ABSTRACT
In animal development, numerous cell-cell interactions are mediated by the GLP-1/LIN-12/NOTCH family of transmembrane receptors. These proteins function in a signaling pathway that appears to be conserved from nematodes to humans. We show here that the aph-2 gene is a new component of the GLP-1 signaling pathway in the early Caenorhabditis elegans embryo, and that proteins with sequence similarity to the APH-2 protein are found in Drosophila and vertebrates. During the GLP-1-mediated cell interactions in the C. elegans embryo, APH-2 is associated with the cell surfaces of both the signaling, and the responding, blastomeres. Analysis of chimeric embryos that are composed of aph-2(+) and aph-2(-) blastomeres suggests that aph-2(+) function may be provided by either the signaling or responding blastomere.
Subject(s)
Caenorhabditis elegans Proteins , Caenorhabditis elegans/embryology , Helminth Proteins/metabolism , Membrane Glycoproteins/metabolism , Membrane Proteins/metabolism , Signal Transduction , Amino Acid Sequence , Animals , Base Sequence , Blastomeres , DNA, Helminth , Helminth Proteins/genetics , Humans , Membrane Proteins/genetics , Molecular Sequence Data , Mutagenesis , Rabbits , Receptors, NotchABSTRACT
During Tetrahymena conjugation, programmed DNA degradation occurs in two separate nuclei. Thousands of germline-specific deletion elements are removed from the genome of the developing somatic macronucleus, and the old parental macronucleus is degraded by an apoptotic mechanism. An abundant polypeptide, Pdd1p (formerly p65), localizes to both of these nuclei at the time of DNA degradation. Here we report that, in developing macronuclei, Pdd1p localizes to electron-dense, heterochromatic structures that contain germline-specific deletion elements. Pdd1p also associates with parental macronuclei during terminal stages of apoptosis. Sequencing of the PDD1 gene reveals it to be a member of the chromodomain family, suggesting a molecular link between heterochromatin assembly and programmed DNA degradation.
Subject(s)
DNA, Protozoan/genetics , Genes, Protozoan/genetics , Heterochromatin/metabolism , Nuclear Proteins/physiology , Phosphoproteins/physiology , Protozoan Proteins , Tetrahymena thermophila/genetics , Amino Acid Sequence , Animals , Apoptosis/genetics , Cell Nucleus/chemistry , Cloning, Molecular , Conjugation, Genetic/physiology , DNA, Protozoan/metabolism , Gene Expression Regulation, Developmental , Germ Cells , Heterochromatin/chemistry , Micronucleus, Germline/chemistry , Molecular Sequence Data , Nuclear Proteins/analysis , Nuclear Proteins/genetics , Nuclear Proteins/isolation & purification , Phosphoproteins/analysis , Phosphoproteins/genetics , Phosphoproteins/isolation & purification , Protein Biosynthesis , Sequence Analysis , Sequence Analysis, DNA , Sequence Deletion , Tetrahymena thermophila/cytology , Tetrahymena thermophila/growth & developmentABSTRACT
During the 4-cell stage of C. elegans embryogenesis, the P2 blastomere provides a signal that allows two initially equivalent sister blastomeres, called ABa and ABp, to adopt different fates. Preventing P2 signalling in wild-type embryos results in defects in ABp development that are similar to those caused by mutations in the glp-1 and apx-1 genes, which are homologs of the Drosophila genes Notch and Delta, respectively. Previous studies have shown that GLP-1 protein is expressed in 4-cell stage embryos in both ABa and ABp. In this report, we show that APX-1 protein is expressed in the P2 blastomere and that a temperature-sensitive apx-1 mutant has a temperature-sensitive period between the 4-cell and 8-cell stages. We propose that APX-1 is part or all of the P2 signal that induces ABp to adopt a fate different than ABa.
