A new sensory organ in "primitive" molluscs (Polyplacophora Lepidopleurida), and its context in the nervous system of chitons

Introduction: Chitons (Polyplacophora) are molluscs considered to have a simple nervous system without cephalisation. The position of the class within Mollusca is the topic of extensive debate and neuroanatomical characters can provide new sources of phylogenetic data as well as insights into the fundamental biology of the organisms. We report a new discrete anterior sensory structure in chitons, occurring throughout Lepidopleurida, the order of living chitons that retains plesiomorphic characteristics.

Results: The novel "Schwabe organ" is clearly visible on living animals as a pair of streaks of brown or purplish pigment on the roof of the pallial cavity, lateral to or partly covered by the mouth lappets. We describe the histology and ultrastructure of the anterior nervous system, including the Schwabe organ, in two lepidopleuran chitons using light and electron microscopy. The oesophageal nerve ring is greatly enlarged and displays ganglionic structure, with the neuropil surrounded by neural somata. The Schwabe organ is innervated by the lateral nerve cord, and dense bundles of nerve fibres running through the Schwabe organ epithelium are frequently surrounded by the pigment granules which characterise the organ. Basal cells projecting to the epithelial surface and cells bearing a large number of ciliary structures may be indicative of sensory function. The Schwabe organ is present in all genera within Lepidopleurida (and absent throughout Chitonida) and represents a novel anatomical synapomorphy of the clade.

Conclusions: The Schwabe organ is a pigmented sensory organ, found on the ventral surface of deep-sea and shallow water chitons; although its anatomy is well understood, its function remains unknown. The anterior commissure of the chiton oesophagial nerve ring can be considered a brain. Our thorough review of the chiton central nervous system, and particularly the sensory organs of the pallial cavity, provides a context to interpret neuroanatomical homology and assess this new sense organ.

Retinal Pigment Epithelial Cell DNA is Damaged by Exposure to Benzo[a]pyrene, a Constituent of Cigarette Smoke.

This study examined the effect of exogenous benzo[ a ]pyrene (BaP), an important constituent of cigarette smoke, on cultured bovine retinal pigment epithelial (RPE) cells. Evidence is presented for its metabolic conversion into benzo[ a ]pyrene diol epoxide (BPDE) and the consequent formation of potentially cytotoxic nucleobase adducts in DNA. Cultured RPE cells were treated with BaP at concentrations in the range of 0–100 µm. The presence of BaP was found to cause inhibition of cell growth and replication. BaP induced the expression of a phase I drug metabolizing enzyme which was identified as cytochrome P450 1A1 (CYP 1A1) by RT–PCR and by Western blotting. Coincident with the increased expression of CYP 1A1, covalent adducts between the mutagenic metabolite BPDE and DNA could be detected within RPE cells by immunocytochemical staining. Additional support for their formation was afforded by nuclease P1 enhanced 32P-postlabelling assays on cellular DNA. Single-cell gel electrophoresis (comet) assays showed that exposure of RPE cells to BaP rendered them markedly more susceptible to DNA damage induced by broad band UVB or blue light laser irradiation. In the case of UVB, this is consistent with the photosensitization of DNA cleavage by nucleobase adducts of BPDE. Collectively, these findings imply that BaP has a significant impact on RPE cell pathophysiology and suggest mechanisms whereby exposure to cigarette smoke might cause RPE dysfunction and cell death, thus possibly contributing to degenerative disorders of the retina.

Disruption of the langerin/CD207 Gene Abolishes Birbeck Granules without a Marked Loss of Langerhans Cell Function

Langerin is a C-type lectin expressed by a subset of dendritic leukocytes, the Langerhans cells (LC). Langerin is a cell surface receptor that induces the formation of an LC-specific organelle, the Birbeck granule (BG). We generated a langerin(-/-) mouse on a C57BL/6 background which did not display any macroscopic aberrant development. In the absence of langerin, LC were detected in normal numbers in the epidermis but the cells lacked BG. LC of langerin(-/-) mice did not present other phenotypic alterations compared to wild-type littermates. Functionally, the langerin(-/-) LC were able to capture antigen, to migrate towards skin draining lymph nodes, and to undergo phenotypic maturation. In addition, langerin(-/-) mice were not impaired in their capacity to process native OVA protein for I-A(b)-restricted presentation to CD4(+) T lymphocytes or for H-2K(b)-restricted cross-presentation to CD8(+) T lymphocytes. langerin(-/-) mice inoculated with mannosylated or skin-tropic microorganisms did not display an altered pathogen susceptibility. Finally, chemical mutagenesis resulted in a similar rate of skin tumor development in langerin(-/-) and wild-type mice. Overall, our data indicate that langerin and BG are dispensable for a number of LC functions. The langerin(-/-) C57BL/6 mouse should be a valuable model for further functional exploration of langerin and the role of BG.

Characterization of a spontaneous mouse retinal pigment epithelial cell line B6-RPE07.

PURPOSE. A spontaneously arising retinal pigment epithelial (RPE) cell line (B6-RPE07) was cloned from a primary culture of mouse RPE cells and maintained in culture for more than 18 months. Morphologic and functional properties of this cell line have been characterized.

METHODS. The morphology of the B6-RPE07 cells was examined by phase-contrast light microscopy, electron microscopy, and confocal microscopy. Barrier properties were measured by the flux of fluorescence from the apical to the basolateral compartment of culture chambers. The abilities of the cells to bind/phagocytose photoreceptor outer segments (POS) were determined by confocal microscopy, electron microscopy, and flow cytometry. Cytokine/chemokine secretion was measured by cytometric bead array. The expression of visual cycle proteins was determined by RT-PCR and Western blotting.

RESULTS. In standard culture conditions, B6-RPE07 cells display cobblestone morphology. When cultured on three-dimensional (3D) collagen gel–coated membranes, B6-RPE07 cells exhibit a monolayer epithelial polarization with apical surface microvilli. Immunohistochemistry of B6-RPE07 cultures revealed a high expression of pan-cytokeratin. B6-RPE07 cells also expressed the retinal pigment epithelium-specific marker CRALBP, but not RPE65. Cell junction proteins ZO-1 and ß-catenin, but not claudin-1/3 or occludin-1, were observed in B6-RPE07 cells. B6-RPE07 cells are able to bind, phagocytose, and digest POS. Finally, B6-RPE07 cells produce high levels of IL-6 and CCL2.

CONCLUSIONS. This is the first report of a mouse RPE cell line with morphology, phenotype, and function similar to those of in vivo mouse RPE cells. This cell line will be a valuable resource for future RPE studies, in particular for in vivo gene modification and transplantation studies.

Age-dependent accumulation of lipofuscin in perivascular and subretinal microglia in experimental mice

Fundus autofluorescence (AF) imaging by confocal scanning laser ophthalmoscopy has been widely used by ophthalmologists in the diagnosis/monitoring of various retinal disorders. It is believed that fundus AF is derived from lipofuscin in retinal pigment epithelial (RPE) cells; however, direct clinicopathological correlation has not been possible in humans. We examined fundus AF by confocal scanning laser ophthalmoscopy and confocal microscopy in normal C57BL/6 mice of different ages. Increasingly strong AF signals were observed with age in the neuroretina and subretinal/RPE layer by confocal scanning laser ophthalmoscopy. Unlike fundus AF detected in normal human subjects, mouse fundus AF appeared as discrete foci distributed throughout the retina. Most of the AF signals in the neuroretina were distributed around retinal vessels. Confocal microscopy of retinal and choroid/RPE flat mounts demonstrated that most of the AF signals were derived from Iba-1+ perivascular and subretinal microglia. An age-dependent accumulation of Iba-1+ microglia at the subretinal space was observed. Lipofuscin granules were detected in large numbers in subretinal microglia by electron microscopy. The number of AF+ microglia and the amount of AF granules/cell increased with age. AF granules/lipofuscin were also observed in RPE cells in mice older than 12 months, but the number of AF+ RPE cells was very low (1.48 mm-2 and 5.02 mm-2 for 12 and 24 months, respectively) compared to the number of AF+ microglial cells (20.63 mm-2 and 76.36 mm-2 for 6 and 24 months, respectively). The fluorescence emission fingerprints of AF granules in subretinal microglia were the same as those in RPE cells. Our observation suggests that perivascular and subretinal microglia are the main cells producing lipofuscin in normal aged mouse retina and are responsible for in vivo fundus AF. Microglia may play an important role in retinal aging and age-related retinal diseases.

Apolipoprotein E genotype is associated with macular pigment optical density.

PURPOSE: Age-related macular degeneration (AMD) is the most common cause of blindness in older people in developed countries, and risk factors for this condition may be classified as genetic and environmental. Apolipoprotein E is putatively involved in the transport of the macular pigment (MP) carotenoids lutein (L) and zeaxanthin (Z) in serum and may also influence retinal capture of these compounds. This study was designed to investigate the relationship between macular pigment optical density (MPOD) and ApoE genotype. METHODS: This was a cross-sectional study of 302 healthy adult subjects. Dietary intake of L and Z was assessed by food frequency questionnaire, and MPOD was measured by customized heterochromatic flicker photometry. Serum L and Z were measured by HPLC. ApoE genotyping was performed by direct polymerase chain reaction amplification and DNA nucleotide sequencing from peripheral blood. RESULTS: Genotype data were available on 300 of the 302 (99.3%) subjects. The mean (+/- SD) age of the subjects in this study was 47.89 +/- 11.05 (range, 21-66) years. Subjects were classed into one of three ApoE genotype groups, as follows: group 1, epsilon2epsilon2 or epsilon2epsilon3; group 2, epsilon3epsilon3; group 3, epsilon2epsilon4 or epsilon3epsilon4 or epsilon4epsilon4. All three groups were statistically comparable in terms of age, sex, body mass index, cigarette smoking, and dietary and serum levels of L and Z. There was a statistically significant association between ApoE genotype and MPOD. Subjects who had at least one epsilon4 allele had a higher MPOD across the macula than subjects without this allele (group 1 MPOD area, 0.70 +/- 0.40; group 2 MPOD area, 0.67 +/- 0.42; group 3 MPOD area, 0.85 +/- 0.46; one-way ANOVA, P = 0.014. CONCLUSIONS: These results suggest that ApoE genotype status is associated with MPOD. This association may explain, at least in part, the putative protective effect of the epsilon4 allele for AMD and is consistent with the view that apolipoprotein profile influences the transport and/or retinal capture of circulating L and/or Z.