Acropetal leaflet initiation of Eschscholzia californica is achieved by constant spacing of leaflets and differential growth of leaf

In compound leaves, leaflet primordia are initiated directionally along the lateral sides. Our understanding of the molecular basis of leaflet initiation has improved, but the regulatory mechanisms underlying spatio-temporal patterns remain unclear. In this study, we investigated the mechanisms of acropetal (from the base to the tip) progression of leaflet initiation in Eschscholzia californica. We established an ultraviolet-laser ablation system to manipulate compound-leaf development. Local ablation at the leaflet incipient site generated leaves with asymmetric morphology. In the majority of cases, leaflets that were initiated on the ablated sides shifted apically. Finite time-course observation revealed that the timing of leaflet initiation was delayed, but the distance from the leaf tip did not decrease. These results were suggestive of the local spacing mechanism in leaflet initiation, whereby the distance from the leaf tip and adjacent pre-existing leaflet determines the position of leaflet initiation. To understand how such a local patterning mechanism generates a global pattern of successive leaflet initiation, we assessed the growth rate gradient along the apical–basal axis. Our time-course analysis revealed differential growth rates along the apical–basal axis of the leaf, which can explain the acropetal progression of leaflet initiation. We propose that a leaflet is initiated at a site where the distances from pre-existing leaflets and the leaf tip are sufficient. Furthermore, the differential growth rate may be a developmental factor underlying the directionality of leaflet initiation.     

Cell Surface Galactosylation Is Essential for Nonsexual Flocculation in Schizosaccharomyces pombe

We have isolated fission yeast mutants that constitutively flocculate upon growth in liquid media. One of these mutants, the gsf1 mutant, was found to cause dominant, nonsexual, and calcium-dependent aggregation of cells into flocs. Its flocculation was inhibited by the addition of galactose but was not affected by the addition of mannose or glucose, unlike Saccharomyces cerevisiae FLO mutants. The gsf1 mutant coflocculated with Schizosaccharomyces pombe wild-type cells, while no coflocculation was found with galactose-deficient (gms1Δ) cells. Moreover, flocculation of the gsf1 mutant was also inhibited by addition of cell wall galactomannan from wild-type cells but not from gms1Δ cells. These results suggested that galactose residues in the cell wall glycoproteins may be receptors of gsf1-mediated flocculation, and therefore cell surface galactosylation is required for nonsexual flocculation in S. pombe.     

Genetic determinants of plasma triglyceride levels in (OLETF x BN) x OLETF backcross rats

Altered lipid metabolism is closely associated with diabetes in humans, although predisposing genetic factors that affect hyperlipidemia have not yet been clarified. Our previously established OLETF strain is an obese rat model of type II diabetes, exhibiting hypertriglycemia as well as hyperinsulinemia, hyperglycemia, insulin resistance, and abundant abdominal fat. To identify genetic factors responsible for dyslipidemic phenotypes in OLETF rats, we performed a whole-genome scan using 293 male (OLETF x BN) x OLETF backcross rats. Our analysis identified two significant quantitative trait loci (QTLs), on rat chromosomes 1 and 8, that are related to fasting triglyceride levels. The chromosome 1 QTL colocalized with Dmo1 (diabetes mellitus, OLETF type 1), a locus previously shown to associate strongly with both fat levels and body weight. The other significant QTL localizes to the chromosome 8 marker D8Mit2, in a region where several apo-lipoprotein genes are clustered.     

Carbendazim-induced abnormal development of the acrosome during early phases of spermiogenesis in the rat testis

Effects of a single, high dose of orally administered carbendazim (100 mg/kg) on acrosome formation in the early phases of spermiogenesis were examined by electron microscopy and immunocytochemistry up to day 7.5 post-treatment. No obvious abnormality of acrosome development was noted in the Golgi phase spermatids on day 1.5 post-treatment. On day 3, step 1 spermatids were seen in stage III seminiferous tubules. In stage V tubules at this post-treatment interval, direct connections between the trans-side saccules of the Golgi stacks and the outer acrosomic membranes were observed in step 5 spermatids. Similar direct connections between these two organelles were also observed in the advanced round spermatids in later stages at days 4.5 and 7.5. On day 4.5, step 1 and 3 spermatids were seen in stage V tubules. On day 7.5, round spermatids with various abnormalities of acrosome development were observed in stage VII tubules, in addition to the discontinuous and granular acrosomes reported previously. These features were not observed in testes of control animals. In the immunocytochemical analysis using an antibody mMN7 that recognizes a protein delivered from the Golgi apparatus to the acrosome, spermatids exposed to carbendazim showed various abnormal immunostaining patterns in the acrosomes. On the other hand, strong immunoreactivity was observed in the Golgi saccules connecting to the acrosomes. These results suggest that in testis treated with carbendazim acrosome development is impaired during the early phases of spermiogenesis, and material supply from the Golgi apparatus to the acrosome is perturbed, which is a possible cause of the abnormal development. Received: 31 March 1998 / Accepted: 28 May 1998     

Genes Involved in Cell Wall Localization and Side Chain Formation of Rhamnose-Glucose Polysaccharide in Streptococcus mutans

We identified in Streptococcus mutans six new genes (rgpA through rgpF), whose disruption results in a loss of serotype-specific antigenicity, specified by the glucose side chains of rhamnose-glucose polysaccharide from the cell wall. Rhamnose and glucose content of the cell wall decreased drastically in all these disruption mutants, except that in the rgpE mutant only the glucose content decreased. RgpC and RgpD are homologous to ATP-binding cassette transporter components and may be involved in polysaccharide export, whereas RgpE may be a transferase of side chain glucose.     

The effect of myosin antibody on the division of starfish blastomeres

Antiserum against starfish egg myosin was produced in rabbits. Antibody specificity to myosin was demonstrated by Ouchterlony's immunodiffusion test and by immunoelectrophoresis in the presence of sodium dodecylsulfate (SDS). The latter technique showed that the antibody binds to both heavy and light chains of egg myosin. Furthermore, the antibody reacted with starfish sperm mysosin and starfish adult muscle myosin at both the heavy and light chains. It did not react with bovine platelet mysosin or rabbit skeletal muscle myosin in Ouchterlony's test; however, a weak reaction was observed in the presence of SDS between the antibody and these myosin heavy chains. Ca- and Mg-ATPase activities of egg myosin were not affected by the antibody, but it did inhibit actin-activated ATPase activity of egg myosin. Microinjection of the antibody into blastomeres of starfish eggs at the two-cell stage was carried out. Anti-egg myosin γ-globulin inhibited the subsequent cleavages at an amount of more than 0.3 ng when injected at interphase. The inhibition was reduced when the injection was carried out near the initiation of cleavage. At the onset of the second cleavage the antibody was not inhibitory; however, an appropriate amount inhibited the third cleavage. Although the disappearance of the nuclear membrane was observed in the presence of the antibody, the formation of the mitotic apparatus was more or less disturbed. However the formation of daughter nuclei seemed to be scarcely affected by the antibody except that the distance between the nuclei was significantly smaller than normal.