Bibliothek

Notizen: A study was made of 174 eggs recovered from 58 guinea pigs killed between the first and sixth days after mating, and the cytological details from the stage of sperm penetration to the pre-implantation blastocyst described. Eighty-nine percent of the expected number of eggs were recovered, and 97% of these were fertilized. Embryonic development proceeded from pronuclear and 2-cell eggs on day 1 to pre-implantation blastocysts on day 6, the duration of each of the early cleavage stages being of approximately 24 hours. No progressive loss of embryos was found over this period, all the eggs recovered on days 4, 5 and 6 being regarded as developing normally. Passage of embryos from the Fallopian tubes to the uterus commenced on the afternoon of day 3, and the majority of embryos entered the uterus shortly after this time at the stage of 8- to 16-cells. The tail of the fertilizing spermatozoon was detected in the cytoplasm of all eggs examined on day 1, in most of those examined on day 2, and frequently persisted up to the 8-cell stage. Three dispermic eggs, each containing two distinct cytoplasmic sperm tails, were found: one of these was at the pronuclear stage, the other two being considered of 4- and 6-cells respectively. Properties of adhesiveness were shown by blastocysts recovered shortly before implantation on day 6, but the characteristic “zona processes” were not seen.

Notizen: A Qβ RNA segment was produced in vitro by means of a synchronized minus-strand-directed synthesis using purified Qβ replicase, a reaction known to yield infectious Qβ RNA. Arguments are presented that a 5.5S product obtained by incubation for 30 seconds at 20°C corresponds to the 5′-terminal region of Qβ RNA. After obtaining and sequencing 26 T1 and 21 pancreatic RNase products, we established 3′ nearest neighbors by using products labeled with only one nucleoside [α-32P]triphosphate at a time. The ordering of the oligonucleotides was facilitated by observing the time of their appearance in products from incubations of 5, 10, 15, 20, and 25 seconds. The enzymatic product consists of 160 nucleotides; no known initiation triplet appears before the sixtieth nucleotide. There is no indication that the coat protein cistron starts within the RNA segment analyzed.

Notizen: The development of a virus is programmed by a series of negative and positive controls which determine the timing and the segment on either of the two DNA strands (l or r) to be transcribed into specific messenger RNA's. Bacteriophage λ provides one of the most deeply studied systems for following the development of lysogenic viruses. In the lysogenic repressed state, only 2-4% of the λ genome is expressed. This pc-cI-rex region is transcribed leftward to produce a repressor protein which prevents any further transcription by blocking the oL and oR operators flanking the cI-rex operon (figs. 1, 2). This negative control is relieved by destruction of the repressor, and the result is the “induction” of viral development. The earliest post-induction or postinfection events are the leftward transcription of the pLoL N region from strand l and the rightward transcription mainly of the pRoR-x segment from strand r. The N product acts as a positive control, permitting a leftward transcription beyond gene N and a rightward transcription of genes cII-O-P and also Q. The int-xis system controls the excision of the λ genome, whereas the act of rightward transcription and the products of genes O and P initiate the replication of λ DNA. The product of gene Q, still another positive control, stimulates rightward transcription of the late genes which control the synthesis and assembly of the phage heads and tails as well as cell lysis. Among other types of negative control are the possible competition between the two divergent transcriptions originating in region x, the “antirepressor” effect of the x product, and the interference between the two convergent transcriptions which collide in the central b2 region. The majority of controls are based on protein-DNA interactions and can be modified by mutations. For instance, transcription can be rendered independent of negative repressor control either by constitutive, v, mutations which decrease or abolish the affinity of the o operators for the repressor or by insertion of new promoters-e.g., c17 or ric- on the “downstream” side of the operator. The need for the positive N and Q controls may also be obviated by mutations in the N- or Q-dependent promoter or terminator elements.The specific DNA structure within the controlling sites is not known. However, a remarkable coincidence was observed; namely, the occurrence of pyrimidine-rich clusters in those segments of the individual DNA strands acting as templates for RNA synthesis. This observation, which pertains to all studied DNA's, including those of phages T2, T3, T4, T5, T6, T7, λ, and φ 80, formed the basis for a proposal that implicates pyrimidine-rich clusters in the initiation, control and/or termination of transcription, and also in the determination of the preferred strand and, consequently, the orientation of transcription. General considerations regarding the possible role of the structural singularities, especially those represented by the pyrimidine clusters, in the bipartite structure of the recognition regions in DNA are discussed.

Notizen: Cellular transformation was induced with avian myeloblastosis virus strain BAI-A (standard AMV) and with a strain of AMV containing subgroup B only. Cultures of muscle tissues from either chick embryo or day old chicks were used for this study. Results were similar in C/O and C/A cells. Leukemogenic virus was continuously produced by these transformed cultures.

Notizen: Growth of KB cells was inhibited by both spermine and spermidine, but the inhibition is reduced in conditioned medium. The amount of spermine required for 50% inhibition of plating varied according to the type of serum used with medium 199 (calf, fetal bovine, and horse; 0.55, 0.9, and 24 μg/ml respectively). The spermine oxidase activity of the three sera was calf 〉 horse 〉 fetal bovine, which is not the same ordering as was obtained for the inhibition. When the concentration of sera in the media was varied, the inhibition decreased as calf and fetal bovine sera concentration increased, whereas, with horse serum, an increase in serum concentration increased the inhibition. The opposite effects of increasing concentrations of the sera on the inhibition suggest that at least two factors are involved in the inhibition. A scheme which involves three factors (spermine oxidase, another enzyme and its activator) is postulated to account for the inhibitions and reversals observed. Spermine oxidase alone cannot account for the action of polyamine on cells.

Notizen: Inhibition of cellular respiration by treatment with the nonionic detergent Triton WR-1339 was found to be related to the cytotoxic response of cell to the surfactant. Respiration of sensitive cell lines (AV-3 and HeLa) markedly inhibited by Triton concentrations as low as 125 μgm/ml. Conditionally sensitive lines (BHK-21 and L-929) were affected by 500 μgm/ml while the respiration of insensitive cultures (primary rat and chick embryo cells) was unaffected by this concentration. Macrocyclon, a cyclic analogue of Triton, failed to alter the respiration rate of any of the above cell cultures.The levels of isocitric and succinic dehydrogenases in sensitive and conditionally sensitive cells were depressed within 2 hours after treatment with 500 μgm/ml of Triton was initiated and by 6 hours the activity was only 25% of the untreated controls. Similar results were obtained with mitochondrial preparations from these cells. Enzyme levels in insensitive cells were unaffected by Triton treatment.Mitochondrial damage was the most striking characteristic noted in treated cells examined by electron microscopy. The mitochondria were quite distorted and had lost most of their cristae formation. This mitochondrial damage was seen in all cell types examined although the rate at which it occurred varied. With sensitive cultures, damage was pronounced within 6 hours after the addition of Triton while mitochondria from conditionally sensitive cells were not grossly affected until 48 hours and they appeared to repair the damage following the removal of Triton.

Notizen: A structure for a generalized insect epidermal cell during the formation of the epicuticle is proposed, based on studies of several different epidermal cell types. The protein epicuticle is defined as the dense homogeneous layer below the cuticulin. The formation of the protein epicuticle involves secretory vesicles arising in Golgi complexes, and marks an interlude in the involvement in cuticle formation of plasma membrane plaques. The plaques are concerned in cuticulin formation before and in fibrous cuticle formation after the deposition of the protein epicuticle.The epidermis is characterized by the possession of a cytoskeleton of microtubules and a matrix of microfibers. In the elongated cells forming bristles and spines, the microfibers are often oriented in bundles with an axial banding which repeats every 120 Å. The microtubules are also arranged in columns with a trigonal packing and center to center spacing of about 800 Å. These cytoskeletal structures separate the other organelles into channels which may restrict the pathways open for the movement of secretory and pinocytotic vesicles. The protein epicuticle arises from the secretory vesicles which discharge at the apical surface. The contents disperse and reaggregate below the cuticulin. The Golgi complexes in the basal and central regions have many secretory vesicles and a small saccular component, differing from those nearer the apex which are smaller and have fenestrated saccules. The small coated vesicles (800 Å in diameter) associated with both sorts of complex, probably move to the apical and basal faces of the cell where they may give rise to the large coated vesicles (2000 Å in diameter) inserted in the plasma membrane. Pinocytosis occurs from both apical and basal faces but most lytic activity is in the apical region. Plant peroxidase injected into the haemocoel is taken up basally and transported to the apical MVBs. The large coated vesicles on the apical face may be concerned in the control of the extracellular subcuticular environment. They appear to fill up and detach, fusing to become the apical MVBs.

Notizen: Submandibular glands of the opossum have been studied by light and electron microscopy and compared with other mammalian salivary glands. The glands have four parenchymal segments which connect in the order named below to convey saliva toward the oral cavity. 1Secretory units are elongated branching tubules exhibiting mucous and special serous cell types. Mucous cells predominate and resemble those in other salivary glands. Special serous cells differ from “typical” serous cells. They contain a preponderance of tubular or vesicular endoplasmic reticulum and secretory granules which vary from electron lucent to electron opaque.2Intercalated ducts are short segments lined by nonsecretory, cuboidal cells.3Striated ducts are numerous and lie in the center of the lobule. The duct epithelium has four cell types, designated light cells, dark cells, Type I basal cells, and Type II basal cells. Light cells possess basal infoldings associated with mitochondria, but the other cell types lack this characteristic.4Excretory ducts are also lined by four cell types which bear the same names as those of striated ducts. Three of the four cell types are virtually identical to those of striated ducts, but light cells differ. They do not always contain basal infoldings and the supranuclear cytoplasm lacks distinct inner and outer zones.The glands resemble salivary glands of higher mammals in many respects while possessing certain unique cytological features which may reflect the secretory needs of the organism.

Notizen: The cytology of the vitellogenic stages in the development of the oocyte of Drosophila melanogaster has been studied using whole mounts and sections of plastic-embedded ovaries and single egg chambers for light microscopy and cytochemistry. The migrations, changes in morphology, and synthetic products of the follicle cells are described as a function of developmental stage. The follicle cells synthesize the egg coverings, the vitelline and chorionic membranes, and elaborate the micropyle and dorsal chorionic appendages. The changing structure of the nurse cell nucleus and changes in organelle composition of its cytoplasm are described. The nurse cells synthesize ribosomes, lipid droplets, and mitochondria. These components pass through the ring canal system into the oocyte, which increases in volume some 200,000 times during its 78 hours of development.

Notizen: Bovine parotid glands exhibit outstanding structural differences when compared with those of non-ruminant mammals. The acini are tortuous, branched and lined with cells of different heights, imparting a scalloped appearance to acinar lumina. Numerous microvilli, ca. 1.5 μ in length, extend into the lumina and intercellular canaliculi. Intercellular canaliculi measure ca. 3 μ in diameter and interweave in close association with intercellular tissue spaces. Intercellular tissue spaces are separated from the extraacinar spaces across a basal lamina only, whereas junctional complexes guard canaliculi from direct continuity with tissue spaces and/or extraacinar spaces. Flattened cytoplasmic lamellae extend from adjacent acinar cells and loosely interdigitate with one another across the tissue spaces. Acinar cells contain more mitochondria and less granular endoplasmic reticulum than parotid glands of non-ruminant mammals. Two types of secretory material, in the form of inclusions which vary in size and electron density, are present in the acinar cells. Intercalated ducts connect acini with striated ducts which in turn, empty into collecting ducts located between gland lobules. In terms of frequency of “basal infoldings” and numbers of mitochondria, striated ducts of calf parotid glands are not as well developed as those of certain other salivary glands. Myoepithelial cells are most often present at junctions of acini and intercalated ducts where they may attach to both acinar and ductal epithelium. Nerve “terminals” were not observed on the epithelial side of basement membranes in relation to the secretory cells.