Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
The Developmental Fate of Cells Marissa and Katie Vocab • Induction-The process in which one group of embryonic cells influences the development of another, usually by causing changes in gene expression. • Fate Maps-A territorial diagram of embryonic development that displays the future derivatives of individual cells and tissues. • Totipotent-Describing a cell that can give rise to all parts of the embryo and adult, as well as extraembryonic membranes in species that have them. • Pattern Formation-The development of a multicellular organism’s spatial organization, the arrangement of organs and tissues in their characteristic places in threedimensional space. • Apical Ectodermal Ridge (AER)-A thickened area of ectoderm at the tip of a limb bud that promotes outgrowth of the limb bud. • Zone of Polarizing Activity (ZPA)-A block of mesoderm located just under the ectoderm where the posterior side of a limb bud is attached to the body; required for proper pattern formation along the anterior-posterior axis of the limb. • Positoinal Infortmation-Molecular cues that control pattern formation in an animal or plant embryonic structure by indicating a cell’s location relative to the organism’s body axes. These cues elicit a response by genes that regulate development. Introduction • The fate of cells is determined by signals and surroundings and influenced by other cells. 2 Ways to Alter Gene Expression 1. During early cleavage divisions, embryonic cells must somehow become different – Asymmetric Divisions 2. Once initial cell asymmetries are set up, subsequent interactions among the embryonic cells influence their fate – Induction Fate Maps • 1920s Walther Vogt charted maps of early Amphibian embryos and found that germ layers created by gastrulation were traced to the bastula, even before gastrulation • Caenorhabditis Elegans(worm) – Sydney Brenner, Robert Horvitz, and Jonathan Sulston determined complete lineage. – Figure 47.22 Changing Fate 1. Specific tissues of the older embryo are the products of a certain “founder cell” that contain unique factors as result of asymmetrical divisons. 2. As development proceeds a cell’s developmental potential becomes restricted. Establishing Axis • In amniotes and Mammals axis are established after cleavage • In nonamniotes axis are established during oogenesis • Figure 47.23 Totipotentcy • In mammals, Totipotent until 16-cell stage • In others, only totipotent when cytoplasmic determinants are present • Totipotency is lost as time goes on! “Organizer” • 1920s Hans Spemann and Hidle Mangold – Dorsal lip of blastopore in early gastrula in the organizer – It initiates a chain of interactions that result in formation of notochord, neural tube, and other organs. • Figure 47.24 BMP-4 • BMP-4 (bone morphogenetic protein 4) is a growth factor. • When it is in high concentration it signals cells on ventral side of gastrula to travel down a pathway to form ventral structure • The “organizer” inactivates BMP-4 on dorsal side with binding proteins promoting dorsal structures. Fate of Cells • Inductive signals play a major role in pattern formation • Positional cues tell a cell where it is in respect to the animals body. • Axes: – Anterior-Posterior – Ventral-Dorsol – Proximal-Distal Limb Bud Organizers • Two types 1. Apical Ectodermal Ridge (AER) 2. Zone of Polarizing Activity (ZPA) • Both can interact with each other to determine development. Apical Ectodermal Ridge (AER) • Removing AER blocks outgrowth of limbs along the Proximal-Distal Axis • Cells promote protein signals in fibroblast growth factor (FGF) that promote outgrowth Zone of Polarizing Activity (ZPA) • Block of mesodermal tissue • Located underneath the ectoderm where posterior side of bud is attached to body • Necessary for proper pattern formation along the anterior-posterior axis • Cells nearest ZPA = posterior structures • Cells farthest from ZPA = anterior structures