摘要:

AbstractThe organization of the 5S rRNA genes in the MACronuclear genome of Tetrahymena thermophila was examined during MAC development and replication. The 5S genes are arranged in several tandem arrays of alternating transcribed and spacer sequences in both MICronucleus and MAC. The number of EcoRI fragments bearing 5S gene clusters is similar in MIC and MAC. Most fragments occur in both the MIC and newly formed MAC genomes, a few being MIC‐limited and a few MAC‐limited. The same rearrangements are seen in the MACs of all four caryonides of a mating pair, and most rearrangements are seen in the newly formed MACs of different inbred strains. During replication of the MAC about half the fragments bearing 5S gene clusters disappear in different cell lines, and new fragments containing 5S genes appear. These fragments differ in size from those present in the MIC or newly formed MAC. These alterations occur in the MACs of all strains except strain B, which is more resistant to vegetative rearrangement. The losses and gains of fragments occur during clonal propagation of cell lines. The process begins by 35 fissions following conjugation, but once an alteration occurs, it is stably propagated. Clonal variation occurs with respect to which losses and gains occur, although a nonrandom distribution is seen among cell clones. We conclude that the alterations in MAC fragment size occur at two stages in the life cycle of Tetrahymena. The first stage occurs during conjugation, when the MAC develops from the MIC. The second stage becomes manifest during vegetative growth, when DNA replication occurs in the MAC and daughter molecules are distributed “amitotically” to daughter nuclei. The two‐stage character to MAC alterations for the 5S genes is interpreted in terms of the two steps previously described for MAC differentiation: determination and phenotypic assortment. Possible molecular mechanisms are also

ISSN:0192-253X    

DOI:10.1002/dvg.1020050402

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe compensatory response is a regulatory event influencing the redundancy of the ribosomal RNA cistrons (rDNAs) ofDrosophila melanogaster. In this report we attempt to demonstrate that the compensatory event and the thymidine analogue bromodeoxyuridine (BrdU) specifically interact. We conclude that the drug inhibits the compensatory response ofDrosophila melanogasterXO males and argue that the compensatory event is not the passive consequence of replicational dominance known to occur inDrosophilapolytene tissues.

ISSN:0192-253X    

DOI:10.1002/dvg.1020050403

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe patterns of protein synthesis are examined in the hypoblast and in the areas that comprise the epiblast, that is, the area opaca, the marginal zone, and the central area, during the blastula stage which marks the beginning of the interaction between the epiblast and hypoblast for induction of the primitive streak. The results demonstrate that there are distinct qualitative and quantitative differences in protein patterns in individual areas of blastoderm, the differences being most distinct between the hypoblast and any of the component areas of the epiblast. These differences in patterns of proteins suggest that the component areas of the chick blastula have already diverged to different developmental fates before any apparent morphogenetic differentiation, that is, the appearance of the primitive streak.

ISSN:0192-253X    

DOI:10.1002/dvg.1020050404

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

年代:1984

数据来源: WILEY

摘要:

AbstractExtreme and rapid changes in the synthesis of messenger RNAs and proteins accompany differentiation in wing tissues ofDrosophila. Of the six actin genes, at least three are expressed in wing cells, some during the most extreme changes in cell shape. However, different messages of the set appear, decay, and reappear on a regulated temporal program. These results show that actin expression is stage‐specific in a single cell typ

ISSN:0192-253X    

DOI:10.1002/dvg.1020050405

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

年代:1984

数据来源: WILEY

摘要:

AbstractAmoebae of the MyxomycetePhysarum polycephalumin the interphase state typically contain only one proflagellar apparatus in which the anterior kinetosome (anterior centriole) is attached to the microtubule organizing center 1 (mtoc 1). We built strains possessing more than one mtoc 1 and a variable number of anterior centrioles to allow the appearance of new structures. In 8% of the amoebae of these strains, the 1:1 attachment between the anterior centriole and the mtoc 1 is not always respected. In nine cases studied using tridimensional reconstructions from ultrastructural thin sections, the pattern of attachment was more complex. A mtoc 1 could be linked to several anterior centrioles, and/or reciprocally an anterior centriole could be linked to several mtoc 1. In one case, an anterior centriole was not linked to a mtoc 1 and in three cases, a single centriole exhibited anterior and posterior characteristics. These observations suggest that (1) each pair of centrioles constitutes a morphological and physiological entity that is distinct from the mitotic center (mtoc 1); (2) the attachment of the anterior centriole to the mtoc 1 occurs at the end of each mitosis; (3) there is an inductory process during the morphogenesis of the link between the anterior centriole and the mtoc 1; (4) the anterior characteristics of a centriole can be present in the absence of the link with the mtoc 1; (5) the anterior and posterior characteristics of a centriole are not exclusive of each other, ruling out the existence of a lineage corresponding to the anterior centriole and a lineage corresponding to the posterior centriole; and (6) the differences between anterior and posterior centrioles result from a maturation process.

ISSN:0192-253X    

DOI:10.1002/dvg.1020050406

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

年代:1984

数据来源: WILEY

ISSN:0192-253X    

DOI:10.1002/dvg.1020050407

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

年代:1984

数据来源: WILEY

ISSN:0192-253X    

DOI:10.1002/dvg.1020050408

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

年代:1984

数据来源: WILEY

ISSN:0192-253X    

DOI:10.1002/dvg.1020050401

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

年代:1984

数据来源: WILEY