Somitogenesis in amphibian embryos. III. Effects of ambient temperature and of developmental stage upon pattern abnormalities that follow short temperature shocks.
Temperature shocks of a few minutes duration at 37 degrees C to tail-bud embryos of Rana induce zones of abnormal segmentation along the somite files subsequently produced. The immediate result of a temperature shock is a temporary arrest of development as a whole, following which the schedule of somite determination and formation is resumed at the normal rate. It is during the period immediately following this that the zone of abnormal somite pattern is determined. Thus the length of the abnormal zone reflects the total time taken by the morphogenetic system to recover from the disturbance, and might depend upon variables affecting both the duration of the initial arrest and the duration of the recovery period itself. Observations are presented demonstrating how the length of abnormal zones, caused by a temperature shock of any particular severity, are affected by three variables; (1) the ambient temperature to which the embryos were adapted before shock, (2) the ambient temperature of post-shock development, (3) the stage in somitogenesis, i.e. the number of somites already formed at the time of shock. The data (in this and previous papers of the series) support models postulating that the spatial periodicity in cell behaviour, that is somite morphogenesis, reflects a normal interaction between two hidden aspects of development, one a wavefront of cellular activation passing down the body axis, and the other having the character of a temporal periodicity throughout the tissue. Temperature shock, as well as halting the wavefront (i.e. stopping development) temporarily, leads to a subsequent period during which there is only gradual recovery of normal co-ordination between the periodicity within cells of the tissue and the wavefront progress. It is the relative rate of this recovery, alone, that is responsible for variation in the length of the abnormal zone.
D000818:Animals; D001699:Biometry; D000013:Congenital Abnormalities / Q000209:etiology; D006358:Hot Temperature; D009024:Morphogenesis; D011896:Rana temporaria / Q000196:embryology*; D013997:Time Factors