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Biology 3338A
Sashko Damjanovski

•  Looking at the dorsal side of a chcik embryo; ectoderm has been removed •  Without ectoderm can see different structures •  Struture in middle is neural tube, underneath neural tube is nortochord •  Lateral to neural tube is mesoderm •  Mesoderm is starting to change its shape; posterior is solid sheet, but more anterior starts to differetiate •  Dffernetiation of mesoderm occurs anterio posterior in chick; likewise somitogensis •  Right next ot enural tube, mesoderm is called paraxial mesoderm •  Paraxial mesoderm is unsgmeented mesoderà in birds called the plate •  Paraxial starts to separate itself form lateral mesoderm and forms repeatirng structures called somites •  Somites play a role in migration of neural crest cells etc. 1 •  Top right: chick embyo going through gastrulation. First thing tat happens is form nortochord. Northochord is the first thing to differentiate. Once differentiated, next mesoderm, latearally is parzial. Starts to segment. The more lateral you go, the more mesoderms •  If anything left of the norochord, becomes invertebral disk…mst of it however dsngerates •  RECAP •  Chick embryo; gas occurs and make mesoderm •  Mesoderm is initlaly one solid tissue, but differentaites into differetn meso •  One of the first meso is nortochord (dorsal meso) •  Going outward get different kinds 2 •  On either side of neural tube is prax •  Parax sgemtns anter to post •  Notch signalling is important; expressed at boundary of segments •  If transplant notch cells to different area, new area will form a boundary •  If transplant cells that don’t have notch, no biundary…but inject notch in them, form boundary •  Notch is turning on expression of genes: ephrin and eph •  Ephrin is a ligan, eph is a receptor •  When they signal t each other, get cell cell repulsiln •  RECAP •  Notch signallig is needed for formation of fissures •  Notch associated with eph; other cells have ephrin…causes signanling cascades where hey repel 3 •  Wave of acrivation.Activation only occurs when notch is present •  Only at anterior most part is there repulsion •  What controlsperiodicity is hairy •  Timing is regulated by hairy •  Domain of hairy rxpression shifts form most of mesoderm to area that forms the bounday •  Starts being expressed more at posterior. Shifts and is expressed where the fissire occurs •  Hairy expression Is periodic •  RECAP •  Hairy xontrols periodicity •  Airy and eph on posterior. Its when hairy (conincides with notch) becomes restricted, that formation of fissure is activated •  Hairy is found theough all of paraxial meso, becomes restricted •  As hairy becomes restricted, fissure is formed •  Hairy is cyclic; goes from posterior to anterior 4 •  Lateral tyoe of mesoderm is mesech
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