CulB, a putative ubiquitin ligase subunit, regulates prestalk cell differentiation and morphogenesis in Dictyostelium spp.
Dictyostelium amoebae accomplish a starvation-induced developmental process by aggregating into a mound and forming a single fruiting body with terminally differentiated spores and stalk cells. culB was identified as the gene disrupted in a developmental mutant with an aberrant prestalk cell differentiation phenotype. The culB gene product appears to be a homolog of the cullin family of proteins that are known to be involved in ubiquitin-mediated protein degradation. The culB mutants form supernumerary prestalk tips atop each developing mound that result in the formation of multiple small fruiting bodies. The prestalk-specific gene ecmA is expressed precociously in culB mutants, suggesting that prestalk cell differentiation occurs earlier than normal. In addition, when culB mutant cells are mixed with wild-type cells, they display a cell-autonomous propensity to form stalk cells. Thus, CulB appears to ensure that the proper number of prestalk cells differentiate at the appropriate time in development. Activation of cyclic AMP-dependent protein kinase (PKA) by disruption of the regulatory subunit gene (pkaR) or by overexpression of the catalytic subunit gene (pkaC) enhances the prestalk/stalk cell differentiation phenotype of the culB mutant. For example, culB- pkaR- cells form stalk cells without obvious multicellular morphogenesis and are more sensitive to the prestalk O (pstO) cell inducer DIF-1. The sensitized condition of PKA activation reveals that CulB may govern prestalk cell differentiation in Dictyostelium, in part by controlling the sensitivity of cells to DIF-1, possibly by regulating the levels of one or more proteins that are rate limiting for prestalk differentiation.
Wang
Bin
B
Vema and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas 77030, USA.
Kuspa
Adam
A
D000595:Amino Acid Sequence; D000818:Animals; D002454:Cell Differentiation / Q000502:physiology*; D017931:DNA Primers; D004023:Dictyostelium / Q000166:cytology* / Q000502:physiology*; D017930:Genes, Reporter; D049452:Green Fluorescent Proteins; D008025:Ligases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008164:Luminescent Proteins / Q000235:genetics; D008969:Molecular Sequence Data; D009024:Morphogenesis / Q000502:physiology*; D016254:Mutagenesis, Insertional; D016133:Polymerase Chain Reaction; D021122:Protein Subunits; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D016415:Sequence Alignment; D025801:Ubiquitin / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases
D017931:DNA Primers; D008164:Luminescent Proteins; D021122:Protein Subunits; D011994:Recombinant Proteins; D025801:Ubiquitin; D049452:Green Fluorescent Proteins; D044767:Ubiquitin-Protein Ligases; D008025:Ligases