摘要:

AbstractIn the heterothallic speciesNeurospora crassa, strains of opposite mating type,Aanda, must interact to give the series of events resulting in fruiting body formation, meiosis, and the generation of dormant ascospores. The mating type of a strain is specified by the DNA sequence it carries in the mating type region; strains that are otherwise isogenic can mate and produce ascospores. The DNA of theAandaregions have completely dissimilar sequences. Probing DNA from strains of each mating type with labelled sequences from theAand thearegions has shown that, unlike inSaccharomyces cerevisiae, only a single copy of a mating type sequence is present in a haploid genome. The failure to switch is explainable by the physical absence of DNA sequences characteristic of the opposite mating type. While the mating type sequences must be of the opposite kind for mating to occur in the sexual cycle, two strains of opposite mating type cannot form a stable heterokaryon during vegetative growth; instead, they fuse abortively to give a heterokaryon incompatibility reaction, which results in death of the cells along the fusion line. The DNA sequences responsible for this reaction are coextensive with those sequences in theAandaregions which are necessary to initiate fruiting body formation. The genusNeurosporaalso includes homothallic species – ones in which a single haploid nucleus carries all the information necessary to form fruiting bodies, undergo meiosis, and produce new haploid spores. One such species,N. terricola, contains one copy each of theAand theasequences within each haploid genome. Another homothallic species,N. africana, contains a single copy of theAsequence in the haploid genome, but does not contain any sequences corresponding to theasequence. We present a model for the role of the mating type‐specific sequences in heterothallic and homothallic species ofNeurosporaand we speculate on the origin of the different modes of reproduction in the genusNeurosp

ISSN:0265-9247    

DOI:10.1002/bies.950120202

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe retinoblastoma sensitivity protein (Rb) and the p53 gene product both appear to function as negative regulators of cell division or abnormal cellular growth in some differentiated cell types. Several types of cancers have been shown to be derived from cells that have extensively mutated both alleles of one or both of these genes, resulting in a loss‐of‐function mutation. In the case of the p53 gene, this mutational process appears to occur in two steps, with the first mutation at the p53 locus resulting in atrans‐dominant phenotype. The mutant p53 gene product enters into an oligomeric protein complex with the wild‐type p53 protein derived from the other normal allele and such a complex is inactive or less efficient in its negative regulation of growth control. This intermediate stage of carcinogenesis selects for the proliferation of cells with one mutant allele, enhancing the probability of obtaining a cancer cell with both alleles damaged.The DNA tumor viruses have evolved mechanisms to interact with the Rb and p53 negative regulators of cellular growth in order to enhance their own replication in growing cells. SV40 and adenovirus type 5 produce viral encoded proteins that also form oligomeric protein complexes with p53 and Rb, presumably inactivating their functions. These viral proteins are also the oncogene products of these viruses. Thus, the mechanisms by which cancer may arise in a host,viamutations or virus infections, have fundamental common pathways effecting the same cellular genes and gene products; Rb

ISSN:0265-9247    

DOI:10.1002/bies.950120203

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

年代:1990

数据来源: WILEY

摘要:

AbstractIn the 4 1/2 to 5 days between fertilization and implantation, the mouse conceptus must gain the abilities to implant and produce an embryo. Each of these is the sole developmental responsibility of one of two cell types forming the blastocyst, trophectoderm and inner cell mass (ICM), respectively. Trophectoderm is a polarized transporting epithelium while the ICM is an aggregate of non‐epithelial pluripotent stem cells. These two cell types originate from the division of polar blastomeres when their cleavage furrows parallel their apical surfaces. Blastomeres polarize in response to asymmetric cell–cell contact, and understanding the mechanism of this induction is regarded as the key to understanding the origin of trophectoderm and ICM. Here we propose a model based on transcellular ion current loops for the induction of cell polarity during the development of the first epithelium, trophectod

ISSN:0265-9247    

DOI:10.1002/bies.950120204

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

年代:1990

数据来源: WILEY

摘要:

AbstractDNA repair is important in such phenomena as carcinogenesis and aging. While much is known about DNA repair in single‐cell systems such as bacteria, yeast, and cultured mammalian cells, it is necessary to examine DNA repair in a developmental context in order to completely understand its processes in complex metazoa such as man. We present data to support the notion that proliferating cells from organ systems, tumors, and embryos have a greater DNA repair capacity than terminally differentiated, nonproliferating cells. Differential expression of repair genes and accessibility of chromatin to repair enzymes are considered as determinants in the developmental regulation of DNA repai

ISSN:0265-9247    

DOI:10.1002/bies.950120205

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe transcription of rat prolactin and growth hormone genesin vitrorequires a pituitary transcription factor, specific to certain cell types in the pituitary, which currently appears to be the PUF‐I/Pit‐1/GHF‐1 protein. This factor binds tocis‐regulatory elements in the 5′ region of both genes and exerts a positive influence on transcription initiation presumably by interacting with general transcription factors. The PUF‐I/Pit‐1/GHF‐1 transcriptional regulatory protein probably has an important role in not only the differentiation of the pituitary lactotroph/somatotroph cell lineage; it is also expressed in the early development of the nervous system but its function there is less well documented. It appears to be one member of a family oftrans‐activator proteins involved in differential gene expression in s

ISSN:0265-9247    

DOI:10.1002/bies.950120206

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

年代:1990

数据来源: WILEY

ISSN:0265-9247    

DOI:10.1002/bies.950120207

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

年代:1990

数据来源: WILEY

ISSN:0265-9247    

DOI:10.1002/bies.950120208

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

年代:1990

数据来源: WILEY

ISSN:0265-9247    

DOI:10.1002/bies.950120209

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

年代:1990

数据来源: WILEY

ISSN:0265-9247    

DOI:10.1002/bies.950120210

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

年代:1990

数据来源: WILEY

ISSN:0265-9247    

DOI:10.1002/bies.950120211

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

年代:1990

数据来源: WILEY