Developmental Biology

Katherine Alvarado

Developmental Biology

Fall 2014

Exam 2

1. Define, compare and contrast and vegetal pole of the early embryo.

2. Gradients of paracrine factors can setup a field in which a field of cells (tissue) is exposed to different concentrations of the paracrine factor. Describe an in vitro experiment which demonstrated that morphogenic fields can explain variable differentiation and variable fate of cells within the same fields. Name the source of the cells, the tissue, and all of the specifics with regards to differentiation and markers signaling factors including experimental designs and the concentrations of signaling factors involved. Also, explain how a gradient was established in vitro.

3. Describe an in vitro experiment which demonstrates how morphogenic fields work. Name the organisms, the stage of development.

4. Explain the role of bicoid and nanos in Drosophila development. Be sure to explain the role of concentration gradients in syncytial specifications. Do you think Drosophila have “morphogenic fields” or something like them? Discuss an experiment which suggest that they do or do not.

        Syncitial specification is a way to commit cells to their fates, it is an interaction between the parts of one cell. The egg cytoplasm of that that is sanctum is not uniform; the anterior is different from that of its posterior portion. A perfect example of such difference between both portions is Drosophila. The anteriormost portion of the egg has a protein called Bicoid and the posteriormost has one called Nanos, both containing an mRNA that encodes  for each protein. The translation of each mRNA into such proteins occurs once the egg is fertilized. Each protein is highest in concentration at their respective sites, meaning that bicoid concentration is highest at the anteriormost portion and Nanos at the posteriormost portion, both diffusing towards the center of the cytoplasm. Although, such concentration gradients seem insignificant they are essential in the activation of genes for the formation of a specific region of an embryo. There is a coordinate system formed by the proteins, where in each region there is a different ratio of the two proteins to distinguish the parts of the embryo. For example, in the region of the anteriormost, where there is more bicoid and very little nanos it will produce the head. Also, where there is little or none of both then it generates the abdominal structures. Overall, both of these proteins are needed for the determination of the fates of the cells, providing the positional information in the embryo of a Drosophila. A morphogenetic field is a group of cells whose position and fate are specified with respect to the same set of boundaries. Just as is seen with concentration gradient of the protein in the Drosophila,  similarly is seen with the morphogenetic field. In the morphogenetic field, a particular field of cells give rise to a particular organ and even when transplanted to a different part. Due to the transplantation part, I believe Drosophila do have something like morphogenetic fields. For example, in an experiment where cells that would normally become the middle segment of a Drosophila leg were removed from the leg- forming area of the larva and placed into the region that will become the tip of the fly's antenna, differentiating into claws. These cells retain their committed status as leg cells, but respond to the positional information of their environment. The differentiation of those cells depend upon the concentration of that molecule.

5. Define and describe cadherins. Be sure to define and describe the EC domains, post-translational modifications, the cytoplasmic tail and associated molecules and the nature of cadherin-cadherin interaction.

        Cadherins mediate cell adhesion and play an important role in normal development. They establish and maintain intercellular connections. They are important in the spatial segregation of cell types to the organization of animal forms. Overall, these proteins that are calcium dependent transmembrane cell adhesion molecules play an important role in morphogenesis, motility, wound healing, and maintenance of organized tissues. The removal of calcium abolishes adhesive activity and renders cadherins vulnerable to proteases. The most common cadherins consist of  five tandem repeated extracellular domains, a single membrane-spaning segment and a cytoplasmic region. Cadherins interact with other cadherins by anchoring into the cells through catenins; together they form a junction connecting epithelial cells. Cadherin bind to the same type of cadherins on another cell and therefore joining the cells together. Cadherins are able to attach to other cells with E-cadherins and sort out from cells that contain N-cadherin on their membranes; such is called hemophiliac binding. Extra-cellular domains are the parts of receptors that stick out of the membrane on the outside of the cell. There are five extracellular domains but the proteins also have a cytoplasmic tail that gets phosphorylated to bind to cattiness linking it to the cytoskeleton of thecell. Post-translational modification is the enzymatic process of a polypeptide chain after translation from mRNA and after peptide bond formation has occurred. They are essential mechanisms used by eukaryotic cells to diversify their protein functions. After the modification has occurred the cadherin establishes itself as a transmembrane protein with various cytoplasmic and extracellular domains.