Pattern Forming Reactions and the Generation of Primary Embryonic Axes
Abstract
- 1.
The wavelength problem: Patterns generated by the Turing reaction diffusion mechanism have a characteristic wavelength. Upon growth a transition from a polar pattern into a symmetric and ultimately into a periodic pattern is expected. However, in many developing systems substantial growth is possible without losing the polar character. It is proposed that the maintenance of a polar pattern is accomplished by a feedback of the pattern on the ability of the cells to perform the patterning reaction, i.e., on their competence. Cells distant to a once formed organizing region lose the competence to form additional maxima, making the first formed maximum dominate.
- 2.
The midline problem: The formation of a coordinate system for a bilaterally symmetric organism requires the formation of a midline, i.e., a reference line and not a reference point for the mediolateral patterning. The formation of a single straight line requires the cooperation of a spot like and a stripe-like system. In vertebrates the midline is formed by a local elongation under the influence of the organizer. ‘In contrast, in insects an inhibitory influence from a local dorsal organizer allows midline formation only ventrally.
- 3
The left-right pattern: It is proposed that the midline signal induces the ‘left’ signal but higher levels of the midline signal repress the ‘left’ signal. Therefore, the ‘left’-signal has to escape from the midline to a lateral position. This mechanism needs only a minute asymmetry for a reproducible shift to the left. it accou if the systematic asymmetry L. lost.
Keywords
Polar Pattern Oral Opening Single Straight Line Spot System Germ RingPreview
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