How can organisms generate so many structurally and functionally different cells?

Differential Gene Expression Genome is same, but the shapes and functions of cells are different How are there so many different cells developed from one cell (fertilized egg)? Condition 1.DNA of all differentiated cells are identical. 2.Unexpressed genes in the differentiated cells are not mutated. *evidence) animal cloning is successful even with adult cells 3. Only small percentage of the genome is expressed in each cell.

Figure 2.1 Cloned mammals have been created using nuclei from adult somatic cells Q) Why was the rate of somatic cloning so extremely lower ?

Figure 2.2 The kitten “CC” The same genotypes give rise to multiple phenotypes. The same genes do not determine every detail of physiques and personalities ? X-chromosomal inactivation? DNA methylation (modification)

The Paradigm of Differential Gene Expression Differential gene expression from the same gene repertoire. 1.Differential gene transcription 2.Selective nuclear RNA processing 3.Selective mRNA translation 4.Differential protein modification

Figure 2.3 Nucleosome and chromatin structure (Part 1)

Figure 2.3 Nucleosome and chromatin structure (Part 2)

Figure 2.3 Nucleosome and chromatin structure (Part 3)

Figure 2.4 Histone methylations on histone H3 Repression

Figure 2.5 Nucleotide sequence of the human β-globin gene (Part 1)

Figure 2.5 Nucleotide sequence of the human β-globin gene (Part 2)

Figure 2.6 Summary of steps involved in the production of β-globin and hemoglobin (Part 1)

Figure 2.6 Summary of steps involved in the production of β-globin and hemoglobin (Part 2)

Figure 2.7 Formation of the active eukaryotic transcription pre-initiation complex

Figure 2.8 The genetic elements regulating tissue-specific transcription can be identified by fusing reporter genes to suspected enhancer regions of the genes expressed in particular cell types Myf5-lacZ Crystallin-GFP

Figure 2.9 Enhancer region modularity Pax6 gene 1.Multiple transcription initiation sites: P0 and P1 2.Multiple enhancer elements: five enhancer elements known so far only for expression in the eye

Importance of enhancer elements for the differential gene expression 1.Most genes require enhancers for their expression 2.Enhancers are the major determinant of differential gene expression 3.One gene can have multiple enhancer elements 4.Multiple transcription factors can bind together on one enhancer element 5.Interaction between transcription factors on the enhancer and transcription initiation complex at the promoter 6.Mix and match of transcription factors for the differential gene expression (Combinatorial gene regulation) 7.Enhancers are modulator of gene expression: the strength of enhancer 8.Enhancers remodel chromatin to activate promoter or facilitate the binding of RNA polymerase to the promoter 9.Enhancer also can repress gene expression

Figure 2.11 RNA polymerase is stabilized on the promoter site of the DNA by transcription factors recruited by the enhancers

3-dimensional regulation of gene expression

Figure 2.10 Modular transcriptional regulatory regions using Pax6 as an activator

Figure 2.12 Stereoscopic model of Pax6 protein binding to its enhancer element in DNA

Figure 2.14 Three-dimensional model of the homodimeric transcription factor MITF (one protein in red, the other in blue) binding to a promoter element in DNA (white)

Figure 2.13 Pancreatic lineage and transcription factors Insulin GFP: Ngn3,Pdx1, Mafa co-expression in exocrine cells- begin to express insulin

Figure 2.15 Model for the role of the “pioneer” transcription factor Pbx in aligning the muscle- specific transcription factor MyoD on DNA

Other regulator of gene expression Silencer: repress gene expression (negative enhancer) Ex) Neural restrictive silencer element (NRSE), which is recognized by NRSF, repress gene expression except in neural tissues Insulator: provides barrier for enhancer’s action Figure 2.16 Silencers. Analysis of β-galactosidase staining patterns in 11.5-day embryonic mice

Figure 2.17 Methylation of globin genes in human embryonic blood cells

Figure 2.18 DNA methylation can block transcription by preventing transcription factors from binding to the enhancer region

Figure 2.19 Modifying nucleosomes through methylated DNA

Figure 2.20 Two DNA methyltransferases are critically important in modifying DNA

X chromosome inactivation in mammals (Part 1) Uneven coat color pattern: an evidence for the random X inactivation

Dosage compensation of X chromosome Drosophila Male: XO Female: XX Dosage compensation by acetylation-induced gene activation in male X chromosome Mammals Dosage compensation by converting X-chromosome in female into heterochromatin (Bar body) Evidenced by mouse coat color selection: no intermediate color Reactivation after entering meiosis of germ cells by erasing DNA methylation

Figure 2.21 X chromosome inactivation in mammals X-chromosome from male have LacZ transgene In mouse (not human) Paternal X- chromosome is preferentially inactivated in Trophoblast

Figure 2.22 Regulation of the imprinted Igf2 gene in the mouse

Genomic Imprinting Gamete-of-origin dependent modification of phenotype. The phenotype elicited from a locus is differentially modified by the sex of the parent contributing that particular allele. Mediated by allele-specific DNA methylation ~ 200 human genes are expected to be imprinted

Figure 2.23 Inheritance patterns for Prader-Willi and Angelman syndromes Prader-Willi syndrome: Mild mental retardation, obesity, small gonards, short stature Angelman sysdrome: sever mental retardation, seizure, lack of speech, 키득키득 ????( inappropriate laughter)

Roles of differential RNA processing during development

Figure 2.26 Some examples of alternative RNA splicing Prevent cell death Induce cell death

Figure 2.28 The Dscam gene of Drosophila can produce 38,016 different types of proteins by alternative nRNA splicing

Figure 2.29 Dscam protein is specifically required to keep dendrites from the same neuron from adhering to each other (Part 1)

Figure 2.29 Dscam protein is specifically required to keep dendrites from the same neuron from adhering to each other (Part 2)

Figure 2.30 Muscle hypertrophy through mispliced myostatin RNA Myostatin: A negative regulator of muscle precusor cell proliferation

Localization of Vg1 mRNA to the vegetal portion of the Xenopus oocyte

Control of Gene Expression at the Level of Translation mRNA longevity -Primarily depends on the poly(A) tails -Influenced by external factors (ex. Casein mRNA stays longer during lactation periods) Selective inhibition of mRNA translation -Regulatory sequences: 5’ cap and 3’ UTR -microRNA

Figure 2.31 Degradation of casein mRNA in the presence and absence of prolactin

Figure 2.32 Translational regulation in oocytes

Figure 2.33 Protein binding in Drosophila oocytes

Figure 2.34 Hypothetical model of the regulation of lin-14 mRNA translation by lin-4 RNAs

Figure 2.35 Current model for the formation and use of microRNAs

Figure 2.36 The lymphoid precursor cell can generate B cells or T cells

Figure 2.37 The miRNA complex, including numerous proteins that bind to the miRNA (miRNP), can block translation in several ways

Figure 2.38 Localization of mRNAs (Part 1)

Figure 2.38 Localization of mRNAs (Part 2)

Figure 2.38 Localization of mRNAs (Part 3)

Figure 2.39 A brain-specific RNA in a cultured mammalian neuron