Expression and function of a limb‐patterning gene Distal‐less in the soldier‐specific morphogenesis in the nasute termite Nasutitermes takasagoensis

One of the major foci in evolutionary developmental biology is to understand developmental mechanisms that underlie the acquisition of morphological novelties. Termite soldiers, the highly specialized defensive caste, show exaggerated species‐specific morphologies, mostly enlarged mandibles. Soldiers of the subfamily Nasutitermitinae (Termitidae), however, possess a novel structure for defense in their heads, that is a horn‐like frontal projection (nasus) from which defensive chemicals are discharged. Just prior to the molt into presoldiers (the preceding stage to soldiers) from workers, a nasus disc, or a nasus primordium, is observed under the worker head cuticle. In order to understand the developmental underpinnings of this evolutionarily novel structure, the role of a homeobox gene Distal‐less (Dll) during nasus development was examined in this study, using a nasute termite Nasutitermes takasagoensis. Histological observations showed that complex developmental processes comprising epidermal evagination and invagination through changes in cell shape and cell proliferation formed the projection and the gland. Immunohistochemistry showed that Dll was localized in the developing nasus disc, but not in the frontal‐gland primordium. Consistent with this finding, Dll RNA interference only repressed nasus growth not the frontal‐gland formation. Taken together, the co‐option of Dll is suggested to contribute to the acquisition of a novel defensive structure in a termite lineage, coupled with the acquisition of adaptive defensive behaviors.     

Insulin-like growth factor-I stimulates cell proliferation in the outer layer of Hertwig’s epithelial root sheath and elongation of the tooth root in mouse molars in vitro

To elucidate the mechanism of root formation in tooth development, we examined the role of insulin-like growth factor I (IGF-I) on early root formation in mandibular first molar teeth from 5-day-old mice. Immunohistochemistry revealed the specific localization of the IGF-I receptor in Hertwigs epithelial root sheath (HERS) in the tooth root. The effect of IGF-I on root development, especially on HERS, was subsequently examined in vitro. The control culture showed normal development of HERS and the periodontium, resembling that in vivo. However, the presence of 100 ng/ml IGF-I resulted in elongation of HERS and increased cell proliferation in its outer layer. These effects were negated by the addition of antibodies specific for IGF-I. Thus, we propose that IGF-I is involved in early root formation by regulating the mitotic activity in the outer layer of HERS.This study was partly supported by grants to N.F. from KAKENHI (no. 13671909), to N.F. and M.J.T. from the Promotion of 2001-Multidisciplinary Research Projects in 2001–2005, and to N.F. and K.I. from Iwate Medical University—Keiryokai Research Foundation (no. 64).     

Multiple quantitative trait loci modify cochlear hair cell degeneration in the Beethoven (Tmc1Bth) mouse model of progressive hearing loss DFNA36

Dominant mutations of transmembrane channel-like gene 1 (TMC1) cause progressive sensorineural hearing loss in humans and Beethoven (Tmc1Bth/+) mice. Here we show that Tmc1Bth/+ mice on a C3HeB/FeJ strain background have selective degeneration of inner hair cells while outer hair cells remain structurally and functionally intact. Inner hair cells primarily function as afferent sensory cells, whereas outer hair cells are electromotile amplifiers of auditory stimuli that can be functionally assessed by distortion product otoacoustic emission (DPOAE) analysis. When C3H-Tmc1Bth/Bth is crossed with either C57BL/6J or DBA/2J wild-type mice, F1 hybrid Tmc1Bth/+ progeny have increased hearing loss associated with increased degeneration of outer hair cells and diminution of DPOAE amplitudes but no difference in degeneration of inner hair cells. We mapped at least one quantitative trait locus (QTL), Tmc1m1, for DPOAE amplitude on chromosome 2 in [(C/B)F1xC]N2-Tmc1Bth/+ backcross progeny, and three other QTL on chromosomes 11 (Tmc1m2), 12 (Tmc1m3), and 5 (Tmc1m4) in [(C/D)F1xC]N2-Tmc1Bth/+ progeny. The polygenic basis of outer hair cell degeneration in Beethoven mice provides a model system for the dissection of common, complex hearing loss phenotypes, such as presbycusis, that involve outer hair cell degeneration in humans.     

Identification and characterisation of structural maintenance of chromosome 1 (smc1) mutants of Coprinopsis cinerea

A Coprinopsis cinerea homokaryotic fruiting strain was mutagenised, identifying a mutant that exhibited a hyphal growth temperature sensitive defect and hyphal knot development defect at an early fruiting stage, even at the hyphal growth permissive temperature. Microscopic observation suggested that the mutant nuclei exhibited defects in the metaphase to anaphase transition at the restrictive temperature. The gene in which the mutation occurred was cloned, sequenced and determined to be homologous to smc1. Sequence analyses of the mutant revealed deletion of 28 base pairs in the 19th intron of the Cc.smc1 gene, resulting in complete failure of splicing of that intron and in insertion of 14 amino acids in the C-terminal region of the Cc.Smc1 protein. We isolated eight hyphal growth revertants and identified four intragenic suppressors. All were the result of amino acid substitutions in the C-terminal region. Three of the suppressors caused reversion of the arrest in an early fruiting stage. One of the suppressors exhibited cold sensitivity and failed to suppress the fruiting defect, suggesting that flexibility of a lobe in the C-terminal region is important for proper function of Cc.Smc1.     

Dual subcellular localization in the endoplasmic reticulum and peroxisomes and a vital role in protecting against oxidative stress of fatty aldehyde dehydrogenase are achieved by alternative splicing

Fatty aldehyde dehydrogenase (FALDH, ALDH3A2) is thought to be involved in the degradation of phytanic acid, a saturated branched chain fatty acid derived from chlorophyll. However, the identity, subcellular distribution, and physiological roles of FALDH are unclear because several variants produced by alternative splicing are present in varying amounts at different subcellular locations. Subcellular fractionation experiments do not provide a clear-cut conclusion because of the incomplete separation of organelles. We established human cell lines heterologously expressing mouse FALDH from each cDNA without tagging under the control of an inducible promoter and detected the variant FALDH proteins using a mouse FALDH-specific antibody. One variant, FALDH-V, was exclusively detected in peroxisomal membranes. Human FALDH-V with an amino-terminal Myc sequence also localized to peroxisomes. The most dominant form, FALDH-N, and other variants examined, however, were distributed in the endoplasmic reticulum. A gas chromatography-mass spectrometry-based analysis of metabolites in FALDH-expressing cells incubated with phytol or phytanic acid showed that FALDH-V, not FALDH-N, is the key aldehyde dehydrogenase in the degradation pathway and that it protects peroxisomes from oxidative stress. In contrast, both FALDHs had a protective effect against oxidative stress induced by a model aldehyde for lipid peroxidation, dodecanal. These results suggest that FALDH variants are produced by alternative splicing and share an important role in protecting against oxidative stress in an organelle-specific manner.