Activation of the mec-3 promoter in two classes of stereotyped lineages in Caenorhabditis elegans.
The mec-3 gene of Caenorhabditis elegans encodes a homeodomain protein and is expressed in one of two cells upon asymmetric cell division. As a result of asymmetric mec-3 expression, the two sister cells express different fates, so mec-3 is a likely target for the machinery that mediates asymmetric cell division. The unc-86 gene encodes a homeodomain protein of the POU family, which activates mec-3 by binding to its promoter. The ten mec-3-expressing cells are a subset of the anterior daughters of UNC-86-containing cells. Posterior daughters of UNC-86-containing cells do not express mec-3, even though the UNC-86 protein is distributed into both daughter cells. Lineages that express the unc-86 and mec-3 genes can be grouped into two types: in Type I lineages, UNC-86 protein is first made in the immediate parent of the terminal mec-3-expressing cell, while in Type II lineages, UNC-86 is first made in the grandparent of the terminal mec-3-expressing cell. The purpose of experiments presented here is to understand the relationship between the mec-3 expression patterns in each type of lineage, and to determine the fundamental activity pattern of the mec-3 promoter. We find that in the Type I V5.pa lineage, mec-3-lacZ is first synthesized in the terminal PVDR neuron, one cell division after unc-86 is expressed. mec-3 expression in PVDR can occur by transcriptional regulation alone; segregation of the mec-3 RNA or protein is not required to explain the asymmetric expression of mec-3. In the Type II Q lineage, the mec-3 promoter activity can be detected in the immediate anterior daughter of the first unc-86-expressing cell, but when this cell divides, mec-3 is expressed in only one of its daughters at later times. It seems likely that, in the short-lived immediate anterior daughter cell in Type II lineages, mec-3 product does not accumulate to levels that can influence subsequent events. Our results suggest that the mec-3 promoter is activated in all anterior daughters of unc-86-expressing cells.
Wang
L
L
Department of Biology, Nelson Laboratories, Rutgers University, Piscataway, NJ 08855, USA.
Way
J C
JC
D000818:Animals; D030801:Animals, Genetically Modified; D017209:Apoptosis / Q000235:genetics; D017173:Caenorhabditis elegans / Q000196:embryology / Q000235:genetics*; D029742:Caenorhabditis elegans Proteins; D002455:Cell Division; D019070:Cell Lineage; D016764:Cell Polarity / Q000235:genetics*; D004625:Embryo, Nonmammalian / Q000166:cytology / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D006360:Heat-Shock Proteins / Q000235:genetics; D015801:Helminth Proteins / Q000096:biosynthesis / Q000235:genetics*; D018398:Homeodomain Proteins / Q000502:physiology; D060850:LIM-Homeodomain Proteins; D009419:Nerve Tissue Proteins / Q000096:biosynthesis / Q000235:genetics*; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D050809:POU Domain Factors; D011401:Promoter Regions, Genetic; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors / Q000502:physiology
D029742:Caenorhabditis elegans Proteins; D006360:Heat-Shock Proteins; D015801:Helminth Proteins; D018398:Homeodomain Proteins; D060850:LIM-Homeodomain Proteins; D009419:Nerve Tissue Proteins; D050809:POU Domain Factors; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; C072005:mec-3 protein, C elegans; C081539:unc-86 protein, C elegans