Biology 441, Spring 2013: Lecture notes for January 30


Embryonic Induction Discovered by Hans Spemann & Hilde Proschöld

Transplantation 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
Spemann becomes even more famous
Spemann wins Nobel Prize for discovering induction

Many more examples of induction are discovered
(tissues signal change in differentiation of nearby cells)


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

    Neural tube ectoderm forms nervous system

    Somatic ectoderm forms the outer layer of the skin (epidermis) & "placodes"

    Neural crest ectoderm forms sensory nerves, autonomic nerves, pigment cells etc.

      {Facial Skeleton is also formed by neural crest! which is strange}

      The lining of the mouth is stomodeal ectoderm
      made of cells from the stomodeum invagination

Mesoderm subdivides into:

    Intermediate mesoderm
    Lateral Plate mesoderm

    Each somite subdivides into
      Sclerotome (the cells of which will differentiate into cartilage and bone)
      Myotome (whose cells will differentiate into skeletal muscles)
      Dermatome (the cells of which will become the inner layer of skin, the dermis)

    The Intermediate Mesoderm subdivides into...
      3 pairs of kidneys
      male sex ducts

    The Lateral Plate Mesoderm subdivides into...
      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
    thyroid gland
    salivary glands (although some salivary glands are stomodeal ectoderm)
    cloaca (which only in mammals gets subdivided into the following)


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