CHAPTER 22 Principles of Development PPT Notes 4 25 2014 o o o o o fundamental principles common to all developmental sequences observed in multicellular organisms lead to individual organisms development o 1 cell division proliferation cells divide by mitosis cytokinesis w regulated timing location amt of cell division controlled by interacting layers of regulation necessary for individual to develop from undifferentiated mass of cells most cells stop proliferating at maturity meristems plants stem cells animals specialized undifferentiated cells that continue proliferating throughout organism s life 2 cell cell interactions signals made by cells influence neighbor cells to divide die move differentiate patterns of gene expression are essential for cell activity during development during development most impt interactions involve sending receiving signals 3 cell differentiation undifferentiated cells specialize specific times places in stepwise fashion differentiation step by step process where cells are committed to a specific developmental pathway and later become differentiated to become specialized plant cells capable of de differentiating after specialization bc plant meristems animal stem cell remain undifferentiated o o in animals stem cells can divide make specialized cell types in plants meristems can make structures that develop throughout life plant cells can de differentiate to form other plant parts each cell has to have genes needed by all different types of plant cells in animals cells move past one another shape in embryo cells break away migrate to new locations in plants cells regulate plane of cell division expand in specific directions shape gastrulation cells in different parts of early embryo rearrange into 3 distinctive types of embryonic tissue that later form specific organs plant cells cannot move bc of cell walls but s in orientation of cell division control direction of o 4 cell movement expansion o 5 programmed cell death apoptosis cell proliferation expansion regulated timing location amt of cell death abnormal apoptosis can lead to disease deformation differential gene expression expression of different genes in different cell types key to cell differentiation during development research shows that cellular differentiate does not involve changes in genetic makeup of cells but results from differential gene expression gene can be regulated levels of transcription RNA processing translation and post translation translation fundamental lvl of control in differential gene expression during development in eukaryotes controlled by regulatory transcription factors proteins triggered by chemical signals that tell cells where they are in time space activates transcription factors that turn genes on off cause differentiation fate of cell depends on timing stage of development of organism spatial location within body of organism spatial location determined by 3 major body axes in early development o o o anterior posterior ventral dorsal left right pattern formation series of events that determine spatial organization of embryo o mutant embryos helped identify more than 100 genes that play fundamental roles in pattern formation thanks to experiments by Nusslein Volhard Wieschaus on fruit flies 4 25 2014 bicoid 2 tailed protein gene replaced anterior structures w posterior provides positional information in coded signal acts as master regulator in embryos o location in anterior of the egg found via in situ hybridization label probe add to specimen remove excess probe observe location of probe protein made from mRNA in anterior end and diffuses away from that end of embryo o o makes a steep concentration gradient from anterior to posterior end gives cells info w protein abt spatial position turns on genes responsible for forming anterior structures its absence contributes to formation of posterior structures high levels of bicoid transcription of genes that make anterior structures low levels opposite morphogens signals that set up major body axes of embryo activate network of genes that send signals w more specific information abt spatial location of cells trigger production of other egualtory signals transcription factors trigger production of another set of signals regulatory proteins etc as development occurs signals activate genes that specify finer control over what a cell becomes o o o animal cloning experiments transplanting nuclei from diploid frog cells into unfertilized cells w o nuclei made normal tadpoles o o mammary gland cells from adult sheep fused w enucleated eggs implanted into surrogate mother fertile genetically identical clone sheep born Dolly segmentation genes regulatory genes that give increasingly specific positional formation expressed in sequence and in increasingly restricted regions o o o segment region of animal body that has distinct set of structures is repeated along length organize cells tissues into distinct segments 3 classes identified in fruit fly gap genes define general position of segments in anterior middle posterior of body function early in development pair rule genes demarcate boundaries of individual segments function later in development segment polarity genes delineate boundaries in individual segments function later in development hox genes activates after segmentation genes products identify each segment s structural role genes trigger development of structures that are appropriate to each type of segment o specify which body structures to build mutations defects in pattern formation expressed in pattern along anterior posterior axis after segments established code for regulatory transcription factors that trigger the production of segment specific structures clusters occur in every animal examined to date vary similar chromosomal organization at least some molecular mechanisms of pattern formation conserved during animal evolution underlying mechanisms responsible for development similar in animal bodies genes in Hox complexes of animals are homologous regulatory cascade formed from interaction among bicoid segmentation genes bicoid gene gap genes pair rule genes segment polarity genes homeotic hox genes define a level in the cascade regulatory genes overall function act in a sequence trigger gene cascades that provide progressively detailed information about where cells are located in time space cells receive unique positional information bc identity concentration of signals transcription factors vary along
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