Transfer RNA synthesis in early embryogenesis

It has been shown in a number of reports that tRNA in animal and bacterial cells has at least one precursor stage prior to maturation [l-6]. The precursor (pre-tRNA) may be revealed in cells after a very short incubation with label (3-5 min) that suggests a high rate of the pre-tRNA maturation process in a normal cell. Recently we have demonstrated that tRNA synthesis occurs in loach (Misgurnus fossilis L.) embryos at the early cleavage stage [73 in the absence of rRNA and DNA-like RNA synthesis [8,9]. In this paper some characteristics of early tRNA synthesis in loach embryos are described. The main finding is the low rate of maturation process of pre-tRNA. The incorporation was found to occur mostly in the pre-tRNA molecules in embryos at the early blastula stage (5 hr of development) after incubation with labeled uridine for l-2 hr. The mature tRNA synthesis appears in embryos at the mid blastula stage (6.5 hr of development). To elucidate the factors controlling the activation of the tRNA maturation process, experiments were performed with blastoderms (embryos devoid of yolk) isolated at early and mid blastula stage of development and cultivated in vitro. The results obtained indicate that pre-tRNA maturation process is activated in the blastoderm at the mid blastula 6.5 hr stage. In order for the activation to be manifasted at this stage the embryos must be kept intact at the earlier stage.