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Expression of many developmentally regulated genes in Myxococcus depends on a sequence of cell interactions
1Department of Biochemistry, Stanford University School of Medicine, California 94305.
Abstract:
Certain developmental mutants of Myxococcus xanthus can be complemented extracellularly by wild-type cells. These mutants behave as if they are defective in cell-cell interactions that are required for development. There may be several different interactions because the mutants belong to four extracellular complementation groups (A, B, C, and D). We report here that B- and C- mutations change the pattern of gene expression during Myxococcus development as detected by transcriptional fusions to lacZ mediated by Tn5 lac. The mutant C locus reduced or abolished developmental beta-galactosidase expression from 15 lac fusions that normally begin to be expressed in wild-type cells after 6 hr of development. Expression of these C-dependent lac fusions was restored to C- mutants by adding wild-type cells. The C- mutation did not affect the expression of 10 lac fusions that normally begin to be expressed before 6 hr of development, indicating that the C-mediated cell-cell interaction is required beginning at about 6 hr of development. Cells require the B+ function very early in development because a B- mutation reduced or abolished developmental beta-galactosidase expression from all 26 lac fusions tested, including some that normally begin to be expressed at the onset of development. In a C- mutant and in a B- mutant, some lac fusions responded with reduced beta-galactosidase expression, whereas other fusions, which would normally begin beta-galactosidase expression at about the same time during development, expressed no beta-galactosidase, indicating that developmental genes within a given temporal class display different sensitivities to the absence of cell-cell interactions. Requirements for B+ and C+ function, as well as the previously described A+ function, appear to lie on the same developmental pathway.
Insights
Mutations in Myxococcus xanthus development disrupt cell-cell interactions, affecting gene expression timing. Wild-type cells can restore normal development in these mutants, highlighting crucial developmental pathways.
Area of Science:
- Microbiology
- Developmental Biology
- Molecular Genetics
Background:
- Myxococcus xanthus development relies on extracellular complementation between wild-type and mutant cells.
- Mutants defective in cell-cell interactions fall into four complementation groups (A, B, C, D).
Purpose of the Study:
- To investigate the role of extracellular complementation groups B and C in Myxococcus xanthus development.
- To determine how mutations in B and C affect gene expression patterns during development.
Main Methods:
- Utilized Tn5 lac transcriptional fusions to monitor beta-galactosidase expression during development.
- Assessed the impact of B- and C- mutations on the temporal expression of developmental genes.
- Complemented mutant strains with wild-type cells to observe rescue effects.
Main Results:
- The C- mutation impaired beta-galactosidase expression of 15 late-developing lac fusions, which was restored by wild-type cells.
- The B- mutation severely reduced or abolished expression of all 26 tested lac fusions, including early-developing ones.
- Developmental genes showed differential sensitivity to the absence of B+ and C+ functions, even within the same temporal class.
Conclusions:
- The B+ and C+ functions are essential for specific stages of Myxococcus xanthus development, influencing gene expression timing.
- Cell-cell interactions mediated by B+ and C+ functions are critical for regulating developmental gene expression.
- The B+, C+, and previously identified A+ functions likely operate within the same developmental pathway.