Lecture 20 continued: Drosophila embryogenesisEmbrygenesisFour classes of genes:Maternal genesGap genesPair-rule genesSegment polarity genesHomeotic genesRead 826-837Fig. D18-D27; 19.2; 19.16“Molecular Biology of the Cell” ed. ByBruce Albert et al. (free onlinethrough ncbi books)Fig. D.24Segment polarity genesFig. D.25Segment polarity genes are lowest level ofsegmentation hierarchy• Mutations in segment polarity genes causedeletion of part of each segment and itsreplacement by mirror image of different partof next segment• Regulatory system complex– Transcription factors encoded by pair-rule genesinitiate pattern by regulating segment polarity genes– Interactions between cell polarity genes maintainperiodicity later in developmentSegment polarity genes are lowest level ofsegmentation hierarchy• Mutations in segment polarity genes causedeletion of part of each segment and itsreplacement by mirror image of different partof next segment• Regulatory system complex– Transcription factors encoded by pair-rule genesinitiate pattern by regulating segment polarity genes– Interactions between cell polarity genes maintainperiodicity later in developmentEach segment establishes own identity throughactivation of homeotic genes• Homeotic mutations causedifferent segments todevelop as if locatedelsewhere•bithorax (bx)– Anterior third thoracicsegment (T3) develops likesecond anterior thoracicsegment (T2)–postbithorax (pbx)posterior T3 transformsinto posterior T2Fig. D.26Antennapedia Complex and Bithorax Complex• Homeotic selector genes– Two clusters of genes onthird chromosome –antennapedia complex andbithorax complex– Responsible fordetermining segmentidentity- All encode HomeoboxFig. D.27Figure 21-43. The patterns ofexpression compared to thechromosomal locations of thegenes of the Hox complex. Thesequence of genes in each of thetwo subdivisions of thechromosomal complexcorresponds to the spatialsequence in which the genes areexpressed. Note that most of thegenes are expressed at a highlevel throughout oneparasegment (dark color) and ata lower level in some adjacentparasegments (medium colorwhere the presence of thetranscripts is necessary for anormal phenotype, light colorwhere it is not). In regions wherethe expression domains overlap,it is usually the most “posterior”of the locally active genes thatdetermines the local phenotype.(From Bruce Albert Book)Fig. 19.16HomeodomainLecture 21 Mouse (Mus musculus)A Model for studying human diseasesRead 845-862Fig. E3, 5, 6, 8, 9, 10, 11, 14, 15, 16, 17Table E.1Fig. E.3SyntenyBetween mouse and human genomeFig. E.5Mouse embryogenesisFig. E.6ChimeraCleavage stage cells are totipotentKnocking out a gene in ES cellsUsing transgenic tools(1) verify gene cloningFig. E.9Using transgenic technology(2) characterize regulatory regions• DNA constructcontaining mouseregulatory region ofinterest is attached to E.coli reporter gene.• Function ascertained byβ-gal expression intransgene fetusFig. E..11Using transgenic technology(3) mis-express genes• Transgenicexpression of mycgene providesinformation ongene’s role intumor formationFig. E.10Fig. E.14a-cUsing transgenic technology(4) Gene knockouts to create mouse model for human diseasesFig. E.14d-eFig. E.14fFig.
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