摘要:

AbstractSeveral larval stages of the dipteranChironomus thummiwere treated with a synthetic juvenile hormone (JH) mixture. Treatment resulted in larvae which underwent the first three molts, but thereafter development was arrested; many were incapable of completing the larval‐pupal molt. The pattern of chromosomal puffs in the prepupal salivary gland was examined at 91 loci: nine pupal puffs which were consistently active in controls were found to be reduced following treatment; one puff, Balbiani ring IV b, was enlarged. Autoradiographs indicate intensive RNA synthesis at Balbiani ring IV b, but depressed synthesis at the other nine affected loci. The puffing pattern demonstrates for the first time in detail specific effects of chemical compounds with JH activity on chromosomal puffs. Compounds exhibiting JH activity may regulate transcriptional activity at specific gene loci, and specific alterations in RNA synthesis may account for alterations in the course of metamorphosi

ISSN:0022-104X    

DOI:10.1002/jez.1401730402

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

年代:1970

数据来源: WILEY

摘要:

AbstractElectrophysiologic analyses of cultures of various combinations of spinal cord and skeletal muscle tissues demonstrate that characteristic neuromuscular transmission can develop and be maintained for monthsin vitro. The studies include: (1) cultures of mouse embryo spinal cord with attached myotomes, explanted prior to formation of neuromuscular junctions, and (2)in vitro‐coupled fetal rodent cord and muscle explants, in which one tissue is grown in isolation before presentation of the other explant (0.5–1 mm apart).After innervation occurs during the first few weeksin vitro, selective stimulation of spinal cord evokes widespread synchronized twitches in the muscle tissue. Simultaneous microelectrode recordings of cord and muscle responses to local cord stimuli show that muscle action potentials generally occur with latencies of several msec after onset of cord discharges. Rhythmic spontaneous bursts of muscle potentials (and contractions) occur, at times, in close correlation with periodic cord discharges.d‐Tubocurarine (1–10 μg/ml) selectively blocks neurally evoked muscle contractions while electric stimuli applied directly to the muscle fibers are still effective. Many apparently non‐innervated fibers, on the other hand, show sporadic, asynchronous fibrillations which are not altered by cord stimuli nor blocked by curare.Eserine and strychnine produce characteristic increases in repetitive muscle activities related to the primary site of action of these pharmacologic agents.Cultured neuromuscular tissues can, then, provide a valuable model system for correlative physiologic and cytologic studies of nerve and muscle cells during critical stages of maturation and formation of intercellular relationships under isolated conditio

ISSN:0022-104X    

DOI:10.1002/jez.1401730403

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

年代:1970

数据来源: WILEY

摘要:

AbstractThe distribution of interstitial cells and I‐cell derivatives in hydra is asymmetrical. This asymmetry is expressed apico‐basally along the stalk and radially with respect to cell layer. An inductive factor concentrated from the tissues of hydra alters this expression of polarity (Lesh and Burnett, '66).To test the hypothesis that quantitative differences in the concentration of this inducer effect qualitative differences in I‐cell differentiation, regenerating annuli were exposed to tissue extracts containing varying levels of inductive activity. Two types of extracts were employed: (1) serial dilutions of an active extract; and (2) extracts from different species of hydra exhibiting decreasing levels of inductive capacity.Hydra pirardiannuli were incubated four hours in extract. After 24 hours annuli were fixed, sectioned, stained, and counts made of all cell types.Statistical analyses of these counts show that responding cell types demonstrate one or both of two responses: proliferation and/or differentiation. The initial response in normal annuli is a 1.9 ± fold increase in the proportion of I‐cells present. Annuli which undergo an increase in I‐cell complement before incubation develop alterations in the distribution of I‐cell derivatives. At concentrated inducer levels isorhiza cnidocytes (epidermis) and mucus cells (gastrodermis) differentiate. At lower concentrations stenotele cnidocytes and gland cells appear. The distribution of epithelio‐muscular cells and digestive cells (not I‐cell derivatives) is independent of inducer concentration.Also, the distribution of I‐cells and derivatives found after the experimental treatments coincides directly with the distribution of these cell types relative to the inductive regio

ISSN:0022-104X    

DOI:10.1002/jez.1401730404

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

年代:1970

数据来源: WILEY

摘要:

AbstractThe differentiation of cartilage and bone from common germinal cells on the membrane bones of the embryonic chick has been investigated to test the hypothesis that acid mucopolysaccharides (chondroitin sulphate) and collagen play a role in controlling the pathways of differentiation open to the germinal cells. Injection of cortisone acetate was used to suppress sulphation of chondroitin to chondroitin sulphate and injection of vitamin C to stimulate collagen synthesis. Of the membrane bones studied 60–80% exhibited suppression of chondrogenesis, indicating that chondroitin sulphate and/or collagen play important roles in the control of chondrogenesis.Mechanical stimulation and hypoxia have been related to chondroitin sulphate synthesis in proposing a mechanism to explain the differentiation of cartilage and bone from common germinal cell

ISSN:0022-104X    

DOI:10.1002/jez.1401730405

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

年代:1970

数据来源: WILEY

摘要:

AbstractThe differential adhesion hypothesis attributes sorting‐out behavior of embryonic cells to differences in the strengths of their intercellular adhesions. It suggests that cells in mixed populations rearrange themselves to minimize their total adhesive free energy. The final configuration adopted is viewed as approaching a moststable or equilibrium configuration, with the less cohesive cell/population tending to envelop the more cohesive one.The hypothesis enables two predictions to be made. First, if the final configuration adopted by a mixed cell population indeed approximates an equilibrium configuration, the same final configuration should be approached irrespective of the starting configuration. Second, comparison of the equilibrium configurations for all possible pair‐combinations of a series of cell populations of different types should reveal a hierarchy of “preference” for the internal position, reflecting a hierarchy of cellular cohesiveness.These predictions have been tested and confirmed. First, any particular pair of tissues approaches the same final configuration, irrepective of whether the cells are initially randomly intermixed or tissue fragments are laterally joined. Second, the predicted hierarchy of preference for the internal position has been found, consistent with a hierarchy of cellular cohesiveness.An effort has been made to clarify confusions that have arisen concerning the differential adhesion hypothesis. It is particularly stressed that the hypothesis offers an explanation for cell population behavior in terms of relative strengths of cell adhesions and makes no proposals concernnig the chemistry of adhesion. However, the value of equilibrium configurations in guiding biochemical investigations of cell surface adhesives is pointed out, as is the relevance of the present observations to natural morphogenetic

ISSN:0022-104X    

DOI:10.1002/jez.1401730406

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

年代:1970

数据来源: WILEY

ISSN:0022-104X    

DOI:10.1002/jez.1401730401

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

年代:1970

数据来源: WILEY