Developmental Genetics Overview of gene structure Mechanisms of gene regulation Drosophila: Genetics model for Developmental

Biology

What is a gene?

CDSRegulatoryPromoter

Core Promote

r

-10-35 +1

3 UTR

AAAAAAAUG UAA

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?

Chromatin Remodeling

Histone Code: Modification of Histone tails. Acetylation, methylation, and

phosphorylation. Charged residues in tail.

Histone Methylation 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.

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.

Epigenetic Memory Trithorax- keeps genes active.

Counteract Polycombs Modify nucleosomes Keep H3K4 trimethylated

Polycomb- keeps genes inactivated. H3K27 methylase Bind meH3 tails

Methylation of DNA Once gene is turned on and needs to stay on CpG-usually associated with repression.

b-globin promoter. Methylation status of promoter can change

during development. Ex. Embryonic hemoglobin (e-globin) fetal

hemoglobin (g-globin)

Methylation and Transcriptional repression Can block

transcription factor binding

Recruit Histone methylases and acetylases Ex. MeCP2

Dnmt3 and Dnmt1 result in the heritability of methylated DNA regions in progeny cells.

Methylation can inactivate entire chromosomes.

Transcriptional regulation cis factors trans factors

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.

Promoter fusions Identifying new

enhancers Reporter genes: b-gal

and GFP

Enhancer Modulation Multiple transcription

factors can bind to a single Promoter region.

Pax6 enhancer region-differential transcription factor binding for different tissue types.

Pax61 Core promoter1 2 3 4

Pay it forward Pax6 is a

transcriptional regulator.

Pax6 works with Sox2 and L-Maf to regulate the crystallin gene.

Pax6 also regulates Pancreas related genes Insulin, glucagon, and

somatostatin Pax6 regulates itself!

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).

Transcription Factor Domains. DNA binding domain Transactivating

Domain Protein-Protein

Interaction domain.

MITF TranscriptionFactor- Ear developmentAnd Pigment production

“Pioneer” transcription factors. Pioneer transcription

factors can penetrate repressed chromatin.

FoxA1 Pax7 Pbx

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.

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.

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.

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.

miRNA miRNA ancient form

of regulation. Protection against

viral pathogens Quick regulation and

turnover of mRNA.

Drosophila Development: Genetics at work!

Development of Drosophila

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).

Anterior-Posterior Polarity

Dorsal-Ventral Patterning

Dorsal Gradient