Biology 441, Spring 2013: Lecture notes for January 30
Embryonic Induction Discovered by Hans Spemann & Hilde ProschöldTransplantation of dorsal lip of the blastopore of salamander embryos
Put into the blastocoel of another salamander embryo
Still unknown chemical signals from the grafted pre-notochord and pre-somite mesoderm stimulate change in differentiated fates of nearby somatic ectoderm so that it forms a second neural tube
Also, nearby lateral plate mesoderm converts to forming somites, etc.
Proschöld dies from stove fire soon after this discovery
Many more examples of induction are discovered
Subdivision of embryos into parts*Blastula stage blastoderm (in birds) blastocyst (in mammals)
*Gastrulation: subdivision of the developing embryo into 3 primary germ layers
Ectoderm is mechanically subdivided into three subdivision by the neurulation process
Somatic ectoderm forms the outer layer of the skin (epidermis) & "placodes"
Neural crest ectoderm forms sensory nerves, autonomic nerves, pigment cells etc.
The lining of the mouth is stomodeal ectoderm
Mesoderm subdivides into:
Lateral Plate mesoderm
Myotome (whose cells will differentiate into skeletal muscles)
Dermatome (the cells of which will become the inner layer of skin, the dermis)
male sex ducts
Uterus, and female sex ducts
Esophagus, stomach (the lining) which is surrounded by lateral plate mesoderm
Intestine (lining) which is surrounded by lateral plate mesoderm
salivary glands (although some salivary glands are stomodeal ectoderm)
cloaca (which only in mammals gets subdivided into the following)
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