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Heat shock treatment at 40.0C resulted in somite development disturbances. Under normal development, motoneurons are located in the median of the somite relative to its anterior-posterior axis; however, in the heat-shocked embryos, the distance between the anterior of the somite and the axon increased or decreased, and we assume that the disruption in the somite development pathway is the cause for both the variation in somite size and placement of motoneuron axons in the heat shocked embryo (Figure 2)(Roy et al., 1999). Since l-fringe is so crucial in the development and separation of somites, higher incubation temperatures most likely interfered with the normal fringe pathway, leading to varying placement of motoneuron axons. Motoneuron axons seem to be important in determining the size of the somite.

L-fringe and the Notch pathway have been discussed in literature as having an important role in somite formation (Holley and Takeda, 2002; Jiang et al., 2000; Forsberg et al., 1998). A disruption along the pathway leads to malformed structures, and since the signals are sent in a dynamic wave pattern, this is probably the cause of the multiple disruptions that Roy and his colleagues found. Although there were no multiple disruptions in this experiment, there is no evidence to suggest that the disturbances occurred by other means. In addition, there was a zone of regular development before the abnormal somite, leading us to believe that the early components of the pathway is more susceptible to heat shock. Future investigation involving heat stability of fringe or Notch can pinpoint the actual pathway and provide further insight into somite development.

The embryos were incubated in shallow glass dishes, and drying out probably caused some of the embryo deaths. In addition, viewing the staining was much easier in the embryos that hatched out of their chorions, whereas viewing was difficult in the embryos that were still curled up. In future experiments, it would be beneficial to allow the embryos to hatch, a procedure that would also make the dechorionating step obsolete. However, disturbance in several treated embryos and none in the control embryos provides strong evidence that heat shock does lead to malformation of somites.

©Cebra-Thomas, 2000

Last Modified: 10 May 2004

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