Junko Kuno

Negative Regulation of BMP/Smad Signaling by Tob in Osteoblasts

Bone morphogenetic protein (BMP) controls osteoblast proliferation and differentiation through Smad proteins. Here we show that Tob, a member of the emerging family of antiproliferative proteins, is a negative regulator of BMP/Smad signaling in osteoblasts. Mice carrying a targeted deletion of the tob gene have a greater bone mass resulting from increased numbers of osteoblasts. Orthotopic bone formation in response to BMP2 is elevated in tob-deficient mice. Overproduction of Tob represses BMP2-induced, Smad-mediated transcriptional activation. Finally, Tob associates with receptor-regulated Smads (Smad1, 5, and 8) and colocalizes with these Smads in the nuclear bodies upon BMP2 stimulation. The results indicate that Tob negatively regulates osteoblast proliferation and differentiation by suppressing the activity of the receptor-regulated Smad proteins.

Unrestrained nociceptive response and disregulation of hearing ability in mice lacking the nociceptin/orphaninFQ receptor.

In the G‐protein‐coupled receptor superfamily, the opioid receptor subfamily is constituted of the three distinct opioid receptors (namely δ‐, μ‐ and κ‐subtypes) and the receptor for nociceptin (also designated orphaninFQ). The members of the opioid receptor subfamily were known to mediate a variety of cellular inhibitory effects. The three opioid receptors are known to play central roles in mediating analgesia and many other physiological activities; however, the nociceptin receptor was identified recently and less is known about its physiological roles. Here we report the generation and characterization of mice lacking the nociceptin receptor. The knockout mice showed no significant differences in nociceptive threshold and locomotor activity compared with control mice, but they lost nociceptin‐induced behavioral responses. These results indicate that the nociceptin system is not essential for regulation of nociception or locomotor activity. On the other hand, we found insufficient recovery of hearing ability from the adaptation to sound exposure in the mutant mice. Thus, the nociceptin system appears to participate in the regulation of the auditory system.

Generation and Characterization of Mutant Mice Lacking Ryanodine Receptor Type 3

The ryanodine receptor type 3 (RyR-3) functions as a Ca2+-induced Ca2+ release (CICR) channel and is distributed in a wide variety of cell types including skeletal muscle and smooth muscle cells, neurons, and certain non-excitable cells. However, the physiological roles of RyR-3 are totally unclear. To gain an insight into the function of RyR-3 in vivo, we have generated mice lacking RyR-3 by means of the gene targeting technique. The mutant mice thus obtained showed apparently normal growth and reproduction. Although Ca2+-induced Ca2+ release from intracellular Ca2+ stores of the mutant skeletal muscle differed in Ca2+ sensitivity from that of wild-type muscle, excitation-contraction coupling of the mutant muscle seemed to be normal. Moreover, we could not find any significant disturbance in the smooth muscle and lymphocytes from the mutant mice. On the other hand, the mutant mice showed increased locomotor activity, which was about 2-fold greater than that of the control mice. These results indicate that the loss of RyR-3 causes no gross abnormalities and suggest that the lack of RyR-3-mediated Ca2+ signaling results in abnormalities of certain neurons in the central nervous system.

1006 Mouse Zic1 has an essential tole in cerebellar development

Jun Aruga’, Osamu Minowa 2, Junko Kuno”, Hiroyuki Yaginuma3, Takeharu Naga?, Tetsuo Noda2, Katsuhiko Mikoshiba’ Zic genes were found as a gene family encoding zinc finger proteins expressed restrictedly in the adult mouse cerebellum. We recently showed that the genes are the vertebrate homologues of Drosophila odd-paired, which may play essential roles in parasegmental subdivision and in visceral mesoderm development. To clarify the role of Zic genes in the cerebellar development, we targeted Zicl gene, which is a major species in the adult CNS among the Zic family. Homozygous mutants showed remarkable ataxia during their postnatal life and most of them died within a month after birth. Morphologically, the cerebellum was hypoplastic and showed abnormal foliation pattern. The abnormality of cerebellar foliation could be detected as early as 17 days post coitum. These findings suggested that Zicl has an essential role in the vertebrate development. Further characterization on the family may reveal genetic interactions with other genes involved in cerebellar development.