摘要:

AbstractIn this report the effects of cell density on the expression of differentiation by chick embryo sternal chondrocytes is studied. Differentiation is simultaneously assayed in terms of the rate of synthesis of collagen and acid mucopolysaccharide and in terms of the distribution of newly synthesized acid mucopolysaccharide between the cells and the culture medium. Cell density is studied first in terms of the number of cells per plate and second in terms of the size of aggregates of cells. First, when cultures, started‐with 104cells/60 mm dish, are studied over time, it is observed that the rate of synthesis of collagen and acid mucopolysaccharide increases faster than accountable for by the growth rate. Because conditioned medium placed on cultures grown in fresh medium can rapidly enhance mucopolysaccharide synthesis relative to the growth rate, it is suggested that conditioning of the culture medium might contribute in part to the observed rapid acceleration of the expression of differentiation with time in culture. Second, when cultures are started with small inocula so that large aggregates of cells form before cultures reach stationary phase, both the rate of synthesis of specialized products and the ability of cells to retain acid mucopolysaccharides is promoted. It is suggested that accumulated matrix might provide a microenvironment that itself promotes better expression of the cartilage phenotyp

ISSN:0022-104X    

DOI:10.1002/jez.1401870302

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY

摘要:

AbstractLarge numbers of mesogleal fibers are found in constricted regions ofChrysaorastrobilae. The mesoglea in these regions appears to be branched. Many fibers are oriented normal to the surfaces of gastrodermal cells. The mesoglea of non‐constricting regions contains similar fibers, most of which are not so oriented. Fibers and fiber bundles in the constricting regions may serve as a barrier to vertical cell migration, so that formation of ephyrae can occur. The fibers may also serve to stabilize constrictions once they are formed. Microfilament bundles, oriented transversely to the oral‐aboral axis, are present in the gastrodermis of scyphisto

ISSN:0022-104X    

DOI:10.1002/jez.1401870303

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY

摘要:

AbstractTemperature and prolactin were studied as control factors in the process of newt forelimb regeneration. Temperature was varied in five steps from 10° to 30°C under otherwise constant environmental conditions. Longitudinal new growth and limb differentiation were observed. Temperature was found to have a profound effect upon both developmental processes. Maximal longitudinal new growth resulting from changes in temperature alone occurred at 25°C with maximal limb differentiation at 30°C. At each temperature studied, prolactin enhanced both new growth and limb differentiation. With prolactin, maximum new growth also occurred at 25°C, but maximum limb differentiation occurred at 20°C. For our purposes optimum limb development was defined as the greatest new growth commensurate with full normal development. This optimum was reached by prolactin treated animals at 20°C when the regenerating limbs studied achieved 100% maximum normal differentiation and 87% maximum new growth. It was possible by employing a combination of temperature changes and hormone administration to control newt forelimb regeneration and produce a whole spectrum of limb devel

ISSN:0022-104X    

DOI:10.1002/jez.1401870304

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY

摘要:

AbstractHistological changes in planarian epidermis, as well as the differentiation of new epidermal cells during the course of differentiation, were studied with the electron microscope.Immediately after decapitation, pre‐existing epidermal cells of the area surrounding would stretch out over the cut‐surface and cover it completely with a thin film within 16 hours. However, these epidermal cells in the film were replaced by newly differentiated cells during the period extending from the second to sixth day of regeneration. Thus, after injury, the initial compensational closure is formed on the cut‐surface by the pre‐existing epidermal film, but the epidermis which is finally regenerated is formed by complete colonization of pre‐existing epidermis by newly differentiated epidermal cells. New epidermal and rhabdite‐forming cells were found not only in epidermis but also in the interior and sub‐epidermal regions of the blastema and in the old tissue close to the wound surface. Our observations suggest that ectodermally oriented cells, such as epidermal and rhabdite‐forming cells, originate from neoblasts at the anterior of the old body, close to its interface with the regeneration blastema; such neoblasts differentiate into rhabdite‐forming, or epidermal, cells as they migrate from the old somatic stump through the regeneration blastema into its epidermal surface layer. The characteristic polarity of epidermal cells appears in newly differentiated ones when they locate in the

ISSN:0022-104X    

DOI:10.1002/jez.1401870305

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY

摘要:

AbstractCrowding factors are those substances released by fish, which, under crowded conditions, inhibit both their growth and reproduction and depress their heart rate. We have partially purified the crowding factor from goldfish and carp by following a heart‐rate‐depression assay. The heart‐rate‐depression activity eluted with the diglyceride fraction from both silicic acid and Sephedex LH‐20. A slightly different activity eluted with the free sterols. The peak activity associated with the diglycerides has a distinctive ultraviolet spectrum distinguishable from that of phthalic acid esters, which are also active in the assay sytem and are found in fish tissues and f

ISSN:0022-104X    

DOI:10.1002/jez.1401870306

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY

摘要:

AbstractThe effects of dibutyryl cyclic AMP on the maturation of the mouse oocyte in vitro were studied. It was found that concentrations of 100 μg/ml or greater prevented germinal vesicle breakdown in more than 95% of the treated oocytes. The inhibition of maturation was found to be a reversible phenomenon. When oocytes were exposed to the drug after the completion of germinal vesicle breakdown, no effect of the drug was noted. Thus, dibutyryl cyclic AMP appears to effect only the initial stages of meiotic maturation in the mouse oocyte.Theophylline was also found to inhibit maturation, suggesting that increased levels of cyclic AMP in the oocyte may be the causative agent of the inhibition of maturation

ISSN:0022-104X    

DOI:10.1002/jez.1401870307

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY

摘要:

AbstractThe macronuclear cycle in regenerating posterior fragments of albinoBlepharisma intermediumconsists of four sequential stages which result in the reversible condensation of the macronucleus, and which are similar to those in the pigmented strain. Tritiated deoxyuridine incorporation occurs predominantly during the first three hours of regeneration and then declines. Of the early hours, hour 2 exhibits a significant increase in the proportion of heavily‐labeled cells. A statistical comparison of whole organisms labeled through exposure to radioactive precursor for a one‐hour period with fragments labeled at each hour of regeneration reveals a significantly greater number of labeled fragments for each of hours 1 through 4. Asynchronous patterns of DNA replication are evident in the macronucleus of both regenerating and whole cells. Oval‐shaped pellicular rings, consisting of dense accumulations of silver halide grains are evident during hours 5 and 6 of regeneration.Continuous inhibition of DNA synthesis during regeneration produces effects which depend upon the specific inhibitor employed. 5‐Aminouracil (AU) effects an appreciable delay of regeneration, without lethal or abnormal consequences. AU, hydroxyurea (HU), 5 bromodcoxyuridine (BUdR) and 5‐fluorodeoxyuridine (FUdR) exhibit a marked inhibitory effect upon division when they are administered to two‐hour fragments. The first three hours of regeneration is the period of greatest susceptibility to inhibitor action with respect to post‐regeneration division. AU, BUdR and FUdR interfere with the sequence of macronuclear events when these inhibitors are administered during hours 2–4 of regeneration. Contracted macronuclei are present at 24 hours and are related to division delay. HU, FUdR and BUdR treatment, during the later hours of regeneration, results in macronuclear fragmentation, branching and abnormal massing, respectively. Cytoplasmic abnormalities result from fragment exposure to the inhibitors during hours 4–6, with BUdR producing the most p

ISSN:0022-104X    

DOI:10.1002/jez.1401870308

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY

摘要:

AbstractIsolated brown bullhead catfish,Ictalurus nebulosus, were conditioned to discriminate between water samples from aquaria containing solitary conspecifics. Urine and extracts of urophyses, thoracic spinal cord, integument, gill and urinary bladder were then assayed to determine if they were active in effecting this discrimination. Urine and urophyseal extracts were consistently most active as sources of chemical information.

ISSN:0022-104X    

DOI:10.1002/jez.1401870309

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY

摘要:

AbstractMaternal effect mutations are useful tools which may aid in determining how the morphogenetic organization of the egg cytoplasm controls the plan of early development. One of the most interesting of the several maternal effect genes in the axolotl,Ambystoma mexicanum, is theogene. It is unique in that all embryos ofo/ofemales are affected in identical fashion, uniformly stopping development during gastrulation just when the main events of organ formation should be initiated. This paper is an investigation of the cytology, karyotype, and nucleic acid synthesis in mutant and control embryos and provides some important clues as to the mechanism of action of theo+gene. Cell division and DNA synthesis in mutant embryos are sharply reduced at the mid‐late blastula stage. At this time in normal embryos, RNA synthesis is activated but is not in embryos ofo/ofemales. The evidence from classical hybridization experiments and experiments with enucleated embryos suggests that this RNA synthesis is necessary for gastrular morphogenesis to take place. Thus the product of theo+gene, theo+substance, may be a stored regulator involved in genome activation during the late blastula stage which is required for the succeeding events of gastrulation. How it is involved in regulation remains to be worked ou

ISSN:0022-104X    

DOI:10.1002/jez.1401870310

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY

ISSN:0022-104X    

DOI:10.1002/jez.1401870301

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY