Nerve commitment in Hydra. II. Localization of commitment in S phase.

The kinetics of nerve differentiation were investigated during head regeneration in Hydra. In particular the cell cycle parameters of stem cells undergoing nerve commitment were determined. Head regeneration induces extensive nerve commitment localized at the regenerating tip (G. Venugopal appearance of committed nerve precursors is followed 12 hr later by the appearance of newly differentiated nerves. Under these conditions the time from the end of S phase to nerve differentiation is about 9 hr and the time from the beginning of S phase to nerve differentiation is about 18 hr. Thus nerve commitment occurs in mid-to late S phase of the stem cell precursor.