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UNT BIOL 4330 - Developmental Genetics

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BIOL 4330 1st Edition Lecture 2 Outline of Previous Lecture I. Intro to Developmental BiologyII. Approaches to Developmental BiologyIII. MorphogenesisIV. Selectable VariationOutline of Current Lecture I. Developmental GeneticsII. Gene Regulation in DevelopmentIII. Differential Gene Expressiona. Methylationb. nRNA Splicingc. RNA ProcessingCurrent LectureDevelopmental Genetics is the discipline that examines how the genotype is transformed into the phenotype.• Many conserved core processes that are responsible for generating most of the anatomy, physiology and behavior of an organism.• All evolved between 3 billion and half billion years ago• Includes metabolism, gene expression and signaling between cells. Conservation and Economy• Complexity of an organism must arise through the multiple use of a few conserved elements. • Core processes are linked to one another• Linkage –regulatory linkage means how information is passed from one component to another (how one molecule passes information to another)These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.The Monod Experiment: discovered the process of gene expression- a core process for generating phenotypic variation.Understanding embryonic development is central for explaining phenotypic novelty in animals.Gene Regulation in Development• Understanding embryonic development is central for explaining phenotypic novelty in animals• Most of the phenotypic and physiological complexity is established in the embryo• Every new gene in evolution must somehow be linked to a transcriptional regulatory program, and old genes continue to undergo changes of regulation.Genomic Equivalence : each somatic cell nucleus has the same set of Xsomes and genes (or genome). Evidence for these includes cloning a mammal using nuclei from adult somatic cells.Differential Gene Expression: Three Postulates1) Every cell nucleus contains the complete genome established in the fertilized egg. In molecular terms, the DNAs of all differentiated cells are identical2) The unused genes in differentiated cells are either destroyed nor mutated, but retain thepotential for being expressed3) Only a small percentage of the genome is expressed in each cell, and a portion of the RNA synthetized in each cell is specific for that cell type Gene expression can be regulated at several levels:1) Differential gene transcription- regulates which of the nuclear genes are transcribed intonuclear RNA2) Selective nuclear RNA processing- regulates which of the transcribed RNAs (or nuclear RNAs) are able to enter into the cytoplasm and become mRNAs3) Selective messenger RNA translation – regulates which of the mRNAs in the cytoplasm are translated into proteins4) Differential protein modification- regulates which proteins are allowed to remain and/or function in the cell Enhancers are DNA sequences that control the efficiency and rate of transcription from a specific promoter.1. Most genes require enhancers for their transcription2. Enhancers are the major determinant of differential transcription in space (cell type) and time.3. Enhancers can function far from the promoter and each enhancer can be bound by more than one transcription factor4. Interaction between TFs bound to enhancer sites and transcription initiation complex assembled at the promoter is thought to regulate transcription5. Enhancers are combinatorial; various DNA sequences regulate temporal and spatial gene expression and these can be mixed and matched.6. Enhancers are modular. A gene can have several enhancer elements, each of which turns it on a different set of cells.7. Enhancers generally activate transcription by one of two means: they either remodel chromatin to expose the promoter, or they facilitate the binding of RNA polymerase to the promoter by stabilizing TAFs8. Enhancers also inhibit transcription…these are called silencers. The bridge between enhancer and promoter can be made by transcription factors.The genetic elements regulating tissue-specific transcription can be identified by fusing reportergenes to suspected enhancer regions of the genes expressed in particular cell typesThe gene for GFP is fused to a lens crystallin enhancer gene in Xenopus and the result is the expression of GFP in the tadpole lens. Enhancer region of the muscle-specific protein Myf-5 protein is fused to β-galac. Reporter gene and injected into the mouse embryo-lights up darkly stained muscle areas.The genetic elements regulating tissue-specific transcription can be identified by fusing reportergenes to suspected enhancer regions of the genes expressed in particular cell types.Combinatorial Association• Genes for specific proteins use numerous TFs in various combinations• Enhancers are modular (e.g. Pax6 gene is expressed in the eye, pancreas & nervous system)• Within a cis-regulatory module TFs work a in combinatorial way (Pax6, L-Maf & Sox2 are needed for the transcription in of crystallin in the lens)• Combinatorial association of TFs on enhancers leads to the spatiotemporal output of anygeneTranscription Factors (TFs)• TFs are proteins that bind to enhancer or promoter regions and interact to activate or repress the transcription of a particular gene. • Most TFs can bind to specific DNA sequences• TFs can be grouped together in families based on similarities in structure. Three major TF Domains:• DNA binding domain-recognizes specific DNA sequences• Trans-activating domain-activates or suppresses the transcription of the gene whose promoter or enhancer it has bound.• Protein-protein interaction domain-allows the TF’s activity to be modulated by TAFs (transcription associated factors) or other TFs. Microphthalmia (MITF) is a TF that is active in the ear and in the pigment forming cells of the eye and skin- has a protein-protein interaction domain enabling dimerization with another MITFproteins. The homodimer is a functional protein that can bind to DNA and activate transcription of certain genes. Absence of MITF leads to no melanin pigment, deafness, multicolored irises.Differential methylation • Differential methylation is one of the most important mechanisms of epigenetic changes• An organism cannot be explained only by its genes• We need to know the developmental patterns as well as genetic ones Differential nRNA splicing• Alternative nRNA splicing is a


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