Chapter 211. Shared Development Processesa. a few fundamental principles are common-to all developmental seqs observed in multi-cellular organisms2. Cell Proliferationa. Dividing of cells to make more cellsb. location, timing, extent of cell division have to be tightly controlledc. There undifferentiated cells that keep proliferating throughout an organism's life-in plants these cells are grouped into meristems-which give rise to structures that develop throughout life (stems, leaves, etc.)d. In animals these cells are called stem cells-embryonic cells have give rise to any cell type in the body-in adults they are found in areas where constant cell division is necessary3. Programmed Cell Death-Apoptosisa. Occurs as certain tissue take shape-cells bet. toes of chicken must die in order for separate toes to formb. Ellis and Horvitz investigated cells that cause apoptosis compared to those that dont-uncovered 2 genes essential for apoptosisc. When genes causing apoptosis in mice were disrupted-result was a malformation of the braind. Normal apoptosis is imp. in development of human embryose. inappropriate activation of programmed cell death-involved in neurodegenerative diseasees such as Lou Gehrigs Disease4. Cell Movement or Cell Growtha. Many cells have to move to a new location-in order for normal development to occurb. During gastrulation cells in diff. parts of the mass rearrange themselves into 3 layers-which give rise to skin, gut, and other parts of the body-all of this comes from mass of similar looking cells that develop early in developmentc. certain animal cells break away and move to new location-where they give rise to other kinds of cellsd. Plant cells are encased in stiff cell walls and dont move-changes in direction of cell growth result in proper formation-of straight and bent stems, leaf veins, and other structurese. differential cell growth-key part of plant development5. Cell Differentiationa. process of becoming a specialized type of cellb. initially, cells can differentiate into any cell type-but most commit to certain function early in developmentc. Some plant cells can change structure and function-cells like these are called totipotent cellsd. Totipotent cells highlight key diff. bet. animal and plant cells6. Cell-Cell Interactionsa. During development most important cell-cell interactions-involve sending and receiving signalsb. embryonic cells grow, move, differentiate-in response to signals from other cellsc. Signal Transduction Pathways trigger production-of the transcription factorsd. cell-cell signals can change patterns of gene expression and thus the embryonic cells structure and behaviorRole of Differential Gene Expression In Development1. Differentiated Plant Cells Are Genetically Equivalenta. Proof: cells from stem of cedar tree can de-differentiate to form roots-cells must contain genes for root cells as wellb. All plant cells contain the same genec. Processes that control gene expression-such as chromatin structure, Regulatory transcription factors, RNA processing -miRNA activity, etc get reprogrammed in de-differentiation2. Differentiated Animal Cells Are Genetically Equivalent Draw figure 21.2a. Ian Wilmut and colleagues reported results of nuclear transfer experimentb. removed mammary gland cells from pregnant female sheep-grew them in culture and fused them w eggs-whose nuclei had been removed-resulting embryos were placed in uteri of surrogate mothers-in one of the transfer attemps Dolly a clone was bornc. majority of nuclear transplant experiments faild. This has proven that differentiation doesnt involve change in genetic make up of cell-but rather results from differential gene expression3. How Differential Gene Expression Occursa. Transcriptional responsible for gene differentiation-only mRNA genes needed for a muscle cell will be produced for a muscle cellb. In eukaryotes transcription controlled by presence of regulatory transcription factors1. Cell-Cell Signals Trigger Differential Gene Expressiona. whether a cell becomes certain kind of cell (muscle, nerve, etc)-depends on location along 4 axes: Organism's stage of development-and 3 spatial dimensions Draw1. One axis runs anterior (twd the head) to posterior (twd the tail)2. One axis runs ventral (twd the belly) to dorsal (twd the back)3. One axis runs left to right2. Master Regulators Set up the Major Body Axesa. Pattern Formation describes events that determine spatial organization of an embryob. Early signals act as master regulators that set up the axes (Master Regulators)c. As growth continues, new signals arrive and activate genes-that specify finer control over what a cell becomes3. Discovery of BICOIDa. Experiment with fruit flies and mutants-one mujtation caused embryos missing structures found in anterior end-instead anterior end contained structures normally found in the posteriorb. gene responsible for this phenotype called Bicoid gene which must provide positional info.c. bicoid gene coded for signal that tells cells where they are located-along the anterior-posterior body axis4. The Importance of Concentration Gradientsa. Nusslein-Volhard used Situ Hybridization Draw from figure 21.5-to find where bicoid mRNAs are located in embryosb. probes were designed to bind to bicoid mRNA inside the embryoc. mRNA for bicoid was found to be highly localized in anterior endd. protein product forms steep concentration gradient-bicoid protein abundant in anterior-medium amount means in between poster and anterior-low amount means in posterior5. Auxin's Role in Plant Developmenta. Bicoid called a master regulatorb. plants also have master regulator that is a hormone-cell-cell signal in plants called auxin enters cells and triggers-the production of transcription factors that affect differentiationc. Auxin produced in meristematic cells at the tip or apex of embryod. If high concentration of auxin in root-it means the cell is in the root and etc.e. molecules that provide spatial information during embryonic development-via concentration gradient are called morphagens-both bicoid and auxin are morphagens6. Regulatory Genes Provide Specific Positional Informationa. Differentiation is a progressive step by step processb Segment-a region of organism that contains a distinct set of structures-and is repeated along its lengthc. Defects in how body segments are organized-attributed to defective segmentation genesd. 3 Classes of segmentation genes Draw1. gap genes expressed first in
View Full Document
Unlocking...