Most models of hereditary hypotrichosis are due to alterations in growth factors and transcription factors, and the examples of causative mutations in hair keratin genes are limited. The Hirosaki hairless rat (HHR) is a mutant strain spontaneously derived from Sprague-Dawley rats (SDRs). In this study, the locus of the responsible gene was examined by linkage analysis and mapped on chromosome 7q36. Because many basic keratin genes are clustered on 7q36, their expression was examined. Reverse transcription-PCR and genomic PCR indicated that the Kb21 (Krt81), -23 (Krt83), and -26 (Krt86) genes encoding basic hair keratins were not expressed and were deleted. Furthermore, 80-kb genomic DNA ranging from exon 9 of Kb25 (Krt85) to exon 9 of Krt2-25 was deleted. The breakpoints of these genes were within a 95-bp portion shared by the two genes, suggesting that deletion due to non-allelic homologous recombination occurred. Proteins identified as Kb21, Kb23, and Krt2-25 in SDR hairs by mass spectrometry were not detected in HHR. Instead, the product of a fusion gene became dominant in HHR. Because fusion occurred between the exons of the two genes with the same sequences, the product was identical to the wildtype Kb25 protein. By using immunohistochemistry, Kb21 was not detected in HHR hair follicles. Kb25 was expressed in the cortex in HHRs, whereas it was in the medulla in SDRs. This study clearly illustrates the importance of hair keratin genes in hair growth.The large keratin multigene family comprises cytokeratins, which are differentially expressed in the various types of epithelia, and hair keratins, expressed in hard keratinized structures such as hairs, nails, and claws. These keratins can be divided into the acidic type I and the basic-to-neutral type II members, which form the 10 nm intermediate filament network through the obligatory association of equimolar amounts of type I and type II keratins (1). Previous studies on the hair keratins of several mammals reveal the presence of nine type I and six type II members (1, 2). Hair keratins are collectively designated "H" for hair, "b" for the basic members (Hb), and "a" for the acidic members (Ha) (3). In the case of rats, genes encoding the basic members are designated Kb21-26. In rats, the type I keratin genes are clustered on chromosome 10q31 and the type II gene cluster on 7q36 (4). The latter cluster includes Kb21-26 on a DNA domain of ϳ200 kb.Hairs are produced in hair follicles. The hair follicle includes not only the cortex and medulla but also the inner root sheath, companion layer, and outer root sheath (5). Recent studies have revealed that some specific cytokeratins are expressed in the inner root sheath (6) and other components (4, 7). Numerous growth factors and cytokines such as Wnt (8, 9) and transforming growth factor (10, 11) are involved in hair follicle formation, and mutations of these genes cause various types of hypotrichosis. Furthermore, loss-of-function mutation of the transcription factor Foxn1 is responsible for the nude phenotype (12...

To clarify the role of zinc in the mechanism of salivary secretion, the effects of zinc deficiency on the morphologic findings and secretory function of the salivary gland were investigated with a rat model of chronic zinc deficiency, prepared by feeding a zinc-deficient diet, and a rat model of acute zinc deficiency, prepared by administration of a zinc chelator, dithizone. In rats with chronic zinc deficiency, the granule production in the granular duct cells was decreased, but the glandular epithelial cells and myoepithelial cells showed no degenerative or other destructive morphologic changes. The degranulation of the granular duct cells and acinar cells in response to acetylcholine hydrochloride seen in control rats was strongly inhibited in rats with acute and chronic zinc deficiency. The contractile response of the actin microfilament bundles in the myoepithelial cells to acetylcholine seen in the control rats was also absent in the zinc-deficient rats. Further, electron microscopy of the submandibular gland stained by Timm's method disclosed prominent zinc localization at the membrane surface, granules, and vesicles of the glandular epithelial cells and in the pits of the myoepithelial cells. These findings suggest that zinc, together with many zinc-dependent enzymes, is closely involved in the production and degranulation of secretory granules in the glandular epithelial cells, and also in the contraction of the myoepithelial cells in the submandibular gland.

Although peroxisomal bifunctional enzyme (enoyl-CoA hydratase/ L-3-hydroxyacyl-CoA dehydrogenase; BE) is a positive marker for peroxisome proliferation, it is completely absent or expressed very weakly in rat hepatic preneoplastic and neoplastic lesions induced by peroxisome proliferators (PP). After administration of PP for 8-15 weeks, some rats exhibit BE-negative preneoplastic foci but other rats do not. In the present study, to investigate the involvement of glutathione S-transferase (GST) M1 gene polymorphism in interindividual differences in susceptibility to PP, we developed a method to determine the genotypes of rats. We then examined whether rats with one type encoding 198 Asn-199 Cys (NC-type) or another encoding 198 Lys-199 Ser (KS-type) exhibit differences in clofibrate (CF) susceptibility. After administration of 0.3% CF for 6 weeks or more, BE-negative foci were found immunohistochemically in KS/KS-type rats, but not in NC/NC-type rats. The number of BE-negative foci in KS/KS rats was 15.3 ± ± ± ± 9.0 foci/cm 2 of liver section after 6 weeks of CF administration, and the values did not alter thereafter. The mean areas of BEnegative foci in KS/KS rat livers increased during the period from 6 to 60 weeks. At weeks 30 and 60, almost all BE-negative foci exhibited a clear cell phenotype, a type of preneoplastic hepatic lesion. BE-negative foci were devoid of peroxisome proliferatoractivated receptor α α α α, whereas surrounding tissues were positive for the receptor. These results indicate that rats that are polymorphic for the GST M1 gene exhibit different susceptibilities to CF in vivo. (Cancer Sci 2006; 97: 703-709) P eroxisome proliferators, including CF, induce hepatomegaly, proliferation of peroxisomes and expression of several peroxisomal enzymes in rodent livers, such as acyl-CoA oxidase, BE and 3-ketoacyl-CoA thiolase, which participate in β-oxidation of fatty acids and result in the production of hydrogen peroxide. (1)(2)(3)(4)(5) Induction of BE expression in rat liver by PP is mediated by PPARα, which forms a complex with RXR. The PPARα-RXR complex binds to PP-responsive elements present in the 5′-flanking region of the BE gene and other target genes. (6) Prolonged administration of PP to rats is associated with the development of hepatic preneoplastic and neoplastic lesions. (7)(8)(9)(10)(11) These lesions do not express GST-P, a reliable marker for preneoplastic lesions in rats induced by the great majority of carcinogens. (12,13) Using a rat liver bioassay system with GST-P as a marker, the carcinogenic potential of most chemicals, including mutagenic carcinogens, can be evaluated within 8 weeks. (13,14) As PP do not cause mutagenic effects in shortterm in vitro assays, (15,16) administration of PP to rats for 60-100 weeks is required to evaluate their carcinogenic potential. PP include a broad spectrum of compounds of industrial, pharmaceutical and agricultural importance, such as phthalate ester plasticizers, lipid-lowering drugs and herbicides. (17) Thus, methods for early detection o...

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Lead nitrate induces hepatocyte proliferation and subsequent apoptosis in rat livers. Iron is a constituent of heme and is also required for cell proliferation. In this study, the expression of ferritin light-chain (FTL), the major iron storage protein, was investigated in rat livers after a single intravenous injection of lead nitrate. Western blotting and immunohistochemistry revealed that FTL was increased in hepatocytes around the central veins and strongly expressed in nonparenchymal cells. Some FTL-positive nonparenchymal cells were identified as Kupffer cells that were positive for CD68. FTL-positive Kupffer cells occupied about 60% of CD68-positive cells in the periportal and perivenous areas. The relationships between FTL expression and apoptosis induction or the engulfment of apoptotic cells were examined. TUNEL-positive cells were increased in the treatment group, and enhanced expression of milk fat globule EGF-like 8 was demonstrated in some Kupffer cells and hepatocytes, indicating enhanced apoptosis induction and phagocytosis of apoptotic cells. FTL-positive Kupffer cells were not detected without lead nitrate treatment or in rat livers treated with clofibrate, which induces hepatocyte proliferation but not apoptosis. These results suggest that FTL expression in Kupffer cells after lead treatment is dependent on phagocytosis of apoptotic cells.