RESUMO
In the animal kingdom, maternal control of early development is a common feature. The onset of zygotic control over early development, defined as the maternal to zygotic transition (MZT), follows fertilization with a delay of a variable number of cell divisions, depending on the species. The MZT has been well defined in animals, but investigations remain in their infancy in plants. Recent evidence suggests, however, that in plants as in animals, the MZT also occurs several division cycles after fertilization. The likely convergent evolution of the MZT in the animal and plant kingdoms is fascinating and raises major questions regarding its biological significance, particularly with regard to its importance in genome reprogramming and the acquisition of totipotency by the embryo.
Assuntos
Sementes/fisiologia , Zigoto/fisiologia , Animais , Arabidopsis/embriologia , Arabidopsis/genética , Arabidopsis/fisiologia , Drosophila/embriologia , Drosophila/genética , Drosophila/fisiologia , Desenvolvimento Embrionário/genética , Feminino , Fertilização , Regulação da Expressão Gênica no Desenvolvimento , Regulação da Expressão Gênica de Plantas , Masculino , Camundongos , Modelos Biológicos , GravidezRESUMO
Most plant cells are characterized by the presence of a large central vacuole that in differentiated cells accounts for more than 90% of the total volume. We have undertaken a genetic screen to look for mutants that are affected in the formation of vacuoles in plants. In this study, we report that inactivation of the Arabidopsis gene VACUOLELESS1 (VCL1) blocks vacuole formation and alters the pattern of cell division orientation and cell elongation in the embryo. Consistent with a role in vacuole biogenesis, we show that VCL1 encodes the Arabidopsis ortholog of yeast Vps16p. In contrast to yeast mutants that lack a vacuolar compartment but are viable and morphologically normal, loss of the plant vacuole leads to aberrant morphogenesis and embryonic lethality.
Assuntos
Proteínas de Arabidopsis , Arabidopsis/genética , Proteínas de Membrana , Proteínas de Plantas/genética , Proteínas de Plantas/fisiologia , Proteínas de Saccharomyces cerevisiae , Vacúolos/metabolismo , Alelos , Arabidopsis/química , Divisão Celular , Membrana Celular/metabolismo , Clonagem Molecular , DNA/metabolismo , Proteínas Fúngicas/química , Proteínas Fúngicas/fisiologia , Teste de Complementação Genética , Dados de Sequência Molecular , Mutação , Fenótipo , Proteínas de Plantas/química , Transporte Proteico , Proteínas de Transporte VesicularRESUMO
Positional (or map-based) cloning techniques are widely used to identify the protein products of genes defined by mutation. In Arabidopsis the information generated by the Genome Initiative is giving this approach a decisive boost. A wealth of sequence polymorphisms and molecular markers is now available and can be exploited for fine mapping with technically simple and robust polymerase chain reaction-based methods. As a result it has become possible to complete positional cloning projects in a short time and with relatively little effort.
Assuntos
Arabidopsis/genética , Genoma de Planta , Mapeamento Físico do Cromossomo , Mapeamento Cromossômico , Clonagem Molecular , Polimorfismo GenéticoRESUMO
The EMB30 gene is involved in apical-basal pattern formation in the Arabidopsis embryo. Mutations in this locus produce mutants with a wide range of seedling phenotypes, but all of the mutants lack a root and a true hypocotyl. We have cloned the EMB30 gene, and it encodes a protein that has similarity to the yeast Sec7 protein and to two other open reading frames identified in clones from humans and C. elegans. We refer to the region of similarity among these four sequences as the Sec7 domain. The emb30-1 allele has a mutation in the Sec7 domain that alters a residue conserved in all four of these sequences, suggesting that this domain may be important for EMB30 function. Molecular data and microscopy studies of emb30 seedlings presented here indicate that EMB30 affects cell division, elongation, and adhesion and functions in seedling and adult plants as well as during embryogenic pattern formation.
Assuntos
Proteínas de Arabidopsis , Arabidopsis/genética , Moléculas de Adesão Celular/genética , Genes de Plantas , Fatores de Troca do Nucleotídeo Guanina , Reguladores de Crescimento de Plantas , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Sequência de Aminoácidos , Divisão Celular , Sequência Consenso , Expressão Gênica , Dados de Sequência Molecular , RNA Mensageiro/genética , Alinhamento de Sequência , Homologia de Sequência de Aminoácidos , Distribuição TecidualRESUMO
Following an earlier report, the article offers additional points concerning visual images observed after enucleation. These concern: (i) the relationship between field-cut due to the lesion before surgery and corresponding blank areas within the post-enucleation images; (ii) similarities in motion between the foveal images and foveally-fixated afterimages; (iii) possible correspondence of time course of the images to transneuronal atrophy and cell loss in human and monkey studies.
Assuntos
Procedimentos Cirúrgicos Oftalmológicos , Transtornos da Visão/fisiopatologia , Pós-Imagem , Neoplasias da Coroide/cirurgia , Percepção de Cores/fisiologia , Fóvea Central/fisiopatologia , Corpos Geniculados/fisiopatologia , Humanos , Melanoma/cirurgia , Campos Visuais , Percepção Visual/fisiologiaRESUMO
After enucleation of the right eye the author observed persistent and continuous visual images featuring angular groups of parallel-line segments which have continued for two years, to the present time, though considerably diminished. These phenomena are reported along with results of measurements of the images and of several simple experiments. Some quantitative comparisions are made to results from studies of macaque monkeys, and to human migraine fortification images.
