ABSTRACT
The Notch pathway is the key signal for many cell fate decisions in the nematode Caenorhabditis elegans including the uterine pi cell fate, crucial for a proper uterine-vulval connection and egg laying. Expression of the egl-13 SOX domain transcription factor is specifically upregulated upon induction of the pi lineage and not in response to other LIN-12/Notch-mediated decisions. We determined that dual regulation by LIN-12 and FOS-1 is required for egl-13 expression at specification and for complete rescue of egl-13 mutants. We found that fos-1 mutants exhibit uterine defects and fail to express pi markers. We show that FOS-1 is expressed at pi cell specification and can bind in vitro to egl-13 upstream regulatory sequence (URS) as a heterodimer with C. elegans Jun.
Subject(s)
Body Patterning/genetics , Caenorhabditis elegans Proteins/physiology , Caenorhabditis elegans/embryology , Caenorhabditis elegans/genetics , Membrane Proteins/physiology , Myoblasts, Smooth Muscle/physiology , Proto-Oncogene Proteins c-fos/physiology , Receptor, Notch1/physiology , Transcription Factors/physiology , Uterus/embryology , Animals , Binding Sites , Caenorhabditis elegans Proteins/genetics , Caenorhabditis elegans Proteins/metabolism , Cell Differentiation/genetics , DNA-Binding Proteins/metabolism , Disorders of Sex Development/embryology , Disorders of Sex Development/genetics , Enhancer Elements, Genetic , Female , Gene Expression Regulation , Models, Biological , Myoblasts, Smooth Muscle/metabolism , Oncogene Protein p65(gag-jun)/metabolism , Proto-Oncogene Proteins c-fos/metabolism , Receptors, Notch , Transcription Factors/genetics , Transcription Factors/metabolism , Uterus/metabolismABSTRACT
Cell fusion is fundamental for reproduction and organ formation. Fusion between most C. elegans epithelial cells is mediated by the EFF-1 fusogen. However, fusion between the anchor cell and the utse syncytium that establishes a continuous uterine-vulval tube proceeds normally in eff-1 mutants. By isolating mutants where the anchor-cell fails to fuse, we identified aff-1. AFF-1 ectopic expression results in fusion of cells that normally do not fuse in C. elegans. The fusogen activity of AFF-1 was further confirmed by its ability to fuse heterologous cells. AFF-1 and EFF-1 differ in their fusogenic activity and expression patterns but share eight conserved predicted disulfide bonds in their ectodomains, including a putative TGF-beta-type-I-Receptor domain. We found that FOS-1, the Fos transcription factor ortholog that controls anchor-cell invasion during nematode development, is a specific activator of aff-1-mediated anchor-cell fusion. Thus, FOS-1 links cell invasion and fusion in a developmental cascade.
Subject(s)
Caenorhabditis elegans Proteins/metabolism , Caenorhabditis elegans/cytology , Caenorhabditis elegans/metabolism , Proto-Oncogene Proteins c-fos/metabolism , Transcription Factors/metabolism , Amino Acid Sequence , Animals , Caenorhabditis elegans/embryology , Caenorhabditis elegans Proteins/chemistry , Cell Fusion , Cytoplasm/metabolism , Embryo, Nonmammalian/cytology , Epithelial Cells/cytology , Female , Insecta/cytology , Models, Biological , Molecular Sequence Data , Mutation/genetics , Phenotype , Proto-Oncogene Proteins c-fos/chemistry , Transcription Factors/chemistry , Vulva/cytology , Vulva/growth & developmentABSTRACT
The fusion of the Caenorhabditis elegans uterine anchor cell (AC) with the uterine-seam cell (utse) is an excellent model system for studying cell-cell fusion, which is essential to animal development. We obtained an egg-laying defective (Egl) mutant in which the AC fails to fuse with the utse. This defect is highly specific: other aspects of utse development and other cell fusions appear to occur normally. We find that defect is due to a missense mutation in the nsf-1 gene, which encodes N-ethylmaleimide-sensitive factor (NSF), an intracellular membrane fusion factor. There are two NSF-1 isoforms, which are expressed in distinct tissues through two separate promoters. NSF-1L is expressed in the uterus, including the AC. We find that nsf-1 is required cell-autonomously in the AC for its fusion with the utse. Our results establish AC fusion as a paradigm for studying cell fusion at single cell resolution and demonstrate that the NSF ATPase is a key player in this process.
Subject(s)
Caenorhabditis elegans Proteins/metabolism , Ethylmaleimide/pharmacology , N-Ethylmaleimide-Sensitive Proteins/drug effects , N-Ethylmaleimide-Sensitive Proteins/metabolism , Uterus/cytology , Animals , Animals, Genetically Modified , Caenorhabditis elegans/drug effects , Caenorhabditis elegans/physiology , Caenorhabditis elegans Proteins/drug effects , Caenorhabditis elegans Proteins/genetics , Cell Fusion , Female , Membrane Glycoproteins/drug effects , Membrane Glycoproteins/genetics , Membrane Glycoproteins/metabolism , Mutation, Missense , N-Ethylmaleimide-Sensitive Proteins/genetics , Organ Specificity , Phenotype , Promoter Regions, Genetic , Uterus/drug effectsABSTRACT
The development of multicellular organisms requires precise spatiotemporal gene expression and the expression of cell/tissue specific isoforms of some genes. This task may require more efficient genome organization in Caenorhabditis elegans and other organisms with relatively small genome size. The SL1 leader sequence is trans-spliced to many mRNAs in C. elegans. We hypothesize that introns coupled to internal SL1 acceptors contain independent promoters. We identify 238 genes that have introns coupled to internal SL1 acceptors. We find that the mean length of the internal SL1-coupled introns is significantly longer than the genome mean. For twelve of the genes, evidence exists that the intronic promoter provides tissue specificity different from that of the primary promoter. We estimate that 2.7% of the genome is regulated through this two-promoter system. We propose that internal SL1-coupled introns function as independent promoters and that this two-promoter system represents a major mechanism in C. elegans, in addition to alternative splicing, that serves to promote tissue-specific expression of protein isoforms. Our finding of the frequent coupling between an internal SL1 and a large immediately upstream intron will make promoters and transcription start sites predictable.
Subject(s)
Caenorhabditis elegans/genetics , Gene Expression Regulation, Developmental/physiology , Promoter Regions, Genetic , Animals , Caenorhabditis elegans/metabolism , Protein Isoforms/biosynthesis , Protein Isoforms/genetics , RNA, Spliced Leader/geneticsABSTRACT
We isolated egl-13 mutants in which the pi cells of the Caenorhabditis elegans uterus initially appeared to develop normally but then underwent an extra round of cell division. The data suggest that egl-13 is required for maintenance of the pi cell fate.
