Carcinoembryonic antigen-related cell adhesion molecule 10 expressed specifically early in pregnancy in the decidua is dispensable for normal murine development

The carcinoembryonic antigen (CEA) family consists of a large group of evolutionarily and structurally divergent glycoproteins. The murine CEACAM9 and CEACAM11-related proteins as well as the pregnancy-specific glycoproteins (PSG) are secreted members of the CEA family which are differentially expressed in fetal trophoblast cell populations during placental development. PSG are essential for a successful pregnancy, possibly by protecting the semiallotypic fetus from the maternal immune system. In contrast, Ceacam10 mRNA, coding for a protein identical in structure with CEACAM11-related proteins, is expressed in the maternal decidua surrounding the implantation site of the conceptus only during early stages of gestation between day 6.5 and day 10.5 postcoitum. To determine its role during murine development, we inactivated Ceacam10. Ceacam10(-/-) mice developed, like the previously established Ceacam9(-/-) mice, indistinguishably from wild-type littermates with respect to sex ratio, weight gain, and fertility. However, a small but significant reduction of the litter size by 23% was observed in Ceacam10(-/-) matings. Furthermore, combining the Ceacam9 and Ceacam10 null alleles, both located on chromosome 7, by meiotic recombination and subsequent mating of heterozygotes carrying both knockout alleles on one chromosome yielded wild-type and double knockout offspring at the expected Mendelian ratio. Taken together, both Ceacam10 and Ceacam9, alone or in combination, are not essential for either murine placental and embryonic development or for adult life.     

Age-related degradation of tectorial membrane dynamics with loss of CEACAM16

Studies of genetic disorders of sensorineural hearing loss have been instrumental in delineating mechanisms that underlie the remarkable sensitivity and selectivity that are hallmarks of mammalian hearing. For example, genetic modifications of TECTA and TECTB, which are principal proteins that comprise the tectorial membrane (TM), have been shown to alter auditory thresholds and frequency tuning in ways that can be understood in terms of changes in the mechanical properties of the TM. Here, we investigate effects of genetic modification targeting CEACAM16, a third important TM protein. Loss of CEACAM16 has been recently shown to lead to progressive reductions in sensitivity. Whereas age-related hearing losses have previously been linked to changes in sensory receptor cells, the role of the TM in progressive hearing loss is largely unknown. Here, we show that TM stiffness and viscosity are significantly reduced in adult mice that lack functional CEACAM16 relative to age-matched wild-type controls. By contrast, these same mechanical properties of TMs from juvenile mice that lack functional CEACAM16 are more similar to those of wild-type mice. Thus, changes in hearing phenotype align with changes in TM material properties and can be understood in terms of the same TM wave properties that were previously used to characterize modifications of TECTA and TECTB. These results demonstrate that CEACAM16 is essential for maintaining TM mechanical and wave properties, which in turn are necessary for sustaining the remarkable sensitivity and selectivity of mammalian hearing with increasing age.     

Targeted disruption of the Ceacam1 (MHVR) gene leads to reduced susceptibility of mice to mouse hepatitis virus infection

The CEACAM1 glycoproteins (formerly called biliary glycoproteins; BGP, C-CAM, CD66a, or MHVR) are members of the carcinoembryonic antigen family of cell adhesion molecules. In the mouse, splice variants of CEACAM1 have either two or four immunoglobulin (Ig) domains linked through a transmembrane domain to either a short or a long cytoplasmic tail. CEACAM1 has cell adhesion activity and acts as a signaling molecule, and long-tail isoforms inhibit the growth of colon and prostate tumor cells in rodents. CEACAM1 isoforms serve as receptors for several viral and bacterial pathogens, including the murine coronavirus mouse hepatitis virus (MHV) and Haemophilus influenzae, Neisseria gonorrhoeae, and Neisseria meningitidis in humans. To elucidate the mechanisms responsible for the many biological activities of CEACAM1, we modified the expression of the mouse Ceacam1 gene in vivo. Manipulation of the Ceacam1 gene in mouse embryonic stem cells that contained the Ceacam1a allele yielded a partial knockout. We obtained one line of mice in which the insert in the Ceacam1a gene had sustained a recombination event. This resulted in the markedly reduced expression of the two CEACAM1a isoforms with four Ig domains, whereas the expression of the two isoforms with two Ig domains was doubled relative to that in wild-type BALB/c (+/+) mice. Homozygous (p/p) Ceacam1a-targeted mice (Ceacam1aDelta4D) had no gross tissue abnormalities and were viable and fertile; however, they were more resistant to MHV A59 infection and death than normal (+/+) mice. Following intranasal inoculation with MHV A59, p/p mice developed markedly fewer and smaller lesions in the liver than +/+ or heterozygous (+/p) mice. The titers of virus produced in the livers were 50- to 100-fold lower in p/p mice than in +/p or +/+ mice. p/p mice survived a dose 100-fold higher than the lethal dose of virus for +/+ mice. +/p mice were intermediate between +/+ and p/p mice in susceptibility to liver damage, virus growth in liver, and susceptibility to killing by MHV. Ceacam1a-targeted mice provide a new model to study the effects of modulation of receptor expression on susceptibility to MHV infection in vivo.     

Ceacam1a-/- mice are completely resistant to infection by murine coronavirus mouse hepatitis virus A59

CEACAM1a glycoproteins are members of the immunoglobulin (Ig) superfamily and the carcinoembryonic antigen family. Isoforms expressing either two or four alternatively spliced Ig-like domains in mice have been found in a number of epithelial, endothelial, or hematopoietic tissues. CEACAM1a functions as an intercellular adhesion molecule, an angiogenic factor, and a tumor cell growth inhibitor. Moreover, the mouse and human CEACAM1a proteins are targets of viral or bacterial pathogens, respectively, including the murine coronavirus mouse hepatitis virus (MHV), Haemophilus influenzae, Neisseria gonorrhoeae, and Neisseria meningitidis, as well as Moraxella catarrhalis in humans. We have shown that targeted disruption of the Ceacam1a (MHVR) gene resulting in a partial ablation of the protein in mice (p/p mice) led to reduced susceptibility to MHV-A59 infection of the modified mice in the BALB/c background. We have now engineered and produced a Ceacam1a-/- mouse that exhibits complete ablation of the CEACAM1a protein in every tissue where it is normally expressed. We report that 3-week-old Ceacam1a-/- mice in the C57BL/6 genetic background are fully resistant to MHV-A59 infection by both intranasal and intracerebral routes. Whereas virus-inoculated wild-type +/+ C57BL/6 mice showed profound liver damage and spinal cord demyelination under these conditions, Ceacam1a-/- mice displayed normal livers and spinal cords. Virus was recovered from liver and spinal cord tissues of +/+ mice but not of -/- mice. These results indicate that CEACAM1a is the sole receptor for MHV-A59 in both liver and brain and that its deletion from the mouse renders the mouse completely resistant to infection by this virus.     

Molecular cloning and localization of a CEACAM2 isoform,CEACAM2‐L,expressed in spermatids in mouse testis

Carcinoembryonic antigen (CEA) family, a subgroup of the immunoglobulin (Ig) superfamily, is divided into two sub‐families: the CEA‐related cell adhesion molecules (CEACAM) and the pregnancy‐specific glycoproteins. The isoform CEACAM2 is expressed in mouse testis; in this study, we identified a novel isoform of Ceacam2, Ceacam2‐Long (Ceacam2‐L). CEACAM2‐L is different from CEACAM2 in that it has much longer cytoplasmic tail region. Ceacam2‐L starts to appear faintly in mouse testis after 3 weeks of postnatal development, and its expression level increased after 5 weeks. Immunoblot analysis confirmed the expression of CEACAM2‐L in the seminiferous epithelium of mouse testis. Immunohistochemical data showed that CEACAM2‐L was not observed on spermatogonia, spermatocytes, round spermatids, or Sertoli cells, but was seen at the plasma membrane of elongating spermatids in contact with extended cytoplasmic processes of Sertoli cells. CEACAM2‐L was not detected at the head region of elongating spermatids, where the apical ectoplasmic specialization is constructed. These data suggest that CEACAM2‐L might be a novel adhesion molecule contributing to cell‐to‐cell adhesion between elongating spermatids and Sertoli cells within the seminiferous epithelium. Mol. Reprod. Dev. 79: 843–852, 2012. © 2012 Wiley Periodicals, Inc.     

Increased Osteoclastogenesis in Mice Lacking the Carcinoembryonic Antigen-Related Cell Adhesion Molecule 1

Alterations in bone remodeling are a major public health issue, as therapeutic options for widespread bone disorders such as osteoporosis and tumor-induced osteolysis are still limited. Therefore, a detailed understanding of the regulatory mechanism governing bone cell differentiation in health and disease are of utmost clinical importance. Here we report a novel function of carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1), a member of the immunoglobulin superfamily involved in inflammation and tumorigenesis, in the physiologic regulation of bone remodeling. Assessing the expression of all members of the murine Ceacam family in bone tissue and marrow, we found CEACAM1 and CEACAM10 to be differentially expressed in both bone-forming osteoblasts and bone-resorbing osteoclasts. While Ceacam10-deficient mice displayed no alteration in structural bone parameters, static histomorphometry demonstrated a reduced trabecular bone mass in mice lacking CEACAM1. Furthermore, cellular and dynamic histomorphometry revealed an increased osteoclast formation in Ceacam1-deficient mice, while osteoblast parameters and the bone formation rate remained unchanged. In line with these findings, we detected accelerated osteoclastogenesis in Ceacam1-deficient bone marrow cells, while osteoblast differentiation, as determined by mineralization and alkaline phosphatase assays, was not affected. Therefore, our results provide in vivo and in vitro evidence for a physiologic role of CEACAM1 in the regulation of osteoclastogenesis.     

Identification of CEACAM6 as an intermediate filament-associated protein expressed in Sertoli cells of rat testis

Ceacam6 (carcinoembryonic antigen-related cell adhesion molecule 6 gene) has recently been isolated by differential display followed by RT-PCR and DNA sequence analyses. Ceacam6 is a member of an immunoglobulin superfamily and encodes a protein of 266 amino acid residues possessing one immunoglobulin (Ig)-like domain. RT-PCR analysis showed that Ceacam6 was dominantly expressed in rat testis and its expression level prominently increased after 6 wk of postnatal development in testis. Immunohistochemical analyses using the anti-CEACAM6 antibody revealed that CEACAM6 colocalized with intermediate filaments (vimentin) in Sertoli cells and interstitial cells. The association between CEACAM6 and vimentin was observed throughout postnatal development in rat testis. Transfection experiments performed in COS-7 cells suggested that overexpression of CEACAM6 brought about aggregation of vimentin filament around nuclei with which CEACAM6 colocalized and that the N-terminus region of CEACAM6, including the Ig-like domain, seemed to be required for association with vimentin filaments. Interaction between CEACAM6 and vimentin in rat testis and transfected COS-7 cells was confirmed by immunoprecipitation. Our observations strongly suggested that CEACAM6 might be a novel intermediate filament-associated protein involved in regulation of vimentin architecture in Sertoli cells.     

Intron retention generates a novel isoform of CEACAM6 that may act as an adhesion molecule in the ectoplasmic specialization structures between spermatids and sertoli cells in rat testis

By differential display technique followed by RT-PCR and DNA sequence analyses, we isolated carcinoembryonic antigen-related cell adhesion molecule 6 (Ceacam6) and its novel spliced variant Ceacam6-Long (Ceacam6-L) from rat testis. Ceacam6-L mRNA was generated by retention of 67 nucleotide-length third intron in Ceacam6 gene. Ceacam6-L is a member of an immunoglobulin superfamily and encodes a protein of 50 kDa with a signal sequence at the N-terminus, one immunoglobulin (Ig)-like domain, three IgCAM domains, a transmembrane region, and a short intracellular region. Expression analyses by RT-PCR and Northern blot showed that Ceacam6-L was exclusively expressed in rat testis and first detectable at 5 wk during postnatal development of testis. We performed immunoblot analyses and immunohistochemistry using the anti-CEACAM6-L antibody. Confocal laser scanning microscopy revealed that CEACAM6-L was not present at blood-testis barrier junctions between Sertoli cells but localized at the interface between Sertoli cells and germ cells, possibly to work as an adhesion molecule in the apical compartment of the seminiferous epithelium. At stages VII-VIII, at which all of the elongated spermatids migrated to the luminal surface of the seminiferous tubules, CEACAM6-L was found to locate at the concave side of elongated spermatid heads, following the curvature of their sickle-shaped nuclei, suggesting that CEACAM6-L might be involved in the anchoring of spermatids to Sertoli cells and spermiation. We concluded that CEACAM6-L might be a novel adhesion molecule constructing the apical ectoplasmic specialization in testis.     

Demonstration of a glycoprotein derived from the Ceacam10 gene in mouse seminal vesicle secretions

CEACAM10 was purified from mouse seminal vesicle secretions by a series of purification steps that included ion exchange chromatography on a DEAE-Sephacel column and ion exchange high-performance liquid chromatography on a sulfopropyl column. It was shown to be a 36-kDa glycoprotein with an N-linked carbohydrate moiety. The circular dichromoism spectrum of CEACAM10 in 50 mM phosphate buffer at pH 7.4 appeared as one negative band arising from the beta form at 217 nm. CEACAM10 was expressed predominantly in seminal vesicles of adult mice. Both CEACAM10 and its mRNA were demonstrated on the luminal epithelium of the mucosal folds in the seminal vesicle. The amount of Ceacam10 mRNA in the seminal vesicle was correlated with the stage of animal maturation. Castration of adult mice resulted in cessation of Ceacam10 expression, while treatment of castrated mice with testosterone propionate in corn oil restored Ceacam10 expression in the seminal vesicle. During the entire course of pregnancy, Ceacam10 might be silent in the embryo. A cytochemical study illustrated the presence of the CEACAM10 binding region on the entire surface of mouse sperm. CEACAM10-sperm binding greatly enhanced sperm motility in vitro.     

Perturbation of Lytic and Latent Gammaherpesvirus Infection in the Absence of the Inhibitory Receptor CEACAM1

Control of gammaherpesvirus infections requires a complex, well orchestrated immune response regulated by positive and negative co-signaling molecules. While the impact of co-stimulatory molecules has been addressed in various studies, the role of co-inhibitory receptors has not been tested. The ITIM-bearing CEACAM1 is an inhibitory receptor expressed by a variety of immune cells, including B, T and NK cells. Using Ceacam1^−/− mice, we analyzed the in vivo function of CEACAM1 during acute and latent murine gammaherpesvirus 68 (MHV-68) infection. During acute lytic replication, we observed lower virus titers in the lungs of Ceacam1^−/− mice than in WT mice. In contrast, during latency amplification, Ceacam1^−/− mice displayed increased splenomegaly and a higher latent viral load in the spleen. Analysis of the immune response revealed increased virus-specific antibody levels in Ceacam1^−/− mice, while the magnitude of the T cell-mediated antiviral immune response was reduced. These findings suggest that inhibitory receptors can modulate the efficacy of immune responses against gammaherpesvirus infections.     

Regulation of the Epithelial Adhesion Molecule CEACAM1 Is Important for Palate Formation

Cleft palate results from a mixture of genetic and environmental factors and occurs when the bilateral palatal shelves fail to fuse. The objective of this study was to search for new genes involved in mouse palate formation. Gene expression of murine embryonic palatal tissue was analyzed at various developmental stages before, during, and after palate fusion using GeneChip® microarrays. Ceacam1 was one of the highly up-regulated genes during palate formation, and this was confirmed by quantitative real-time PCR. Immunohistochemical staining showed that CEACAM1 was present in prefusion palatal epithelium and was degraded during fusion. To investigate the developmental role of CEACAM1, function-blocking antibody was added to embryonic mouse palate in organ culture. Palatal fusion was inhibited by this function-blocking antibody. To investigate the subsequent developmental role of CEACAM1, we characterized Ceacam1-deficient (Ceacam1 ^−/−) mice. Epithelial cells persisted abnormally at the midline of the embryonic palate even on day E16.0, and palatal fusion was delayed in Ceacam1 ^−/− mice. TGFβ3 expression, apoptosis, and cell proliferation in palatal epithelium were not affected in the palate of Ceacam1^−/−mice. However, CEACAM1 expression was retained in the remaining MEE of TGFβ-deficient mice. These results suggest that CEACAM1 has roles in the initiation of palatal fusion via epithelial cell adhesion.     

PPARα (Peroxisome Proliferator-activated Receptor α) Activation Reduces Hepatic CEACAM1 Protein Expression to Regulate Fatty Acid Oxidation during Fasting-refeeding Transition

Carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) is expressed at high levels in the hepatocyte, consistent with its role in promoting insulin clearance in liver. CEACAM1 also mediates a negative acute effect of insulin on fatty acid synthase activity. Western blot analysis reveals lower hepatic CEACAM1 expression during fasting. Treating of rat hepatoma FAO cells with Wy14,643, an agonist of peroxisome proliferator-activated receptor α (PPARα), rapidly reduces Ceacam1 mRNA and CEACAM1 protein levels within 1 and 2 h, respectively. Luciferase reporter assay shows a decrease in the promoter activity of both rat and mouse genes by Pparα activation, and 5′-deletion and block substitution analyses reveal that the Pparα response element between nucleotides −557 and −543 is required for regulation of the mouse promoter activity. Chromatin immunoprecipitation analysis demonstrates binding of liganded Pparα to Ceacam1 promoter in liver lysates of Pparα^+/+, but not Pparα^−/− mice fed a Wy14,643-supplemented chow diet. Consequently, Wy14,643 feeding reduces hepatic Ceacam1 mRNA and CEACAM1 protein levels, thus decreasing insulin clearance to compensate for compromised insulin secretion and maintain glucose homeostasis and insulin sensitivity in wild-type mice. Together, the data show that the low hepatic CEACAM1 expression at fasting is mediated by Pparα-dependent mechanisms. Changes in CEACAM1 expression contribute to the coordination of fatty acid oxidation and insulin action in the fasting-refeeding transition.     

Carcinoembryonic antigen-related cell adhesion molecule 1 expression and signaling in human, mouse, and rat leukocytes: evidence for replacement of the short cytoplasmic domain isoform by glycosylphosphatidylinositol-linked proteins in human leukocytes

Carcinoembryonic Ag-related cell adhesion molecule 1 (CEACAM1), the primordial carcinoembryonic Ag gene family member, is a transmembrane cell adhesion molecule expressed in leukocytes, epithelia, and blood vessel endothelia in humans and rodents. As a result of differential splicing, CEACAM1 occurs as several isoforms, the two major ones being CEACAM1-L and CEACAM1-S, that have long (L) or short (S) cytoplasmic domains, respectively. The L:S expression ratios vary in different cells and tissues. In addition to CEACAM1, human but not rodent cells express GPI-linked CEACAM members (CEACAM5-CEACAM8). We compared the expression patterns of CEACAM1-L, CEACAM1-S, CEACAM6, and CEACAM8 in purified populations of neutrophilic granulocytes, B lymphocytes, and T lymphocytes from rats, mice, and humans. Human granulocytes expressed CEACAM1, CEACAM6, and CEACAM8, whereas human B lymphocytes and T lymphocytes expressed only CEACAM1 and CEACAM6. Whereas granulocytes, B cells, and T cells from mice and rats expressed both CEACAM1-L and CEACAM1-S in ratios of 2.2-2.9:1, CEACAM1-S expression was totally lacking in human granulocytes, B cells, and T cells. Human leukocytes only expressed the L isoforms of CEACAM1. This suggests that the GPI-linked CEACAM members have functionally replaced CEACAM1-S in human leukocytes. Support for the replacement hypothesis was obtained from experiments in which the extracellular signal-regulated kinases (Erk)1/2 were activated by anti-CEACAM Abs. Thus, Abs against CEACAM1 activated Erk1/2 in rat granulocytes, but not in human granulocytes. Erk1/2 in human granulocytes could, however, be activated by Abs against CEACAM8. We demonstrated that CEACAM1 and CEACAM8 are physically associated in human granulocytes. The CEACAM1/CEACAM8 complex in human cells might accordingly play a similar role as CEACAM1-L/CEACAM1-S dimers known to occur in rat cells.     

Increased Glucose-induced Secretion of Glucagon-like Peptide-1 in Mice Lacking the Carcinoembryonic Antigen-related Cell Adhesion Molecule 2 (CEACAM2)

Carcinoembryonic antigen-related cell adhesion molecule 2 (CEACAM2) regulates food intake as demonstrated by hyperphagia in mice with the Ceacam2 null mutation (Cc2^−/−). This study investigated whether CEACAM2 also regulates insulin secretion. Ceacam2 deletion caused an increase in β-cell secretory function, as assessed by hyperglycemic clamp analysis, without affecting insulin response. Although CEACAM2 is expressed in pancreatic islets predominantly in non-β-cells, basal plasma levels of insulin, glucagon and somatostatin, islet areas, and glucose-induced insulin secretion in pooled Cc2^−/− islets were all normal. Consistent with immunofluorescence analysis showing CEACAM2 expression in distal intestinal villi, Cc2^−/− mice exhibited a higher release of oral glucose-mediated GLP-1, an incretin that potentiates insulin secretion in response to glucose. Compared with wild type, Cc2^−/− mice also showed a higher insulin excursion during the oral glucose tolerance test. Pretreating with exendin(9–39), a GLP-1 receptor antagonist, suppressed the effect of Ceacam2 deletion on glucose-induced insulin secretion. Moreover, GLP-1 release into the medium of GLUTag enteroendocrine cells was increased with siRNA-mediated Ceacam2 down-regulation in parallel to an increase in Ca²⁺ entry through L-type voltage-dependent Ca²⁺ channels. Thus, CEACAM2 regulates insulin secretion, at least in part, by a GLP-1-mediated mechanism, independent of confounding metabolic factors.     

Gelsolin immunoreactivity and development of the tectorial membrane in the cochlea of normal and hypothyroid rats

Summary Gelsolin was localized by immunocytochemistry in the developing cochlea of the rat. In normal animals, the protein appeared at 18 th day in utero in cells of the Kölliker's organ, which are involved in the secretion of the tectorial membrane. The Kölliker's organ cells were not immunoreactive after the first postnatal week, which is when they cease their secretory activity. Gelsolin immunoreactivity was similar in thyroid-deficient rats until the second postnatal week but, at this age, Kölliker's organ did not transform and its gelsolin immunoreactivity persisted, together with its secretory activity. As a result, the tectorial membrane was greatly distorted and out of contact with the hair cells, which dramatically impaired the mechanical properties of the organ of Corti. The developing cochlea thus provides an example of the involvement of gelsolin in a secretory process that is of importance in the development of hearing.     

Soluble megalin is accumulated in the lumen of the rat endolymphatic sac

The endolymphatic sac (ES) is believed to play an important role in maintaining homeostasis in the inner ear by the absorption and endocytosis of endolymph. Megalin is a 600-kDa multiligand endocytic receptor expressed in certain types of absorptive epithelia including kidney proximal tubules. We analyzed the immunoreactivity for megalin in rat ES by immunofluorescence, immunogold electron microscopy, and immunoblotting. With immunostaining, the luminal substances of the ES were strongly stained for megalin. Megalin was also localized in luminal macrophage-like cells and both types of epithelial cell (mitochondria-rich cells and ribosome-rich cells). In these cells, the megalin was localized in the lumen of endosomes, but was not membrane associated. This localization pattern indicates that the megalin in these cells is not a membrane receptor, but merely one of the constituents that are endocytosed from the lumen of the ES. Immunoblotting indicated that the megalin in the ES is a 210-kDa molecule lacking a cytoplasmic domain. This suggests that the megalin in the ES may be a soluble form, different from the 600-kDa membrane-bound receptor expressed in kidneys. Taken together, it is likely that the megalin in the ES lumen is a soluble component and may be endocytosed by the ES epithelial cells. Furthermore, we found that the tectorial membrane, an acellular structure in the cochlea, gave a strong megalin immunoreaction. Since the cochlea is connected to the ES, the megalin may be transported alone or with the components of the tectorial membrane from the cochlea to the ES lumen through longitudinal flow.     

Orphan glutamate receptor delta1 subunit required for high-frequency hearing

The function of the orphan glutamate receptor delta subunits (GluRdelta1 and GluRdelta2) remains unclear. GluRdelta2 is expressed exclusively in the Purkinje cells of the cerebellum, and GluRdelta1 is prominently expressed in inner ear hair cells and neurons of the hippocampus. We found that mice lacking the GluRdelta1 protein displayed significant cochlear threshold shifts for frequencies of >16 kHz. These deficits correlated with a substantial loss of type IV spiral ligament fibrocytes and a significant reduction of endolymphatic potential in high-frequency cochlear regions. Vulnerability to acoustic injury was significantly enhanced; however, the efferent innervation of hair cells and the classic efferent inhibition of outer hair cells were unaffected. Hippocampal and vestibular morphology and function were normal. Our findings show that the orphan GluRdelta1 plays an essential role in high-frequency hearing and ionic homeostasis in the basal cochlea, and the locus encoding GluRdelta1 represents a candidate gene for congenital or acquired high-frequency hearing loss in humans.     

Hearing Loss and Hair Cell Death in Mice Given the Cholesterol-Chelating Agent Hydroxypropyl-β-Cyclodextrin

Cyclodextrins are sugar compounds that are increasingly finding medicinal uses due to their ability to complex with hydrophobic molecules. One cyclodextrin in particular, 2-hydroxypropyl-β-cyclodextrin (HPβCD), is used as a carrier to solubilize lipophilic drugs and is itself being considered as a therapeutic agent for treatment of Niemann-Pick Type C disease, due to its ability to mobilize cholesterol. Results from toxicological studies suggest that HPβCD is generally safe, but a recent study has found that it causes hearing loss in cats. Whether the hearing loss occurred via death of cochlear hair cells, rendering it permanent, was unexplored. In the present study, we examined peripheral auditory function and cochlear histology in mice after subcutaneous injection of HPβCD to test for hearing loss and correlate any observed auditory deficits with histological findings. On average, auditory brainstem response thresholds were elevated at 4, 16, and 32 kHz in mice one week after treatment with 8,000 mg/kg. In severely affected mice all outer hair cells were missing in the basal half of the cochlea. In many cases, surviving hair cells in the cochlear apex exhibited abnormal punctate distribution of the motor protein prestin, suggesting long term changes to membrane composition and integrity. Mice given a lower dose of 4,000 mg/kg exhibited hearing loss only after repeated doses, but these threshold shifts were temporary. Therefore, cyclodextrin-induced hearing loss was complex, involving cell death and other more subtle influences on cochlear physiology.     

The lizard ear: Cordylus, Platysaurus and Gerrhosaurus

In further consideration of the lizard ear, the fine structure of the cochlea has been investigated and related to auditory sensitivity in members of the family Cordylidae. The ear of this group of lizards is unusual in that a tectorial membrane is present only in a modified and seemingly vestigial form, and this membrane makes no connections with the auditory hair cells. These cells are provided instead with a series of sallets, small bodies extending in a single row through the dorsal and middle regions of the cochlea, where they rest upon the tips of the ciliary tufts and evidently bring about a stimulation of the hair cells because of their inertia. At the ventral end of the cochlea this line of sallets ends, and here is a single, relatively enormous structure, the culmen papillae, that serves a similar purpose for a large group of hair cells. Consideration is given to the manner of stimulation of the auditory sense cells in these species in relation to others with the usual arrangements involving connections between the ciliary tufts and a tectorial membrane. Included also is a study of a species of Gerrhosaurus, which some have included in the cordylid family and others have placed in a family of its own. The cochlear structure in this species is similar to that of the cordylids in many respects but differs in the ventral region, where instead of the culmen there is a heavy tectorial plate, similarly covering a large number of hair cells but connected to a tectorial membrane. The functioning of these ears is assessed in terms of the cochlear potentials, and is found to vary with species from better than average to excellent in comparison with other lizards investigated. The structural differentiation also is of fairly high degree, and hence it appears that ears without tectorial connections, or with such connections only in a limited region of the cochlea, can perform in a highly serviceable manner.