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9-Roles of the Organizer.pdf

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Biology 3338A
Sashko Damjanovski

•  At the end of gastrulation and neuration have an embryo with the three germa layers and axis •  Everything is in respect to dorsal mesoderm •  Mesoderm frms with dorsal zis on top •  Mesoderm s induced •  Activin is an important player; not the most importnant player but they work •  Activin is a morphogen •  Gooecoid defines dorsal organizer •  Different mesoderms is due to different concentrations of moprogogen 1 •  When gastrulation starts, has tissue above dorsal lip •  Organizer is comitted, gives rise to dorsal mesoderm •  If you put the organizer elsewhere get 2 dorsals •  Dorsal organizer is set up opposite sperm entry point •  First cleavage plane defines left and right, goes through the organizer •  Grey crescent develops; tells where dorsal is because of crodical rotation •  If divide embryo and don’t give it grey crescent, develops abnorally •  If ectoderm is transplanted before it is indeced, it will remian ectoderm •  If wait unitl gastrulation prgresses; ectoderme is being induced and changed(knows position is neural). If transplant to another embryo will form neural tissues 2 •  Red band forms mesoderm •  If take ac and vp, and put them together, will stell get signalling and form mesoderm (wont get any patterning) •  PCR for mesodermal genes. If take late state change embryo that has a heart, will have the gene (cardiac actin). Wont have any in ac, wont have them in vp. However if u put ac and vp together, may get cadiac actin (induced the right type of actin) 3 •  Organizer is responsible for 1o embryonic inductuion •  4 function: 1. Make something called the prechordal plateà self determing, forms this all by itself 2. Starts off as ring of mesoderm. Notochord (dorsal mesoderm). The closer u are to them, the more dorsal character you are. Its whats maing somites dorsal. 3. Makes ectoderm near it neural, because of signalling 4. Intiates gastrulation 4 •  Cortucal rotationà rotates respect to inside of egg •  Does so because of mt lining cortex, outside of egg •  Before fert, mt will not be organized, after fert mt much better organized, soerm bring centriole •  Centriole of mt organized centrer; beofre centrioles play role in mt apparatus. Centriole is mtoc allows mt to polmerate away from sperm that just came in •  Provides track •  When it rotates, cytoplasm floats around. When it swirls, able to see the grey crescent (dorsal side). First cleavage goes theough the grey crescent 5 •  Dsh is on vegetal side in cortex •  Sperm ferts in animal half. When fert brings in centriole. When centriole comes in; polymerizes green tract. Causes rotation of the cortex (causes things insde to swil around), also gives dsh a tract to move. Kinesin moves dsh to move. •  Polymerization downwards in respect to gravity. If gravity isn available polymerizes in one direction •  Dsh moves opposite of s.e.p; wherever spot of dsh is is where dorsal is •  Dsh inhibits gsk3. gsk3 is everywhere in embryo. If dsh is on one side of emrbyo, inhibits gsk3, allowing b catenin to survive. End up with gradient of b cattenin on one side of the egg, and none on the ther •  This is all happening before the first cleaveage •  By the time gastrulation starts, cell on one side will have beta cetenin, other side wont.Area with high levels of beta catenin forms dorsal •  LiCl inhibits gsk3. beta catenin then is allowed everywhere. Embyo becomes dorsalzed, and tries to form dorsal everywhere •  UVà put bottom of egg under uv light. Basically depolymerizes and intferes 6 •  Has not been any transcription yet. •  Tcf 3 is found everywhere in the cell. In absence of b-cat, tcf 3, it is a repressor. In presence of b-cat tcf3 causes transcitpion of siamois and twin (found in dorsal) •  Don’t necessarily have dorsal organizer yet (need more specificity) siamois and twin turn on transciption of dorsal organizer gene goosecoid. 7 •  B cat turns on genese with help of tcf 3. turns on siamois and twin, needs smad input. •  Smad comes in where
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