RESUMO
We isolated a cDNA from Dictyostelium discoideum that encodes a 30 kDa protein with significant similarity to members of the major intrinsic protein (MIP) family of membrane transporters. The most closely related protein in the public data bases is an aquaporin from Cicadella viridis which shows 34% identity. The cDNA was used to isolate and characterize genomic fragments carrying the Dictyostelium gene which we named wacA. Genomic probes were used to recognize wacA mRNA isolated at various stages of development. The results showed that the gene is developmentally regulated such that the mRNA first appears at 12 h of development and is retained throughout the remainder of development. In situ hybridization of whole mounts prepared at 15 h of development showed that wacA mRNA accumulates exclusively in prespore cells and is absent from prestalk cells. Although wacA expression is prespore specific, disruption of the gene by homologous recombination did not result in observable alterations in the formation of spores or their resistance to osmotic challenges.
Assuntos
Aquaporinas , Dictyostelium/genética , Glicoproteínas de Membrana , Porinas/genética , Proteínas de Protozoários , Sequência de Aminoácidos , Animais , Mapeamento Cromossômico , Clonagem Molecular , Sondas de DNA/genética , Dictyostelium/crescimento & desenvolvimento , Proteínas do Olho/genética , Regulação da Expressão Gênica no Desenvolvimento , Regulação Fúngica da Expressão Gênica , Genes Fúngicos , Genes de Protozoários , Hibridização In Situ , Insetos/genética , Dados de Sequência Molecular , Pressão Osmótica , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Recombinação Genética , Homologia de Sequência de Aminoácidos , Esporos Fúngicos/genética , Esporos Fúngicos/crescimento & desenvolvimento , Esporos Fúngicos/metabolismoRESUMO
The steady-state relative population sizes of the several cell populations in Hydra attenuata were examined. In contrast to the constant average population size ratios between groups of animals, these ratios vary within limits between individual animals within a group. By maintaining animals on different feeding regimes (number of shrimp larvae ingested per day), the steady-state population size ratios were altered. The kinds of changes that occurred in these ratios suggest where controls may be operating to maintain the steady-state population sizes.
Assuntos
Hydra/citologia , Animais , Contagem de Células , Divisão Celular , Alimentos , Especificidade da Espécie , Fatores de TempoRESUMO
The distribution and dynamics of the 4 nematocyte populations of Hydra attenuata were investigated. Ninety-seven per cent of all nematocytes, including all 4 types, are mounted in the battery cells of the tentacles. The remaining 3%, including 2 types (stenoteles and holotrichous isorhizas) are mounted in the ectoderm of the body column. Eight-two per cent of all nematocytes are desmonemes; 11%, atrichous isorhizas; 5%, stenoteles; and 2%, holotrichous isorhizas. The density of each nematocyte population increases along the length of the tentacle towards the tip. The percentages of the total nematocytes per quarter of tentacle for each of the 4 quarters starting at the base is 15, 18, 25 and 42% respectively. The turnover time of the nematocyte populations in the tentacles was measured with 2 methods. First, the transit time for a carbon-marked battery cell from the base to the tip of the tentacle was measured. Secondly, the time required to replace the unlabelled nematocytes in the tentacles with [3H]proline-labelled nematocytes was measured. In both cases the time was 7--9 days. Based on these data (distribution and turnover time) a model was constructed for the dynamics of the nematocyte populations in the tentacles. The numbers of nematocytes produced dialy in the body column as predicted by the model are in reasonable agreement with the measured values.
Assuntos
Hydra/citologia , Animais , Movimento Celular , Células Epiteliais , Epitélio/fisiologia , Hydra/fisiologia , Cinética , Modelos BiológicosRESUMO
Mechanisms regulating the population size of the multipotent interstitial cell (i-cell) in Hydra attenuata were investigated. Treatment of animals with 3 cycles of a regime of 24 h in 10-2 M hydroxyurea (HU) alternated with 12 h in culture medium selectively killed 95-99% of the i-cells, but had little effect on the epithelial cells. The i-cell population recovered to the normal i-cell:epithelial cell ratio of I:I within 35 days. Continuous labelling experiments with [3H]thymidine indicate that the recovery of the i-cell population is not due to a change in the length of the cell cycle of either the epithelial cells or the interstitial cells. In control animals 60% of the i-cell population undergo division daily while 40% undergo differentiation. Quantification of the cell types of HU-treated animals indicates that a greater fraction of the i-cells were dividing and fewer differentiating into nematocytes during the first 2 weeks of the recovery after HU treatment. Therefore, the mechanism for recovery involves a shift of the 60:40 division:differentiation ratio of i-cells towards a higher fraction in division until the normal population size of the i-cells is regained. This homeostatic mechanism represents one of the influences affecting i-cell differentiation.
