Ascendente Handschwingen-Mauser beiMuscicapa striata

Zusammenfassung Ascendente Mauser der Handschwingen beiMuscicapa striata wird beschrieben. Der Ersatz der Handschwingen von der äußeren zur inneren fortschreitend ist einzigartig bei den Passeres. Bisher war von allen untersuchten Passeres nur die descendente, von innen nach außen fortschreitende Mauser der Handschwingen bekannt. Auch die nächstverwandten ArtenMuscicapa gambagae, M. sibirica undM. latirostris mausern descendent. Vermutlich verlaufen auch die Mauser der Armschwingen und der Schwanzfedern beiM. striata nach einem anderen Schema als bei den übrigen Passeres. Die mögliche Bedeutung der Erscheinung wird diskutiert.

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Summary The examination of eight specimens of the palearctic FlycatcherMuscicapa striata collected in the wintering grounds in Tanganyika Territory and Kenya Colony, all in different stages of complete prenuptial moult, yielded the unexpected result of ascending primary moult (beginning with the outermost primary), in contrast to the descending mode so far known to be followed by all Passeriformes.With regard to the moult of secondaries and tail-feathers the material, somewhat scanty in this respect, seems to show that in both these feather-tracts too the ordinary Passerine sequence is reversed, the rectrices being moulted centripetally and the secondaries diverging from a single moult centre represented by the sixth, but this needs corroboration.A superficial search among other members of the genusMuscicapa, includingM. gambagae, and among other genera of Flycatchers disclosed the usual descending primary moult in all these forms (listed in the text).A possible functional meaning of the ascending primary moult inMuscicapa striata is discussed.

     

Microtubule assembly is required for the formation of the pronuclei,nuclear lamin acquisition,and DNA synthesis during mouse,but not sea urchin,fertillization

Microtubule assembly is required for the formation of the male and female pronuclei during mouse, but not sea urchin, fertilization. In mouse oocytes, 50 μM colcemid prevents the decondensation of the maternal meiotic chromosomes and of the incorporated sperm nucleus during in vitro fertilization. Nuclear lamins do not associate with either of the parental chromatin sets although peripherin, the PI nuclear peripheral antigen, appears on both. DN A synthesis docs not occur in these fertilized, colcemid-arrested oocytes. This effect is limited to the first hours after ovulation, since colcemid added 4–6 hours later no longer prevents pronuclear development, lamin acquisition, or DNA synthesis. Neither microtubule stabilization with 10 μM taxol nor microfilament inhibition with 10 μM cytochalasin D or 2.2 μg/ml lalrunculin A prevent these pronuclear events; these drugs will inhibit the apposition of the pronuclei at the egg center. In sea urchin eggs, colcemid or griseofulvin treatment doe? not result in the same effect and the male pronucleus forms with the attendant accumulation of the nuclear lamins. The differences in the requirement for microtubule assembly during pronucleus formation may be related to the cell cycle: In mice the sperm enters a meiotic cytoplasm, whereas in sea urchin eggs it enters an interphase cytoplasm. Refertilization of mitotic sea urchin eggs was performed to test the possibility that this phenomenon is related to whether the sperm enters a meiotic/mitotic cytoplasm or one at interphase; during refertilization at first mitosis, the incorporated sperm nucleus is unable to decondense and acquire lamins. These results indicate a requirement for microtubule assembly for the progression from meiosis to first interphase during mouse fertilization and suggest that the cytoskeleton is required for changes in nuclear architecture necessary during fertilization and the cell cycle.     

Duplication of an Xp segment that includes the ZFX locus causes sex inversion in man

Summary Two 46,XY females with tandem duplications of an X short arm segment were studied by cytogenetic and Southern blot analysis. The results show that the duplicated segment in each case included the Xp21.2–Xp22.2 interval, resulting in a double dose of ZFX on the single active X chromosome. The results from our two cases, in conjunction with those reported by other workers, lead us to conclude that the duplication is the reason for the sex inversion. If ZFY and ZFX are indeed sex-determining gene loci, these findings favour a model of sex determination characterized by antagonistic interaction between these genes.     

Fine structure of external ‘genital’ papillae in the fresh water miteHydrovolzia placophora (Hydrovolziidae,Actinedida, Actinotrichida,Acari)

Numerous genital papillae are described for the first time in the freshwater miteHydrovoliza placophora. In contrast to other actinotrichid mites, these organs are located on the epimeral plates, thus well removed from the genital opening. Ultrastructurally, the papillae correspond to those of other freshwater mites and are thus likely involved in ion/osmoregulation.     

Molecular analysis of theArabidopsis pattern formation geneGNOM: gene structure and intragenic complementation

TheGNOM gene is required for pattern formation along the main body axis of the embryo in the flowering plantArabidopsis thaliana. Mutations in theGNOM gene alter the asymmetric division of the zygote and interfere with the formation of distinct apical-basal regions in the developing embryo. We have isolated theGNOM gene by positional cloning, characterised its structure and determined the molecular lesions in mutant alleles. Although the predicted 163 kDa GNOM protein has a conserved domain in common with the yeast secretory protein Sec7p, it is most closely related in size and overall similarity to the product of the yeastYEC2 gene, which is not essential for cell viability. Four fully complementinggnom alleles carry missense mutations in conserved regions, seven partially complementing alleles have premature stop codon mutations and two non-complementing alleles have splice-site lesions. Our results suggest that the GNOM protein acts as a complex of identical subunits and that partial complementation may involve low levels of full-length protein generated by inefficient translational read-through.Communicated by H. Saedler     

HSP25 in isolated perfused rat hearts: Localization and response to hyperthermia

Recent investigations concentrate on the correlation between the myocardial expression of the inducible 70-kDa heat shock protein (HSP70i) by different stress conditions and its possible protective effects. Only few studies have focused on the involvement of small heat shock proteins in this process. We analyzed the location of the small heat shock protein HSP25 in isolated cardiomyocytes as well as its location and induction in isolated perfused hearts of rats. By immunofluorescence microscopy HSP25 was found to colocalize with actin in the I-band of myofibrils in cardiomyocytes of isolated perfused hearts as well as in isolated neonatal and adult cardiomyocytes. Hyperthermic perfusion of isolated hearts for 45 min resulted in modulation of different parameters of heart function and in induction of HSP25 and HSP70i. Temperatures higher than 43°C (44–46°C) were lethal with respect to the contractile function of the hearts. Compared to control hearts perfused at 37°C, significant increases during hyperthermic perfusion at 42°C and 43°C were obtained for heart rate, contraction velocity and relaxation velocity. In response to hyperthermia at 43°C and after subsequent normothermic perfusion for 135 min at 37°C, left ventricular pressure, contraction velocity and relaxation velocity remained significantly elevated. However, heart rate returned to control values immediately after the period of heat treatment. HSP25 is constitutively expressed even in normothermic perfused hearts as shown by Western blotting. Hyperthermia increased the content of HSP25 only in the left ventricular tissue. In contrast, HSP70i was strongly induced in all analyzed parts of the myocardium (left ventricle, right ventricle, septum). Our findings suggest a differential regulation of HSP25 and HSP70i expression in response to hyperthermia in isolated perfused hearts. The constitutively expressed HSP25 seems to be located adjacent to the myofibrils which implies a specific role of this protein even under unstressed conditions for the contractile function of the myocardium.     

Influence of glycosylation inhibitors on dihydropyridine binding to cardiac cells

In primary cultures of neonatal rat heart cells we found a linear correlation between the number of L-type calcium channel-specific dihydropyridine (DHP) binding sites and spontaneous beating frequency (v).Formation of glycoproteins in tissue culture was suppressed by different inhibitors of N-glycosylation. This inhibition alters to a different extent the binding of the DHP ligand (+)-[methyl-³H]PN 200-110 and v. The most severe but reversible effect occurs at 6 g/ml tunicamycin (B_max 45% and v 6%, resp., of control), a slight increase in B_max at 0.1–0.5 mM castanospermine and 0.05–2.5 mM deoxymannojirimycin. The other inhibitors gave no significant alterations of B_max.     

Post-mortem behaviour of Early Paleozoic nautiloids and paleobathymetry

It is unlikely that the intact or commonly preserved varieties of Ordovician-Silurian nautiloid shells were able to drift for any distance at the surface of the sea even if they died there. Their cameral capacity was much larger than the volume of the extracted or decayed body, and it would have contained a partial vacuum and cameral liquid when they were alive. The closely spaced and thin septa of the shallow-water adapted species were liable to buckle in compression and then implode in local tension during reverse hydrostatic loading by water pressure. This reverse loading and internal implosion of the septa was probably initiated by the sudden cameral refilling of an apical chamber caused by the depositional rupture of the apical siphuncle at or near the maximum habitat depth of these species. The instantaneous buckling of the more adorai septa was potentially terminated by variations in the septum thickness and cameral fill-fractions at that time, and they imply that some of the Silurian nautiloids from Bohemia were deposited at a minimum depth of about 65 m. Alternative interpretations involving the breakage of the same septa in tension, or buckling due to the difference in pressure between adjacent flooded chambers, set a maximum depth limit of about 160 m for the same facies. Many of the smaller Silurian nautiloids were unlikely to buckle during refilling, and they were potentially flooded faster than they could sink, below a depth of 100–300 m.