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DB5notes - BIOLOGY 205/SECTION 7 DEVELOPMENT-LILJEGREN...

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BIOLOGY 205/SECTION 7 DEVELOPMENT-LILJEGREN Lecture 5 Gastrulation 5. The dorsal/ventral axis in the frog a. Mother sets up initial axis of polarity: animal & vegetal poles b. sperm entry is the critical cue in setting up the dorsal-ventral axis and results in formation of the blastopore 180° opposite sperm entry point . How does this work? c. Sperm enters randomly at one side of the animal hemisphere 1.) Entry of sperm nucleus leads to cytoskeletal rearrangements which lead to 30 ° rotation of outer cortex relative to inner cytoplasm . 2.) This rotation leads to juxtaposition of animal pole cytoplasm with vegetal pole cortex , and forms an area called the gray crescent . The gray crescent region in the fertilized egg marks the future site of the dorsal blastopore lip in the later embryo starting to undergo gastrulation. 6. Experiments in Gastrulation a. Experiment #1 - determine basis of gray crescent formation i. Rotate egg so that sperm entry point is now on top. ii. Prevents normal 30 ° cortical rotation. iii. As a result: 1. Inner cytoplasm shifts due to effects of gravity 2. New region of juxtaposition of animal pole cytoplasm -- vegetal pole cortex next to sperm entry point 3. Blastopore forms there instead. Conclusion: juxtaposition of animal pole cytoplasm to vegetal pole cortex is critical factor! Induction 1) In the first lecture, we talked about how cells can get information from neighbors which can influence their cell fate. Today we’ll be talking more in detail about the kind of signaling that can communicate information between cells. a)
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DB5notes - BIOLOGY 205/SECTION 7 DEVELOPMENT-LILJEGREN...

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