Question

Developmental Biology

Discuss how the dorsal-ventral axis is established in amphibian or fish embryos. You should include in your answer the names of the most important molecules. Feel free to discuss manipulations such as knockouts that have provided evidence.

Answer 1

WWW . Ansuner In case of amphibian, the axis - formation en the frog (Xenopus) is the most studied and is the model organism. Dorsal-Ventral axis specification in Frog egg es meso lecithal with moderate amount of you. Aminal pole h Puner animal cytoplasm cortical cytoplasm. 1 Equatorial plane t-megetal cytoplasm. to vegetal pole frogs egg The frogs egg is divided into 2 poles - the animal pole and the vegetal pole based on the position of the egg poolt you. The cytoplasm of the egg in the animal hemisphere is divided into 2 parts - the outer cortical cytoplasm which is dasli and piginented and the inner cytoplasm which is light in colour. throughout the egg The sperm enters the egg. through and point on the animal hemisphere it I as the 1st determining fador for the dorsal ventral ax side cide from which the sperm enten mes the ventral side while the the Dorsal side becomes opposite side e in from The side

Collowing sperm entry the cortical cytoplasm, undergoes a 30° cortical rotation towarrdo e direction of sperm entry. This phenomenon xposes the clear cytoplasm from the vegetal risphere to the animal hemisphere. this ortion is called the Gray Crescent spermentary hemispher 7 cortical cortical cytoplasm cytoplasm Punercy hoplana 21]> giore cent 4 Equator Z vemosphere tregetal pole Mont Vegetal of certae to the dorsal that inhobeli the cortical rotation causes the movement cortain proteins from the vegetal pole the dorsal side. The main member include a proteen called Deishvelled (osh) it inhobils GISK-3 activity, and bilizes the concentration of Bi-catenin lenin is distributed uniformly oughout the egg but get activated on the dorsal side because ein aces it is in hibited by G.sa-3 to dorsal side Dsh block is a ß-catenin other places it is abon but in the dorsal side o G.sk:3 and hence B - catenen activated GSK -3 B-calinen H Dsh- GBP wat in Dsh/Wntill GBF Apart from Dsh other proteins like wnt il and GBP (GSK binding protein also helps here

active throughout Cinitially) BMP-A - After organizer activated Отасиі ел Земед - 4PMP4 м Рох са ride Now Brcat along with 2 proteins called . Neg I and vg 1 activates the expression of nr 1 (Xenopus nodal related ene 1). This. forms the organizer tissue ... chile the prescence of only reg T and ugl in the absence of B - caterin us the Mentral side forms the ventral mesoderm vegt & rg 1 + Beatenin organizer (Dorsal) vegetal ventral mesoderm Hemisphere Pri this way the vential and Dorsal specification is sone. completed Ventral B-cat (-) xnr dl BMP 19. Dorsal Beat (t) xnr an. BMP IV -This This agamoment invagination organizer helps to initiate the of cina gastrulation forming a alled the blastopare that actually the horms future The anus in Xenopus read Starti üragination dorsal rip of Blastopore are initial movement l'invad cells during gastrulation pore called the bla startit Bio of cells that notre from the dorsal lip called Bottle cells.

: The process of dorsal ventral specificales has been provided by Knochout experiment - Dsh knockout no organizer B- catenen - - 3 secondary a formed Br car where cout) Хе .. CGsu- 3 knockout - Organizer transplanted to. ventral side & secondary axis - formation, 2 organizer B calenin performs the main role a of B-eatenin removal the inhibits rentral specification as well as form of the organizer it u as the dorsal formation

The developmental process involves numerous signaling pathways and cell interaction through induction and sometimes through morphogen gradient.The organizer also known as Spemann - Mangold organizer is the main signalling centre that contains numerous genes whose expression and activation through specific pathway and cellluler interaction guides the development of the Xenopus early embryo stages.