THE HEAD ACTIVATION GRADIENT MORPHALLAXIS REGENERATION
17.2.1. The head activation gradient
Hydra has a columnar body along the apical-basal axis formation of both the head and the foot. A series of morphogenetic gradients define the polarity of the hydra that permits the formation of the head only at one place and the basal disc formation only at another. If transplantation of hypostome tissue of one hydra takes place into the middle of another hydra, then the formation of a new apical-basal axis takes place along with the hypostome extending outward. Same case with the basal disc, but here the opposite polarity and extending a basal disc. If transplantation of tissues from both ends occurs simultaneously into the middle of a host then no new axis is formed or if the form has little polarity. These experiments have been deduced the presence of a head activation gradient, which is highest at the hypostome along with foot activation gradient which is highest at the basal disc.
17.2.2. The hypostome as an "organizer"
Hypostome of the hydra act as an "organizer" Because hypostome cause induction of formation of secondary axis if transplanted in the host, hypostome cause the production of both head activation along with head inhibition signals, the hypostome act as "self-differentiating" region, the head inhibition signal cause the inhibition of the formation of new organizing centers.
Three genes are important for hypostome function in hydra. First Wnt, crucial for the hypostome region during the bud elongation and Wnt present at apical region and inhibit GSK3 as a result stabilization of β catenin in the cell nucleus takes place.
- CLEAVAGE AND AXIS FORMATION IN C. ELEGANS
- ANTERIOR POSTERIOR AXIS DIFFERENTIATION IN DROSOPHILA
- SEA URCHIN GASTRULATION
- XENOPUS GASTRULATION
- MATING SWITCH
- MORPHOGENESIS AND ORGANOGENESIS IN AMINALS
- CELL AGGREGATION AND DIFFERENTIATION IN DICTYOSTELIUM
- LIMB DEVELOPMENT AND REGENERATION
- DEVELOPMENT OF NEURONS
- LARVAE FORMATION
- SEX DETERMINATION
- EYE LENS INDUCTION
- THE ABC MODEL OF FLOWER DEVELOPMENT