Biol168_10F_Lecture 10_15Oct2010

Biol168_10F_Lecture - Dr Morris Maduro UC Riverside Biology 168 10F Lecture 10 page 1 Lecture#10 C elegans Endomesoderm Specification Textbook 2nd

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Dr. Morris Maduro, UC Riverside Biology 168 – 10F – Lecture 10, page 1 Lecture #10: C. elegans Endomesoderm Specification Textbook: 2nd edition: pp. 191-201; 3rd edition: 185-195. The Endomesoderm Gene Network The EMS cell generates mesoderm and endoderm ( = endomesoderm) and is specified by maternal SKN-1. SKN-1 is a transcription factor that specifies MS and E fates by activating downstream target genes. Two targets, MED-1 and MED-2 (me send oderm, a term similar to endomesoderm), are encoded by two nearly-identical genes found on different chromosomes. What is the evidence that these genes are the SKN-1 targets that specify MS and E fates? MED-1/2 Specify MS and E fates Time and place of MED-1/2. A reporter gene fusion containing the med-1 or med-2 promoter demonstrates expression in the MS and E cells. In skn-1 mutants, this expression disappears. If skn- 1 is expressed throughout the embryo using a heat-shock promoter::SKN-1 fusion, med-1 ::GFP is expressed throughout the embryo. Therefore, MED-1,2 are in the right place and time to specify MS and E, and SKN-1 is both necessary and sufficient to activate med-1,2 . Phenotype of med-1,2(-) . Using RNA interference (or double chromosomal mutants) to deplete med-1,2 , embryos do not develop properly and lack posterior pharynx most of the time, and intestine some of the time (cell types made by MS and E, respectively). Using a laser microbeam to kill all cells except MS or E, it is found that MS, and E (when it is not specified) each make body muscle and hypodermis in med-1,2(-) embryos. This phenotype is similar to skn-1 mutants and demonstrates that med-1,2 are necessary for MS specification, and participate in E specification. Overexpression of med-1 . Delivery of a short heat pulse to transgenic embryos carrying a heat- shock::MED-1 fusion results in the generation of arrested embryos containing excess pharynx and intestinal cells. This shows that med-1 is sufficient to specify MS- and E-like fates outside of the normal MS and E context. The med-1 promoter binds SKN-1. SKN-1 protein can directly bind the med-1 promoter as shown by a gel shift assay . MED-1 and MED-2 themselves are zinc finger transcription factors. Like SKN-1, their expression is also
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This note was uploaded on 10/28/2010 for the course BIOL 168 taught by Professor Maduro during the Spring '10 term at UC Riverside.

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Biol168_10F_Lecture - Dr Morris Maduro UC Riverside Biology 168 10F Lecture 10 page 1 Lecture#10 C elegans Endomesoderm Specification Textbook 2nd

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