1. The Developmental Fate of Cells Marissa and Katie

2. 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 three- dimensional space.

3. 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.

4. Introduction The fate of cells is determined by signals and surroundings and influenced by other cells.

5. 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

6. 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

7. 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.

8. Establishing Axis In amniotes and Mammals axis are established after cleavage In nonamniotes axis are established during oogenesis Figure 47.23

9. Totipotentcy In mammals, Totipotent until 16-cell stage In others, only totipotent when cytoplasmic determinants are present Totipotency is lost as time goes on!

10. “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

11. 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.

12. 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

13. 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.

14. 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

15. 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