The determination and positioning of the nose, lens and ear. III. Effects of reversing the antero-posterior axis of epidermis, neural plate and neural fold
✍ Scribed by Jacobson, Antone Gardner
- Publisher
- John Wiley and Sons
- Year
- 1963
- Tongue
- English
- Weight
- 804 KB
- Volume
- 154
- Category
- Article
- ISSN
- 0022-104X
No coin nor oath required. For personal study only.
✦ Synopsis
To account for the anteroposterior distribution in the developing embryo of noses, lenses and ears there are several possibilities. An attractive hypothesis is to relate this specificity to the different neural inductors of these organs. Specific inductor substances from forebrain would specify nose formation from the epidermis, substances from the retina would specify lens formation, and substances from the hindbrain would specify ear formation. This hypothesis is not by itself sufficient since noses, lenses and ears can form in reasonably proper order in embryos lacking the entire neural plate (Jacobson, '63a).
Another likely source of qualitatively different inductor substances distributed along the antero-posterior axis is the endoderm which is itself, at early neurula stages, largely a mosaic of future organ parts. However, normally positioned noses, lenses and ears form in endoderm-free embryos and also in embryos in which the antero-posterior axis of the endoderm has been reversed (Jacobson, '63b).
It is not a simple matter to test the mesoderm for its capacity to position nose, lens and ear. However, embryos lacking all mesoderm and all endoderm can form normally positioned noses, lenses and ears; so the mesoderm cannot be all important (Jacobson, '63b).
In explant, the prospective placodal epidermis of the early neurula forms no noses, lenses or ears when isolated alone, and forms normally positioned noses, lenses and ears only when neural plate, neural fold, mesoderm and endoderm are all present (Jacobson, '63a).