Abstract
During the normal development of the loach embryo the aldolase activity remains constant until the appearance of the first somites (21 hr at 21.5°C). After that it decreases sharply twofold (by 23 hr), whereupon it starts to increase gradually reaching a maximum level by the onset of embryo movement (36 hr). The time of functioning of the genes controlling the decrease and subsequent increase of aldolase activity was defined by inactivation of nuclei by actinomycin D or heavy doses of ionizing radiation at successive developmental stages. It was shown that two nonoverlapping periods exist in the functioning of the genetic apparatus. The first (15–18 hr) is responsible for the rapid inactivation of old (maternal) aldolase, whereas the second (21–27 hr) is responsible for its subsequent substitution by new embryo aldolase. The existence of the latter was confirmed by experiments on hybrids between loach and some more thermophilic species of fish, the aldolase thermostability level being used as a genetic marker. The functioning of genes determining the new aldolase synthesis and those responsible for morphogenesis at respective stages are not coincident in time. Thus, it is likely that biochemical and morphological differentiations proceed to a certain extent independently.
Published Version
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