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  • 1
    Digitale Medien
    Digitale Medien
    Organelle differentiation in the chick blastoderm during hypoblast formation (1971)
    Springer
    Development genes and evolution 166 (1971), S. 287-299 
    Details
    ISSN: 1432-041X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary The ultrastructure of the chick blastoderm was examined at three developmental stages, from an unincubated single-layered system through hypoblast advancement to full hypoblast formation. With the onset of incubation the nucleolus changes from a loose network of intermingled pars fibrosa and pars granulosa into a compact body with a definite matrix material. The endoplasmic reticulum, mitochondria, and Golgi complex increase in complexity and volume. In blastoderms with a fully developed hypoblast a special asymmetrical endoplasmic reticulum becomes abundant. These data are analysed in relation to similar structural differentiation of the nucleolus, endoplasmic reticulum, Golgi complex and mitochondria in the embryonic development of other vertebrate groups. The above changes in organelle structure are noted in both the epi- and the hypoblast, although these organelles become more abundant in the former. In the intermediate stage no differences are noted between epiblast cells underlined by hypoblast and those of the anterior single-layered region. The above changes in the epiblast must therefore be related to age and not to contact with the advancing hypoblast. Previous studies mentioned in the text seem to indicate that the inducing effect of the hypoblast on the epiblast is exerted after its complete formation and not during its advancement. Our results in the organelle differentiation during hypoblast formation are in accordance with this hypothesis.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00650035
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  • 2
    Digitale Medien
    Digitale Medien
    Synaptonemal complexes, telomeric nucleoli and the karyosphere in achiasmatic oocyte meiosis of the carob moth (1982)
    Springer
    Chromosoma 87 (1982), S. 293-302 
    Details
    ISSN: 1432-0886
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract Synaptonemal complexes and telomeric nucleoli are involved in the spatial organization and regular distribution of homologous chromosomes in meiosis of the achiasmatic female carob moth. The bivalents are held together from zygotene to metaphase by the Synaptonemal complexes. These are attached to telomeric nucleoli which appear during early meiotic prophase and are unique to the oocyte. The telomeric nucleoli fuse during prophase and the chromosomes concentrate into a small karyosphere before prometaphase. During the final stages of prophase elements of the Synaptonemal complex are found in the periphery of the fibrillar region of the telomeric nucleoli.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00327631
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  • 3
    Digitale Medien
    Digitale Medien
    The effect of acute saline volume expansion on renal Na−K-ATPase (1985)
    Springer
    Pflügers Archiv 405 (1985), S. 170-172 
    Details
    ISSN: 1432-2013
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract To examine the role of Na-K-ATPase in the natriuresis that occurs after acute extracellular volume expansion, we performed acute clearance experiments and in vitro analysis of renal microsomal ATPase activity in rats receiving intravenous 0.9% sodium chloride (0.1 ml/100g bw/min). Despite increased absolute reabsorption of filtered sodium (196±8.1 vs. 165±11.4 uEq/min, p〈0.05), renal medullary microsomal Na-K-ATPase activity was decreased from 134±5.9 to 110±6.3 pmol Pi/mg protein/hour (p〈0.02). No changes occurred in cortical or papillary regions and Mg-ATPase was unaffected. Similar results were obtained after adding 4 mEq/l potassium chloride to the infusion to prevent any fall in serum K+. These data suggest that a considerable percentage of sodium reabsorption is suppressed in acutely volume expanded animals and it is proposed that this is mediated by inhibition of medullary Na-K-ATPase.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00584539
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  • 4
    Digitale Medien
    Digitale Medien
    The in vivo and in vitro effect of calmodulin antagonists on the renal actions of 25(OH) vitamin D3 in the rat (1989)
    Springer
    Pflügers Archiv 415 (1989), S. 372-380 
    Details
    ISSN: 1432-2013
    Schlagwort(e): Phosphaturia ; Parathyroid hormone ; 25 Hydroxy-vitamin D3 ; Trifluoperazine ; Adenylate cyclase ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Previous work from this laboratory has demonstrated that 25(OH) vitamin D3 [25(OH)D3] acutely suppresses the phosphaturic action of parathyroid hormone (PTH) and interferes with the PTH-induced activation of adenylate cyclase (AC). Calmodulin inhibitors block vitamin D-induced Ca2+ transport in the gut and phosphorus uptake in renal BBMV's. We have examined whether calmodulin antagonists affect the renal action of 25(OH)D3. Acute clearance experiments were performed in PTH-infused parathyroidectomized rats receiving 25(OH)D3 after pretreatment with trifluoperazine (TFP) or promethazine (P). In vitro PTH-induced activation of renal AC was also studied in membrane preparations from pretreated rats in the presence of 25(OH)D3. 25(OH)D3 reduced the PTH-stimulated increase in fractional excretion of phosphorus (CP/CIn) from 0.292±0.024 to 0.195±0.018 (p〈0.005) and urinary cAMP from 149.3±20.3 to 78.1±10.4 pmol/min (p〈0.01) and also blunted AC activation in vitro. TFP but not P abolished the effects of 25(OH)D3 both in vivo and in vitro. R 24571 also abolished the in vitro effect of 25(OH)D3. Thus, (1) TFP abolishes both the antiphosphaturic and the AC/cAMP-related actions of 25(OH)D3, (2) P does not have these effects, and (3) R 24571 abolishes the in vitro effect of 25(OH)D3. These results suggest that the antiphosphaturic effect of 25(OH)D3 acting via the AC/cAMP system may be calmodulin dependent.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00370890
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  • 5
    Digitale Medien
    Digitale Medien
    Differential basic nucleoprotein kinetics in the two kinds of lepidoptera spermatids: Nucleate (eupyrene) and anucleate (apyrene) (1982)
    Springer
    Chromosoma 85 (1982), S. 387-398 
    Details
    ISSN: 1432-0886
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract Normal lepidopteran males produce two kinds of spermatozoa: nucleate (eupyrene) and anucleate (apyrene). Eupyrene spermatozoa have the usual type of elongate nuclei. But in apyrene spermatids, the nuclei never elongate and the chromatin remains in a telophase-like condition until enucleation occurs. The study of the differential nucleoprotein kinetics of the two types of spermatids, using the fluorescent dye sulfoflavine, shows that: (1) In the elongate eupyrene nuclei, lysine-rich nucleoproteins are replaced by arginine-rich ones, while in the non-elongating apyrene nuclei only lysine-rich nucleoproteins are detected. However, nuclear elongation is not causally related to nucleoprotein transitions as transitions occur in the eupyrene spermatids after nuclear elongation. (2) The replacement of the nucleoproteins occurs in the eupyrene nuclei in a polarized manner. This may be correlated with the heterogeneous ultrastructural configuration of the chromatin fibers in elongating spermatid nuclei, as shown in other insect species. (3) Concomitantly with the eupyrene spermatid nucleoprotein transition, the cytoplasm of the head cyst cell shows an increasing amount of cytoplasmic lysine-rich proteins, while no such a phenomenon occurs in apyrene cysts. This differential pattern distribution may reflact functional differences among the two types of cysts and is probably related to the regulation of the dichotomy in lepidopteran spermatogenesis.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00330361
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  • 6
    Digitale Medien
    Digitale Medien
    Regular and irregular divisions of Lepidoptera spermatocytes as related to the speed of meiotic prophase (1986)
    Springer
    Chromosoma 93 (1986), S. 227-230 
    Details
    ISSN: 1432-0886
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract Lepidoptera males bear two kinds of meiotic divisions. One is regular (eupyrene) and leads to nucleate, fertilizing spermatozoa. The other (apyrene) shows metaphase I chromosomes clumping together into irregular masses which later split forming daughter cells with unbalanced sets of chromosomes which are eventually extruded from the cells; hence, the spermatids develop into anucleate spermatozoa of unknown function. The apyrene divisions are induced by a haemolymph factor which becomes functional towards pupation. Using incorporation of tritiated thymidine at the premeiotic S-phase as a marker for timing, it was found that the prophase of the apyrene spermatocyte is shorter than that of the eupyrene spermatocyte. It is proposed that meiosis-specific proteins cannot be synthesized during the shortened apyrene prophase and that this is correlated with the irregular chromosome behaviour during the subsequent metaphase-telophase of these spermatocytes.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00292742
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  • 7
    Digitale Medien
    Digitale Medien
    The regular divisions of the spermatocytes as related to a meiotic lysine-rich protein fraction (1982)
    Springer
    Chromosoma 85 (1982), S. 109-118 
    Details
    ISSN: 1432-0886
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract Lepidopteran primary spermatocytes are bipotential leading first to regular (eupyrene) and later to irregular (apyrene) meiotic divisions. The kinetics of the lysine-rich proteins during this dichotomous meiosis was studied using the fluorescent dye sulfoflavine. Throughout the spermatogonial divisions, the chromatin fluoresces while the cytoplasm remains unstained. Reversely, during the meiotic prophase, the cytoplasm fluoresces strongly while the nuclei show only a few weakly fluorescing structures. From premetaphase to telophase the meiotic chromosomes fluoresce strongly again. But during this period, only in the eupyrene cells the cytoplasm remains strongly fluorescent; the fluorescence vanishs in the cytoplasm of the apyrene spermatocytes. Thus, the regular (eupyrene) meiotic divisions and the presence of a lysine-rich protein fraction in the cytoplasm of the dividing spermatocytes of Lepidoptera, are probably related.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00344597
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  • 8
    Digitale Medien
    Digitale Medien
    Two different patterns of interrupted spermatogenesis in winter diapause and summer quiescence in the desert beetle, Omorgus freyi (1993)
    New York, NY : Wiley-Blackwell
    Journal of Morphology 218 (1993), S. 347-358 
    Details
    ISSN: 0362-2525
    Schlagwort(e): Life and Medical Sciences ; Cell & Developmental Biology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Medizin
    Notizen: Spermatogenesis discontinues during both adult reproductive diapause and quiescence in the flightless males of Omorgus freyi. During both types of dormancy, spermatogenesis discontinuity is a dynamic process involving an uninterrupted supply of primary spermatocytes that undergoes partial development and lyses before spermatozoa can be formed. Notwithstanding this common feature, the pattern of discontinuity differs between the two kinds of dormancy. During reproductive diapause, spermatozoa and late spermatids are the first cells that lyse; after diapause break, spermatozoa are produced anew. During quiescence, in contrast, the first indication of discontinuity is the degeneration of late primary spermatocytes; spermatozoa apparently remain intact for a while but eventually degenerate as well. Therefore, males returning to sexual activity after a short period of quiescence may still have spermatozoa capable of fertilization. However, following a long period of quiescence, spermatozoa will be absent and must be produced anew, as in postdiapausing males. The existence of two different patterns of spermatogenesis discontinuity may indicate that each is controlled differently by the endocrine system, in response to the different environmental conditions inducing quiescence or diapause. Dual control of discontinuity may contribute to the high reproductive potential of these flightless beetles, under unpredictable and extreme desert conditions. © 1993 Wiley-Liss, Inc.
    Zusätzliches Material: 18 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jmor.1052180309
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