Involvement of histone H1.2 in apoptosis induced by DNA double-strand breaks

It is poorly understood how apoptotic signals arising from DNA damage are transmitted to mitochondria, which release apoptogenic factors into the cytoplasm that activate downstream destruction programs. Here, we identify histone H1.2 as a cytochrome c-releasing factor that appears in the cytoplasm after exposure to X-ray irradiation. While all nuclear histone H1 forms are released into the cytoplasm in a p53-dependent manner after irradiation, only H1.2, but not other H1 forms, induced cytochrome c release from isolated mitochondria in a Bak-dependent manner. Reducing H1.2 expression enhanced cellular resistance to apoptosis induced by X-ray irradiation or etoposide, but not that induced by other stimuli including TNF-alpha and UV irradiation. H1.2-deficient mice exhibited increased cellular resistance in thymocytes and the small intestine to X-ray-induced apoptosis. These results indicate that histone H1.2 plays an important role in transmitting apoptotic signals from the nucleus to the mitochondria following DNA double-strand breaks.     

Glycosylation of the alpha and beta tubulin by sialyloligosaccharides

To examine whether alpha and beta tubulin are glycoproteins, we used a pyridylamino labeling method and a monoclonal antibody, SG3-1, raised against NeuAcalpha2-3Gal structure. Alpha and beta tubulin from both pig brain and HeLa cells were positive for the SG3-1 antibody by immunoblot assay. Sialidase treatment reduced the reactivity of the SG3-1 antibody to alpha and beta tubulin molecules. N-linked oligosaccharide analysis also showed that alpha and beta tubulin are glycosylated. Moreover, immunofluorescence analysis showed that the filamentous structure recognized by the SG3-1 antibody was overlapped with microtubules, especially in the vicinity of the nucleus. These results indicate that alpha and beta tubulin are glycosylated with sialyloligosaccharides.     

Molecular basis for the treatment of achondroplasia

Achondroplasia (ACH), the most common form of short-limbed dwarfism, and its related disorders are caused by constitutively activated point-mutated fibroblast growth factor receptor 3 (FGFR3). Recent studies have provided a large body of evidence to prove chondrocyte proliferation and differentiation in these disorders. However, little is known about the possible effects of the FGFR3 mutants on apoptosis of chondrocytes. In the present study, we analyzed apoptosis using a chondrogenic cell line, ATDC5, expressing the FGFR3 mutants causing ACH and thanatophoric dysplasia, which is a more severe neonatal lethal form comprising type I and type II. We found that the introduction of these mutated FGFR3s into ATDC5 cells decreased mRNA expression of parathyroid hormone-related peptide (PTHrP) and induced apoptosis. Importantly, replacement of PTHrP prevented the apoptotic changes in ATDC5 cells expressing ACH mutant. Insulin-like growth factor (IGF)-I, which is an important mediator of growth hormone (GH), also reduced apoptosis in ATDC5 cells expressing ACH mutant. IGF-I prevented apoptosis through the phosphatidylinositol 3-kinase and mitogen-activated protein kinase pathways, indicating the mechanisms by which GH treatment improves disturbed bone growth in ACH.     

Laryngeal endocrine cells: topographic distribution and adaptation to chronic hypercapnic hypoxia

The morphology, topographic distribution, effects of denervation, and exposure to hypercapnic hypoxia of endocrine cells were examined in rat larynx. The endocrine cells, which were immunoreactive for protein gene product 9.5 (PGP 9.5) and calcitonin gene-related peptide (CGRP), were observed within the epithelial layer of the laryngeal cavity and in the laryngeal gland, while solitary endocrine cells with apical and/or basal cytoplasmic processes appeared near the glottis. After denervation of the left cervical vagosympathetic trunk and the superior laryngeal nerve, the number of mucosal endocrine cells in the denervated side was not significantly different from that in the intact side. After exposure to hypercapnic hypoxia for 3 months, the number of endocrine cells with PGP 9.5 and CGRP was markedly increased. In conclusion, the secretion of laryngeal endocrine cells may be stimulated by CO2 rather than O2. Furthermore, the endocrine cells and the sensory and autonomic nervous system may regulate each other by an axon reflex mechanism. Endocrine cells appear to play a very important role in the local regulation of the laryngeal mucosa.     

The Mos/MAPK pathway is involved in metaphase II arrest as a cytostatic factor but is neither necessary nor sufficient for initiating oocyte maturation in goldfish

Mos plays a crucial role in meiotic cell division in vertebrates. In Xenopus, Mos is involved in the initiation of oocyte maturation as an initiator and in the arrest at the metaphase II stage (MII) as a component of the cytostatic factor (CSF). The function of Mos is mediated by MAP kinase (MAPK). We investigated the function of the Mos/MAPK pathway during goldfish oocyte maturation induced by 17α,20β-dihydroxy-4-pregnen-3-one (17α,20β-DP), a natural maturation-inducing hormone in fishes. Mos was absent in immature goldfish oocytes. It appeared before the onset of germinal vesicle breakdown (GVBD), increased to a maximum in mature oocytes arrested at MII and disappeared after fertilization. MAPK was activated after Mos synthesis but before maturation-promoting factor (MPF) activation, and its activity reached maximum at MII. Injection of either Xenopus or goldfish c-mos mRNA into one blastomere of 2-cell-stage Xenopus and goldfish embryos induced metaphase arrest, suggesting that goldfish Mos has a CSF activity. Injection of constitutively active Xenopus c-mos mRNA into immature goldfish oocytes induced MAPK activation, but neither MPF activation nor GVBD occurred. Conversely, the injection of goldfish c-mos antisense RNA inhibited both Mos synthesis and MAPK activation in the 17α,20β-DP-treated oocytes, but these oocytes underwent GVBD. These results indicate that the Mos/MAPK pathway is not essential for initiating goldfish oocyte maturation despite its general function as a CSF. We discuss the general role of Mos/MAPK during oocyte maturation, with reference to the difference in contents of inactive MPF (pre-MPF) stored in immature oocytes. Received: 10 February 2000 / Accepted: 25 April 2000     

Process of Egg Formation in the Female Body Cavity and Fertilization in Male Eggs of Phytoseiulus Persimilis (Acari: Phytoseiidae)

The process of egg formation in the body cavity of a phytoseiid mite, Phytoseiulus persimilis, was observed to examine fertilization of male eggs. After insemination, one of the ova at the periphery of the ovary began to expand, taking up yolk. Two pronuclei appeared in the expanded egg, located dorsally in the ovary, and yolk granules were formed gradually. After the egg became filled with yolk granules the two pronuclei fused. The egg moved via the narrow entrance at the ventral region into the oviduct, where the eggshell was formed. When the eggshell was complete, and while embryogenesis proceeded, the egg was deposited. In the meantime some ova began to expand sequentially and two joining pronuclei appeared in expanding eggs. The joining pronuclei in the first egg proved male diploidy. This is additional evidence of pseudo-arrhenotoky in this phytoseiid mite species, since the first eggs developed into males.