Presentation on theme: "Genetics of Axis Specification in Drosophila: Dorsal-Ventral Axis Specification Gilbert - Chapter 9."— Presentation transcript:
1 Genetics of Axis Specification in Drosophila: Dorsal-Ventral Axis Specification Gilbert - Chapter 9
2 Today’s GoalsDescribe the use of a Genetic screen to identify functionality of individual gene productsIdentify Eric Weischaus and Christianne Nusslein-VolhardIdentify key molecular players in establishing polarity and segments in various types of embryosDefine the term “positional information”Describe how evolutionarily conserved genes play similar roles in development of a wide variety of speciesDefine transcription factor
3 Generating Dorsal-Ventral Pattern in the D. melanogaster embryo During the genetic screen for fruit fly embryonic genesDiscovered a gene called DorsalMutation is SEVERE - no VENTRAL side!Maternal Effect geneDorsal mRNA Placed in the oocyte by nurse cells
6 Dorsal ProteinAlthough mRNA is placed in the egg by mother, dorsal does not work like bicoidWhen the protein is translated, there is NO gradient formedRather, dorsal protein is found throughout the embryo!How can this serve as positional information to make a ventral side??
7 The Answer! Dorsal is a transcription factor Where in the cell should it function??
9 Dorsal Protein become Translocated to the Nuclei For this transcription factor to function, it must enter the nucleusAlthough Dorsal protein is expressed throughout the egg cytoplasm, once cells have begun to form . . .Dorsal protein enters the nuclei of JUST THE VENTRAL-most cells!
10 In the Dorsal MutantDorsal doesn’t enter the nuclei in the ventral cellsNo genes to specify “Ventral” are activatedGenes that specify “Dorsal” are not repressed
11 Answers always lead to more questions! How does Dorsal protein enter ONLY the nuclei of the ventral cells??When first produced, Dorsal is complexed with a protein called Cactus in the cytoplasm of the developing embryoAs long as Cactus Binds to dorsal, dorsal cannot enter the nuclei
15 Let’s take a look the Pathway! Ventral Follicle cells (nurse cells) release paracrine signalsPipe along with a protein called “Factor X”These bind to Nudel outside the cellIn the space between the follicle cells and the ventral embryonic cells:Nudel enzymatically splits the Gd protein (gastrulation deficient)
17 MORE! Gd cleaves the Snake protein Snake cleaves Easter Easter cleaves SpätzleSpätzle is the ligand for the Toll receptorBinds to TollToll activates Pelle - A protein KinasePelle phosphorylates CactusCacus gets degraded, releasing dorsalDorsal enters the nucleus
18 What does Dorsal do once it enters the nucleus? What are the DOWNSTREAM events that are activated by Dorsal transcription factor?Cells that express the highest amounts of dorsal in their nuclei become mesoderm!Helps to initiate gastrulation!
20 Dorsal - Downstream Factors Dorsal initiates transcription of genes involved in mesoderm specification, and gastrulationTwist, snail, Fgf-8OF COURSE, it is always more complicated than just the examples I am showing :)
24 Dorsal-Ventral Patterning Summary D-V patterning in the fruit fly embryo has similarities to A-P patterning, yet is uniqueUses positional information to specify regions of the embryoIncorporates cell-cell signaling to convey positional information in some cases