2LSCI 1002_Lecture note_Differentiation_Cell Communications_Faye SY Tsang.pdf

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Faye Suk-Ying TSANG ( 曾淑瑩 ), PhD School of Life Sciences CUHK LSCI 1002 Introduction to Biological Sciences 生物科學入門 生物科學入門
Differentiation & Development
Basics of Developmental Biology Fertilization barb2right Formation of zygote barb2right Cleavage of zygote barb2right Formation of blastocyst which consists of inner cell mass (ICM), trophoblast & blastocystic cavity
boxshadowdwn Figure 2.23 (2n) (n)
Trophoblast Degenerating zona pellucida Inner cell mass Blastocystic cavity
Further Development Epiblast of the ICM barb2right 3 germ layers (ectoderm, endoderm, mesoderm) barb2right lineage commitment (progenitor cells barb2right differentiated cells)
ICM Epiblast Hypoblast Ectoderm of amnion Embryonic ectoderm Primitive streak Extraembryonic mesoderm Embryonic mesoderm Notochordal process Embryonic endoderm Endoderm of yolk sac Extraembryonic mesoderm
Regulation of Gene Expression boxshadowdwn In multicellular eukaryotes, gene expression regulates development & is responsible for differences in cell types
boxshadowdwn All organisms must regulate which genes are expressed at any given time boxshadowdwn Genes are turned on & off in response to signals from their external & internal environments boxshadowdwn In multicellular organisms, regulation of gene expression is essential for cell differentiation Differential Gene Expression
boxshadowdwn Almost all the cells in an organism contain an identical genome; differences between cell types result from differential gene expression , the expression of different genes by cells with the same genome Differential Gene Expression
boxshadowdwn During cellular differentiation: totipotent barb2right pluripotent barb2right multipotent barb2right differentiated cells. A single fertilized egg is eventually differentiated into different cell types by activating some genes while inhibiting other genes (differentiation is accompanied by dramatic changes in the numbers & types of transcripts expressed) Differential Gene Expression
Signal Chromatin Chromatin modification: DNA unpacking DNA Gene available for transcription RNA Cap NUCLEUS CYTOPLASM Degradation of mRNA RNA processing Tail mRNA in nucleus Transport to cytoplasm Transcription Exon Primary transcript Intron mRNA in cytoplasm Translation Polypeptide Protein processing Active protein Transport to cellular destination Cellular function (such as enzymatic activity or structural support) Degradation of protein Eukaryotic gene expression is regulated at many stages Fig 18.6 from Campbell
boxshadowdwn The structural organization of chromatin helps regulate gene expression in several ways boxshadowdwn Genes within highly packed heterochromatin are usually not expressed boxshadowdwn Chemical modifications to histones & DNA of chromatin influence chromatin structure & gene expression Regulation of Chromatin Structure
boxshadowdwn In histone acetylation , acetyl groups are attached to an amino acid in a histone tail boxshadowdwn This appears to open up the chromatin structure, thereby promoting the initiation of transcription

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