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.

Dynamic expression pattern of Ca(2+)/calmodulin-dependent protein kinase II gene in the central nervous system of Drosophila throughout development

Calcium/calmodulin-dependent protein kinase II (CaM KII) is thought to be involved in the majority of the neuronal functions mediated by intracellular free Ca(2+), and has been implicated in long-term potentiation, learning, and memory. In this work, we have examined in detail the RNA expression pattern for the Drosophila CaM KII gene by in situ hybridization, during embryonic, larval, pupal, and adult stages. Our results indicate that expression of CaM KII was homogeneous in early embryos, but that during development the gene transcription rapidly became restricted to neuroblasts and their progeny in the nervous system. This predominant expression in the nervous system is maintained during late embryogenesis and post-embryonic development. A signal compartmentalization appeared in the larval central nervous system, where the CaM KII expression became progressively concentrated in the anterior ganglia. In the adult brain, a specific expression was more abundant in a subset of neurons around the central brain, particularly the mushroom bodies and the central complex, structures that play an important role in learning and memory.

Analysis of period circadian expression in the Drosophila head by in situ hybridization

The expression of the period (per) gene of Drosophila melanogaster has been studied by in situ hybridization in the adult's head, where it is required for the fly to exhibit behavioral circadian rhythms. We have used non-radioactive in situ hybridization to obtain a high sensitivity and specificity on head sections, with single cell resolution. Consistent with previous per protein- or per reporter gene-expression, per-expressing cells were detected in the optic lobes and the central brain, as well as in the head sensory organs: eyes, ocelli, maxillary palps and proboscis. In the brain and the eyes, circadian fluctuations of the per mRNA abundance were observed in different per expressing cells.

Genetical analysis of visual system disorganizer (vid), a new gene involved in normal development of eye and optic lobe of the brain in Drosophila melanogaster

A neuroanatomical screening of a collection of P-element mutagenized flies has been carried out with the aim of finding new mutants affecting the optic lobe of the adult brain in Drosophila melanogaster. We have identified a new gene that is involved in the development of the adult axon array in the optic ganglia and in the ommatidia assembly. We have named this locus visual system disorganizer (vid). Reversional mutagenesis demonstrated that the vid mutant was the result of a P-element insertion in the Drosophila genome and allowed us to generate independent alleles, some of which resulted in semilethality, like the vid original mutant, while the others were completely lethal. A genetic somatic mosaic analysis indicated that the vid gene is required in the eye for its normal development by inductive effects. This analysis also suggests an inductive effect of the vid gene on the distal portion of the optic lobe, particularly the lamina and the first optic chiasma. Moreover, the absence of mutant phenotype in the proximal region of the optic ganglia, including the medulla, the second optic chiasma, and the lobula complex underlying mosaic eyes, is suggestive of an autonomously acting mechanism of the vid gene in the optic lobe. The complete or partial lethality generated by different mutations at the vid locus suggests that this gene's role may not be limited to the visual system, but may also affect a vital function during Drosophila development.

Diffuse cutaneous infection caused by a presumed monoxenous trypanosomatid in a patient infected with HIV

A patient infected with human immunodeficiency virus developed a diffuse cutaneous nodular syndrome. The parasite isolated from a skin nodule was studied by isoenzymatic characterization and transmission electron microscopy of both culture forms and those in the patient's skin biopsy. The parasite's ultrastructure was that of a typical member of the family Trypanosomatidae, but it differed isoenzymatically from all 'new and 'old World' species of Leishmania, Trypanosoma and Sauroleishmania. We believe that it was a (presumably) monoxenous 'lower trypanosomatid.

Differential cellular expression of cystic fibrosis transmembrane regulator in human reproductive tissues. Clues for the infertility in patients with cystic fibrosis

Cystic fibrosis (CF) is characterized by a wide spectrum of clinical manifestations, including reproductive problems. Practically all males affected by the disease are infertile due to azoospermia associated with pathology of the male ducts, whereas females with CF have reduced fertility. To study the mechanism of reproductive pathology in CF patients, we analyzed the levels and localization of expression of the cystic fibrosis transmembrane regulator (CFTR) gene in relevant postnatal tissues. Significant expression was detected in the epithelium of the epididymis and vas deferens. Minimal expression, not associated with specific cell types, was seen in the mature testis. In female genitalia, variable levels of expression were seen in the cervical epithelium and fallopian tube. The endometrial epithelium and glands expressed CFTR at high levels only after puberty. No expression was seen in ovaries. Deficient secretory function of CFTR in males but not in females may lead to organ damage probably as a consequence of excessive concentration of viscid luminal contents.

Leishmania amazonensis: acidic organelles in amastigotes

Leishmania amastigotes are intracellular protozoan parasites which exclusively invade cells of the macrophage series and multiply within phagolysosomes. Recent studies showed that intracellular and isolated amastigotes of L. amazonesis are killed by amino acid esters which appear to be trapped within as yet unidentified, possibly acidified, "lysosome-like" parasite compartments and cleaved by hydrolytic enzyme(s) (M. Rabinovitch, V. Zilberfarb, and C. Ramazeilles, 1986, Journal of Experimental Medicine 163, 520-535). In the present study, we have localized acidic compartments of Leishmania amastigotes using as a probe the weak base 3-(2,4 dinitroanilino)-3'-amino-N-methyldipropylamine (DAMP). This indicator, which can be detected within cells by light and electron microscopy using immunocytochemical immunocytochemical methods, mainly accumulates within megasomes and in dense inclusion vacuoles. With the help of quantitative assays to titrate cell-associated DAMP, it was found that (a) its uptake is temperature dependent and thus probably requires an energy supply, (b) the proton ionophore monensin partially inhibits the trapping of DAMP, and (c) monensin greatly increases its efflux from cells. These results, as well as those obtained by quantitative ultrastructural immunocytochemistry of cells incubated with DAMP in the absence or presence of monensin, show that megasomes and inclusion vacuoles have a low pH probably maintained by an active process. Furthermore, confirming the report of H. F. Hassan and G. H. Coombs (1987, Molecular and Biochemical Parasitology 23, 285-296) megasomes were found to display acid phosphatase activity at both light and electron microscope levels. This, together with the demonstration that megasomes are acidified, suggests that these organelles may be targets for amino acid derivatives.

Immunolabelling of bacteriophage lambda receptor protein (LamB) on thin sections of E. coli embedded in Lowicryl

LamB is one of the major cellular proteins when E. coli is grown in the presence of maltose and is localized in the outer membrane. Previous immunolabellings obtained with monoclonal antibodies showed that this protein is a transmembrane protein and led to the detection of 4 epitopes exposed on the cell surface and 2 located on the inner surface of the outer membrane (Scheckman et al., 1983). In the present study, we have used this biological model in order to see whether these two classes of epitopes could be distinguished by immunocytochemical labelling performed on thin sections of E. coli embedded in Lowicryl K4M (Carleman et al., 1982). The optimal conditions of fixation and embedding were first established for labelling with poly- or monoclonal antibodies detected by Protein A-gold complexes. The analysis of gold particle distribution on each side of the outer membrane after labelling with a polyclonal serum or after its adsorption on intact bacteria allowed us to conclude that the resolution of immunolabelling on thin sections was about 20 nm. The use monoclonal antibodies met with difficulties due mostly to the nonspecific labelling of the cytoplasm. Although this nonospecific labelling was decreased by fixing bacteria with paraformaldehyde alone, only one antibody gave a correct specific labelling after high dilution (1/3000). The gold particle distribution obtained with this antibody confirmed the location on the cell surface of this epitope.

Cytochemical study of the nucleolus of the slime mold Dictyostelium discoideum

The nucleus of the slime mold Dictyostelium discoideum is characterized by the presence of several large dense masses which are all in tight contact with the nuclear membrane. These dense masses, considered as nucleoli, present a rather homogeneous texture, in which dense chromatin, fibrillar, and granular material are not easily detected. The autoradiographic study of [3H]uridine pulse-labeled cells showed that the majority of the silver grains were located inside these masses. The use of EDTA regressive-staining, acetylation and enzymatic digestion indicated that they are mostly composed of RNP and are totally devoid of dense chromatin as the rest of the nucleus is. After treatment with actinomycin D, fibrillar and granular material segregated but no chromatin could be found. All these observations confirmed that the dense masses correspond to nucleoli despite their peculiar ultrastructure. It can also be concluded that this type of nucleoli cannot be considered as a taxonomic character of the slime molds because it does not exist in all slime molds and was observed in some dinoflagellates, and ascomycetes.

Isolation of malaria merozoites: release of Plasmodium chabaudi merozoites from schizonts bound to immobilized concanavalin A

The ability of concanavalin A to bind erythrocytes but not malarial parasites was used for the development of a method of merozoite isolation: cells from infected blood were allowed to bind to a column of concanavalin A linked to Sepharose beads and merozoites naturally released by maturation of the schizonts bound to the gel were collected. The principle of this method allows its application to several Plasmodium species. The kinetics of merozoite production and the quality of the preparations (purity, infectivity, and ultrastructural morphology) were investigated by using Plasmodium chabaudi.