| dc.description.abstract | By virtue of its inheritance of polar lobe material, the D macromere signals the overlying micromeres to develop specialized ectodermal structures (Clement, A., J Exp Zool. 149:193). The first quartet micromeres 1a, 1b, 1c and 1d contribute to the larval head. The left and right eyes arise from 1a and 1c (Render, J., Dev. 113:495), and they will not develop if these cells are removed (Clement, A., J Exp Zool. 166: 77). When the 1a micromere is transplanted to its normal position at the eight cell state, the left eye develops in 38% of the cases. Similarly, when the 1b micromere is transplanted to the position of 1a, the left eye develops in 37% of the cases, indicating that 1b has the same ability to develop an eye as 1a. The 1a micromere never develops an eye in the position of 1b. These findings suggest that 1a, 1b, and 1c may become specified to develop an eye only if they are in close proximity to the inducing D macromere. To further test this hypothesis, the 1a or 1b micromere was transplanted to the position of 1d, the closest first quartet micromere to the inducing D cell. An ectopic third eye develops from the transplanted cell in 42% of the cases. The 1d micromere in the 1a position develops the left eye in only 2% of the cases. This suggests that the 1d micromere has an impaired ability to respond to the inductive signal compared to 1a, 1b, and 1c. Because the 1d micromere is the only first quartet micromere that may inherit polar lobe material, it is possible that cytoplasmic factors restrict this cell from developing an eye in response to the inductive signal. | en_US |
