A gene expressed in undifferentiated vegetative Dictyostelium is repressed by developmental pulses of cAMP and reinduced during dedifferentiation.

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We describe the gene M4-1, whose unique pattern of developmental expression will allow us to study the molecular mechanisms controlling expression in undifferentiated cells in addition to repression in response to cAMP during development and reinduction during dedifferentiation. M4-1 is a Dictyostelium gene expressed in the undifferentiated cell. We have shown that M4-1 continues to be expressed very early during the developmental cycle but is repressed at a later stage of development, at a time coincident with the establishment of oscillations in the cAMP pool. Studies on the expression of the M4-1 gene in shaking culture, under conditions that mimic early development, have established that pulsatile stimulation of cells with cAMP is sufficient to repress M4-1 expression. Consistent with this, cells that are exposed to high levels of cAMP are unable to respond normally to cAMP oscillations and continue to express M4-1 at vegetative levels. These data indicate that low-level oscillations of cAMP are required for the repression of M4-1 expression rather than the continuous high levels of cAMP responsible for the regulation of a different class of Dictyostelium genes. We suggest that cAMP may mediate developmental expression of the Dictyostelium genome by different mechanisms. We also show that cell-cell interaction, a developmental event that occurs subsequent to the cAMP pulse, does not normally influence the regulation of M4-1. Finally, we have shown that when cAMP-pulsed cells are induced to dedifferentiate, M4-1 RNA sequences rapidly reappear in nuclei and cytoplasm, suggesting that regulation of M4-1 expression is primarily mediated at the level of transcription.

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