Control of Gene Expression

Nuclear processing of mRNA precursors in differentiating multicellular Dictyostelium discoideum aggregates is markedly slower than in growing amoebae. Synthesis of a protein can be regulated at many levels (9). During differentiation of Dictyostelium discoideum protein synthesis has been shown to be regulated at the levels of transcription, translation, and stability of the mRNA (22). We show here that the level of cytoplasmic mRNA in developing cells can also be regulated at the level of nuclear processing and transport to the cytoplasm.Differentiation of growing Dictyostelium amoebae is induced by amino acid starvation; an initial response to starvation is a preferential inhibition of translation of certain mRNAs (2). During and just after formation of multicellular aggregates, about 2,000 to 3,000 new species of mRNA appear on the polyribosomes (5). Induction of most of these mRNAs is at the transcriptional level (20,33). Many of these developmentally regulated RNAs are specifically labilized when the multicellular aggregates are disaggregated; the stability of many members of this class of mRNAs is specifically increased by high levels of extracellular cyclic AMP and possibly also by cell-cell contact (7,24,26).In growing cells processing of mRNA and rRNA is rapid; only a few minutes are required t Present address: Biologia Generale, 10126 Turin, Italy.for a newly synthesized mRNA or rRNA to be processed within the nucleus and exit into the cytoplasm (13, 23). There is no accumulation of nuclear precursor to rRNA, or of nuclear polyadenylated [poly(A)+] RNA. One of the predominant alterations in nucleic acid metabolism after induction of differentiation is a markedly reduced rate of nuclear RNA processing (17). Several nuclear pre-rRNAs are accumulated (4), and nuclear poly(A)+ RNA does not exit into the cytoplasm until 1 or 2 h after synthesis (14). Although we do not understand why the rate of processing, transport, or both, of nuclear premRNAs in multicellular aggregates is so slow, this system is an appropriate one in which to determine the limiting step in nuclear processing for individual mRNAs. We show here that in multicellular aggregates 50 to 100 min is required for most species of developmentally regulated mRNAs to be transported to the cytoplasm, whereas only 25 to 60 min is required for processing of most species of "common mRNAs," i.e., those synthesized during both growth and differentiation.One particular class of developmentally regulated mRNAs share sequences homologous to a set of repetitive DNA sequences (34). We show here that many of the poly(A)+ nuclear RNAs

mentioning

confidence: 61%

Different mRNAs have different nuclear transit times in Dictyostelium discoideum aggregates.

Mangiarotti¹,

Zuker²,

Chisholm³

et al. 1983

“…Many of these changes in biochemical phenotype have been shown to be the direct result of differential gene transcription during development (4,6,10,16). However, virtually nothing is known about the mechanisms and molecules controlling this differential transcription, and no specific regulatory genes or their products have been identified.…”

mentioning

confidence: 99%

“…An extremely detailed description exists of the qualitative and quantitative biochemical changes which accompany and underlie the multicellular development of the cellular slime mold Dictyostelium discoideum (16,30). Many of these changes in biochemical phenotype have been shown to be the direct result of differential gene transcription during development (4,6,10,16).…”

mentioning

confidence: 99%

Multiple regulatory genes control expression of a gene family during development of Dictyostelium discoideum.

Alexander¹,

Cibulsky²,

Cuneo³

1986

Mutant strains of Dictyostelium discoideum carrying dis mutations fail to transcribe specifically the family of developmentally regulated discoidin lectin genes during morphogenesis. The phenotypes of these mutants strongly suggested that the mutations reside in regulatory genes. Using these mutant strains, we showed that multiple regulatory genes are required for the expression of the lectin structural genes and that these regulatory genes (the dis+ alleles) act in trans to regulate this gene family. These regulatory genes fall into two complementation groups (disA and disB) and map to linkage groups II and m, respectively. A further regulatory locus was defined by the identification of an unlinked supressor gene, drsA (discoidin restoring), which is epistatic to disB, but not disA, and results in the restoration of lectin expression in cells carrying the disB mutation. Mutant cells carrying the drsA allele express the discoidin lectin gene family during growth and development, in contrast to wild-type cells which express it only during development. Therefore, the suppressor activity of the drsA allele appears to function by making the expression of the discoidin lectins constitutive and no longer strictly developmentally regulated. The data indicate that normal expression of the discoidin lectins is dependent on the sequential action of the disB+, drsA', and disA' gene products. Thus, we described an

“…Cell-cell contacts may also affect developmental gene expression in D. discoideum (23). We examined the expression of oa-mannosidase in the absence of cell-cell contacts by harvesting cells growing on bacteria and resuspending them in starvation buffer containing 2 mM EDTA, which has been shown to disrupt cell-cell contacts early in the developmental cycle (11).…”

Section: Resultsmentioning

confidence: 99%

Developmental regulation of the alpha-mannosidase gene in Dictyostelium discoideum: control is at the level of transcription and is affected by cell density.

Schatzle¹,

Rathi²,

Clarke³

et al. 1991

In Dictyostelium discoideum, there is a group of genes that are expressed following starvation and when exponentially growing cells reach high densities. We have examined the expression of one of these genes, a-mannosidase. Using an a-mannosidase cDNA probe in Northern (RNA) blot analysis, we have shown that the previously observed increase in a-mannosidase enzyme-specific activity during development is due to an increase in the levels of a-mannosidase mRNA. mRNA levels reach a maximum by 8 h of development and then begin to decline by 14 to 22 h. Using nuclear run-on analysis, we have found that this gene is regulated at the level of transcription. We also examined the effects of cell-cell contacts, cyclic AMP levels, and protein synthesis on expression of this gene and found that they were not critical in regulating its expression. However, cell density did play a major role in the expression of a-mannosidase. High cell density or the presence of buffer conditioned by high-density cells was sufficient to induce expression of a-mannosidase, indicating that this is one of the prestarvation response genes. Finally, the a-mannosidase gene was not expressed in aggregationnegative mutant strain HMW 404.