25H), has proved to be a deletion which spans both the tabby and testicular feminization (Tfm) loci on the X chromosome. The Ta phenotype closely resembles that of the original TaFa mutation in both the heterozygous and hemizygous conditions but Ta25H/Y animals additionally show the Tfm/Y phenotype, being externally female but possessing abdominally located testes. There is a shortage of both Ta25H/+ and Ta25H/Y classes relative to their normal sibs among the progeny of Ta25H/+ females at weaning age and this was indicated to be due to prenatal or neonatal losses. Exencephaly was observed in some members of both classes prior to birth. Both Ta25H classes tend to be runted at weaning but, remarkably, Ta25H/+ females often show a range of abnormalities not evident in Ta25H/Y animals. When probes for the Zfx, Ccg-1, Phk, and DXPas19 loci, which lie close to Ta, were hybridised to DNAs from Ta25H hemizygotes, the profiles of the X-linked bands were similar to those of control DNAs, suggesting these loci lie outside the deletion. However, a clear absence of an X-linked band was found with human androgen receptor probes, indicating that the Tfm locus is indeed missing. The deletion, therefore, extends a minimum of 1.5 cM and, with its proximal and distal boundaries partially defined, it could be as large as 4 cM. As Ta25H/+ females show the striped X-inactivation coat pattern, the putative X-inactivation centre, Xce, which lies close to Ta, cannot be located within the region deleted. The greasy (Gs) locus similarly appears to lie outside the deletion.

Isolation of sequences from Xp22.3 and deletion mapping using sex chromosome rearrangements from human X-Y interchange sex reversals

A repeated DNA element (STIR) interspersed in Xp22.3 and on the Y chromosome has been used as a tag to isolate seven single-copy probes from the human sex chromosomes. The seven probes detect X-specific loci located in Xp22.3. Using a panel of X-chromosomal deletions from X-Y interchange sex reversals (XX males and XY females), these X-specific loci and some additional ones were mapped to four contiguous intervals of Xp22.3, proximal to the pseudoautosomal region and distal to STS. The construction of this deletion map of the terminal part of the human X chromosome can serve as a starting point for a long-range physical map of Xp22.3 and for a more accurate mapping of genetic diseases located in Xp22.3.

A sex chromosome rearrangement in a human XX male caused by Alu-Alu recombination

Human XX maleness is often due to the presence of Y-specific DNA, resulting from abnormal interchange of terminal parts of the short arms of the X and Y chromosomes. In an XX male, a rearrangement is observed at locus DXYS5, the most proximal Yp locus detected in this patient. Cloning and analysis of the rearranged DNA fragment revealed pseudoautosomal sequences located beyond the breakpoint. We propose that this XX male arose by abnormal crossing over between DXYS5 on the Y chromosome and a pseudoautosomal locus on the X chromosome during paternal meiosis. Sequence analysis of the junction shows that homologous recombination occurred between two Alu sequences from these otherwise nonhomologous regions. The site of recombination is localized to the putative transcription promoter region of the Alu sequences.

Two highly polymorphic minisatellites from the pseudoautosomal region of the human sex chromosomes

Two pseudoautosomal loci DXYS15 and DXYS17 from the pairing region of the human sex chromosomes display a high variability with at least eight alleles each. The structural elements responsible for the polymorphisms have been isolated and sequenced. In both cases the variations result from DNA rearrangements occurring in tandemly repeated sequences (minisatellites) of 21-29 nucleotides for DXYS15 and 28-33 nucleotides for DXYS17. At reduced stringency, the DXYS15 minisatellite detects other hypervariable sequences located in other parts of the genome and hence represents a new family of minisatellites. In contrast to most other known hypervariable families, the DXYS15 hypervariable sequence displays a very high AT content.

A deletion map of the human Y chromosome based on DNA hybridization

The genomes of 27 individuals (19 XX males, two XX hermaphrodites, and six persons with microscopically detectable anomalies of the Y chromosome) were analyzed by hybridization for the presence or absence of 23 Y-specific DNA restriction fragments. Y-specific DNA was detected in 12 of the XX males and in all six individuals with microscopic anomalies. The results are consistent with each of these individuals carrying a single contiguous portion of the Y chromosome; that is, the results suggest a deletion map of the Y chromosome, in which each of the 23 Y-specific restriction fragments tested can be assigned to one of seven intervals. We have established the polarity of this map with respect to the long and short arms of the Y chromosome. On the short arm, there is a large cluster of sequences homologous to the X chromosome. The testis determinant(s) map to one of the intervals on the short arm.

A gradient of sex linkage in the pseudoautosomal region of the human sex chromosomes

Three independent pseudoautosomal loci are linked to sex determination at frequencies which define a gradient of linkage. The segregation patterns of these loci indicate that X/Y recombination results from a single obligatory meiotic crossing-over in the pseudoautosomal region. Recombination in male germ cells in the terminal regions of the short arms of the X and Y chromosomes in 10-fold greater than between the same regions of the X chromosomes in female germ cells.

Pseudoautosomal DNA sequences in the pairing region of the human sex chromosomes

A DNA probe from a human Y chromosome-derived cosmid detects a single-copy genomic DNA fragment which can appear in different allelic forms shared by both sex chromosomes. Variants at this DNA locus show an autosomal pattern of inheritance, undergo recombination with sexual phenotype and can therefore be described as 'pseudoautosomal'. Another probe from the same cosmid detects a sequence repeated 15-20 times per haploid genome. These repeats also appear pseudoautosomal and map exclusively to the short-arm terminal region of each sex chromosome.

Minor histocompatibility antigens are developmentally regulated on murine embryonal carcinoma cells and their early differentiated derivatives

Differences in the expression of minor histocompatibility (Hm) alloantigens on two mouse embryonal carcinoma (EC) cell lines and the PYS-2 and T.D.M.-1 differentiated derivatives have been demonstrated by their ability to elicit a cytolytic T lymphocyte response. Experiments involving the use of various responder-target strain combinations and recombinant inbred mice strains have shown that: (1) there are major differences in Hm expression on EC cells compared with differentiated derivatives whose Hm expression appears more like that of adult splenocytes; (2) although both EC cell lines show reduced Hm immunogenicity compared with adult splenocytes, major differences in the expression and possible presentation of Hm between the F9 and PCC3 EC cell lines can be detected by in vivo priming and by in vitro cold competition target experiments. These observations are discussed in relation to the differences in allograft rejection patterns observed with PCC3 and F9 and to possible differences in developmental staging of these cell lines.

Differential Hm antigen expression on EC cells and early differentiated derivatives

Differences in the expression of minor histocompatibility (Hm) alloantigens on two mouse embryonal carcinoma (EC) cell lines and the PYS-2 and T.D.M.-1 differentiated derivatives have been demonstrated by their ability to elicit a cytolytic T-lymphocyte (CTL) response. Experiments involving the use of various responder-target strain combinations on the one hand and Recombinant Inbred (RI) mice strains on the other have shown that: (i) there are major differences in Hm expression on the EC cells compared with the differentiated derivatives whose Hm expression appears more akin to that of adult splenocytes; (ii) although both EC cell lines show reduced Hm immunogenicity compared with adult splenocytes, major differences in the expression and possibly presentation between the F9 and PCC3 EC cell lines can be detected both by in vivo priming and by in vitro cold competition target experiments. These results are discussed in connection with the unexpected finding that some EC cell lines are capable of specific competition effects for appropriate CTL effectors despite their inability to stimulate such effectors in vitro and the absence of major histocompatibility complex (MHC) products.

The significance of natural killer activity in the resistance of allogeneic hosts to the embryonal carcinoma cell line F9

A number of mouse strains of known F9 resistance phenotype have been tested for their in vitro natural killer activity against both F9 and YAC target cells. The pattern of in vitro natural killer activity observed does not correlate with the pattern of in vivo F9 resistance. The relative efficiencies of in vitro lysis of the F9 and YAC targets by endogenous natural killer effectors from the 129/Sv, SJL/J, C57Bl/6J, and BALB/cJ strains do, however, parallel each other, even though overall levels of F9 target lysis are very low. Since cold competition experiments indicate that the embryonal carcinoma cell lines tested, F9, PCC4/Aza, and PCC3/A/1, can compete efficiently with YAC as target, this low lysis of embryonal carcinoma cells may be due to an intrinsic lysis resistance. The finding that the parietal endoderm cell line PYS-2 and the trophoectodermal cell line TDM1 also compete with YAC targets in cold competition experiments is discussed in relation to previous reports suggesting that such differentiated derivatives lack natural killer target structures.

Genetics of teratocarcinoma transplantation. III. Genetic control of resistance to F9 tumor formation in allogeneic hosts

Major F9 allograft resistance of strains C57Bl/6J, CBA/J, C3H/He and AKR/J has been shown to be controlled by a small number of recessive genes. These loci are not linked to H-2. Recombinational analysis suggests that the loci responsible for resistance in these strains are at least partially non-overlapping. These results obtained with the blocked F9 embryonal carcinoma cell line are discussed in relation to those reported for embryonal carcinoma strain PCC3/A/l and OTT6050 embryoid bodies, where recessive resistance is H-2 linked.

Accessory cells in the in vitro generation of type C virus-specific T killer lymphocytes. II. Demonstration of a T helper cell in the spleen of in vivo primed mice

The existence of a helper T cell cooperating with cytolytic T lymphocytes (CTL) in cell-mediated anti-tumor responses specific for the virus-induced FMR antigens can be demonstrated by using unprimed thymocytes as CTL precursors and in vivo primed irradiated spleen cells as helper. The helper T cells express Thy-1.2 and Lyt-1.2 antigens at their surface, but not Lyt-2.2. The helper function required the presence of macrophages to be detected, is antigen specific, and appears unusually radiosensitive compared with previously described helper T cell function.

Accessory cells in the in vitro generation of type C virus-specific T killer lymphocytes. II. Demonstration of a T helper cell in the spleen of in vivo primed mice

The existence of a helper T cell cooperating with cytolytic T lymphocytes (CTL) in cell-mediated anti-tumor responses specific for the virus-induced FMR antigens can be demonstrated by using unprimed thymocytes as CTL precursors and in vivo primed irradiated spleen cells as helper. The helper T cells express Thy-1.2 and Lyt-1.2 antigens at their surface, but not Lyt-2.2. The helper function required the presence of macrophages to be detected, is antigen specific, and appears unusually radiosensitive compared with previously described helper T cell function.

Comparison of the restoration effect of Pseudomonas aeruginosa, BCG and poly I: poly C on cancer patients non responsive to recall antigen delayed hypersensitivity

A preparation of 10 serotypes of Pseudomonas aeruginosa has restored skin delayed hypersensitivity reactions to recall antigens in about fifty per cent of cancer patients not previously immunodepressed by radiotherapy or chemotherapy, but anergic. This proportion is similar to that obtained by given modalities of administration of BCG, C. parvum or levamisole, while other modalities of application of BCG or administration of poly I: poly C do not induce such an immuno-restoration in a significant number of patients.

Modulation by alpha-2 macroglobulin of human lymphocyte proliferation in response to mitogens and antigen

The effect was studied of purified alpha-2 macroglobulin (a potent and polyvalent protease inhibitor) on normal human lymphocytes stimulated by phytohaemagglutinin, pokeweed mitogen, or by purified protein derivative as an antigen. At physiological concentration alpha 2 M has been found to inhibit mitogenic as well as antigenic stimulation. However at lower dilutions alpha 2 M acts in synergy either with the mitogen or with the antigen. At these dilutions thymidine incorporation is enhanced. alpha 2 M has no toxic or mitogenic effect on normal human lymphocytes. These data might indicate that two proteases may play a role in the proliferation of normal human lymphocytes.

Monitoring of nonspecific cell-mediated immunity in cancer patients. I. Frequent dissociation between the responses of skin tests to recall antigens and in vitro lymphocyte transformation

No correlation was found between in vivo delayed hypersensitivity responses in cancer patients and in vitro lymphocyte transformation by mitogens or antigens, even when the same antigen [purified protein derivative of tuberculin (PPD)] was used for both the in vivo and in vitro testing. However, there was a good correlation between the in vitro lymphocyte transformation tests with PPD and with the mitogens phytohemagglutinin and pokeweed mitogen.

Cell-mediated immune responsiveness of patients with acute lymphocytic leukemia in remission

Children with acute lymphocytic leukemia (ALL) in remission and undergoing either chemotherapy or immunotherapy were tested for general cell-mediated immunocompetence and cell-mediated reactivity to tumor-associated antigens (TAA) using the following parameters: skin tests with recall antigens and extracts of lymphoblastoid cell lines; primary sensitization to dinitrofluorobenzene and picryl chloride; in vitro tranformation by mitogens and PPD; and lymphocyte-mediated cytotoxicity against a lymphoblastoid cell line and a panel of cryopreserved leukemic blasts. Reactivity in all assays of children on continuous chemotherapy was significantly depressed compared to similar patients later in the study. Patients on intermittent chemotherapy demonstrated much less immunodepression. The groups tested early during immunotherapy with BCG and allogeneic leukemic blasts were hyper-responsive (compared to published data) to primary sensitization with picryl chloride. Skin test reactivity to recall antigens and to tumor-derived lymphoblastoid cell lines was suppressed (as analyzed serial comparison) in this hyperimmunized group, possibly due to antigenic competition, and reactivity in all other assays was normal. The patients tested after 2-8 years of immunotherapy showed significantly higher positive skin-test responses to extracts of tumor-derived lymphoblastoid cell lines as compared to the other groups. The results of this multiphasic screen support the known effects of chemotherapy on immunocompetence. Moreover, they document the prompt return of immunocompetence with intermittent chemotherapy and during immuno-therapy. These results do not, however, indicate a striking augmentation of the immune response during immunotherapy as measured by these parameters.