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Developmental Genetics

Developmental Genetics. Overview of gene structure Mechanisms of gene regulation Drosophila: Genetics model for Developmental Biology. What is a gene?. -10. -35. +1. AAAAAA. UAA. AUG. Regulatory Promoter. 3 UTR. Core Promoter. CDS. Developmental Genetics.

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Developmental Genetics

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  1. Developmental Genetics • Overview of gene structure • Mechanisms of gene regulation • Drosophila: Genetics model for Developmental Biology

  2. What is a gene? -10 -35 +1 AAAAAA UAA AUG Regulatory Promoter 3 UTR Core Promoter CDS

  3. Developmental Genetics • Differentiation of cells requires regulation of specific genes. • Timing of Gene Regulation can determine when a tissue develops or when cells undergo Apoptosis. • How can we regulate gene expression?

  4. Chromatin Remodeling

  5. Histone Code: Modification of Histone tails. • Acetylation, methylation, and phosphorylation. • Charged residues in tail.

  6. HistoneMethylation • Methylation of residues on H3 tail • Methylation of H3K4(meH3K4) + high acetylation of H3/H4 tails)= active transcription. • meH3K9+low acetylation of H3/H4= highly repressed • meH3K9, meH3K27, meH4K20 =highly repressed.

  7. Example: Hox genes • Hox genes are responsible for determining the fate of segments along the anterior-posterior axis. • Trimethylation of H3K27 represses Hox genes. • Demethylase for me3H3K27 is recruited in differentiated cells to open up the promoters for Hox genes.

  8. Epigenetic Memory • Trithorax- keeps genes active. • Counteract Polycombs • Modify nucleosomes • Keep H3K4 trimethylated • Polycomb- keeps genes inactivated. • H3K27 methylase • Bind meH3 tails

  9. Methylation of DNA • Once gene is turned on and needs to stay on • CpG-usually associated with repression. • b-globinpromoter. • Methylation status of promoter can change during development. • Ex. Embryonic hemoglobin (e-globin) fetal hemoglobin (g-globin)

  10. Methylation and Transcriptional repression • Can block transcription factor binding • Recruit Histonemethylases and acetylases • Ex. MeCP2 • Dnmt3 and Dnmt1 result in the heritability of methylated DNA regions in progeny cells. • Methylation can inactivate entire chromosomes.

  11. Transcriptional regulation • cisfactors • trans factors

  12. Promoters/enhancers • Core promoter • RNA Pol II binds to this region. • Directly upstream of transcription start site. • Regulatory Promoter • Region upstream of core promoter • Contains enhancers/regulatory binding sites • Highly modular.

  13. Promoter fusions • Identifying new enhancers • Reporter genes: b-gal and GFP

  14. Enhancer Modulation • Multiple transcription factors can bind to a single Promoter region. • Pax6 enhancer region-differential transcription factor binding for different tissue types. 1 Core promoter Pax6 1 2 3 4

  15. Pay it forward • Pax6 is a transcriptional regulator. • Pax6 works with Sox2 and L-Maf to regulate the crystallingene. • Pax6 also regulates Pancreas related genes • Insulin, glucagon, and somatostatin • Pax6 regulates itself!

  16. Transcription Factors • Core Promoter • TFIID/TBP stabilized by TFIIA • TFIIH binds, RNA Pol II with TFIIE/TFIIF binds subsequently. • TFIIH phosphroylates RNA Pol II CTD. • Regulatory Promoter • Wide array of factors bind to enhancer regions. (Pax6 regulation).

  17. Transcription Factor Domains. • DNA binding domain • Transactivating Domain • Protein-Protein Interaction domain. MITF Transcription Factor- Ear development And Pigment production

  18. “Pioneer” transcription factors. • Pioneer transcription factors can penetrate repressed chromatin. • FoxA1 • Pax7 • Pbx

  19. Gene Silencing • Neural restrictive silencer element (NRSE) found represses neural genes in non-neural cells. NRSF binds to this element. • L1 is critical for brain development. • Transgene reporter with NRSE= neural tissue expression only • Transgene reporter without NRSE= all tissues.

  20. Regulation of mRNA • mRNA must undergo splicing for protein to be made. • Regulation of mRNA • Determination of which transcripts get translated • Splicing combinations to make new protein.

  21. Splicing: different gene products from one gene. • Bcl-x transcript. • Bcl-xL and Bcl-xS • Tropomysin • Leads to multiple proteins that differ in function and location. • Splicing enhancers-found in specific tissues. • Splicing can silence as well- splice excludes an exon from mRNA.

  22. Translational Regulation • Stored oocyte mRNAs- selective inhibition of translation. • Genes turned on quickly post-fertilization. • Relies on the recruitment of proteins involved in making a polyA tail. • Drosophila Bicoid gene product.

  23. miRNA • miRNA ancient form of regulation. • Protection against viral pathogens • Quick regulation and turnover of mRNA.

  24. Drosophila Development: Genetics at work!

  25. Development of Drosophila

  26. Anterior-Posterior Polarity • Starts during oogenesis • Gurken mRNA transferred to oocyte. • Signal sent back to oocyte post Gurken/Torpedo interaction. • Par-1 mediated organization of microtubules to posterior side of oocyte. Minus end (posterior) and plus end (anterior).

  27. Anterior-Posterior Polarity

  28. Dorsal-Ventral Patterning

  29. Dorsal Gradient

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