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Developing somitic stage zebrafish embryos treated with valproic acid displayed a number of somite anomalies. These anomalies were grouped into two classes as formulated by Smith and Tuan (1996). Class I anomalies refer to a discrete fusion of an adjacent pair of somites or a mis-segmentation of a single somite. Class II anomalies refer to regions devoid of new somite formation or containing disorganized or "scrambled" somites (Smith & Tuan, 1996). Normal zebrafish somite development begins at approximately 10-11 hours after fertilization. Our embryos were fixed and stained at 28 hours after fertilization resulting in embryos containing a number of somites. Overall results showed a general trend of mortality with increasing concentration of valproic acid (Table I) following a dose-dependant pattern.
The percent of embryos displaying valproic acid induced somite anomalies varied according to valproic acid dosage. At low dosages of valproic acid, 0.025M and 0.05M, the zebrafish embryos exhibited somite irregularities characteristic of Class I anomalies
(Figure 3). In comparison to control embryos (Figure 2) in which no valproic acid was used, the experimental embryos lacked pigment and were smaller in size. Additionally, the somite patterning at these dosages displayed a discrete fusion of adjacent pairs of somites (Figure 3). As the dosage increased, so did the somite abnormalities. Embryos treated with 0.1M valproic acid solution were characteristic of Class II anomalies, displaying disorganized and scrambled somites in the tail region (Figure 4). Also, these embryos lacked pigment and appeared smaller in size as compared to the control embryos. The highest dosage of valproic acid, 0.2M, was lethal to developing embryos as no embryos survived (Figure 5).

© Cebra-Thomas, 2001

Last Modified: 31 May 2001

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