Developmental capacities of Xenopus eggs, provided with erythrocyte or erythroblast nuclei from adults

Abstract

Nuclei from osmotically opened erythrocytes and erythroblasts were injected into nucleated or enucleated Xenopus laevis eggs. Although the cleavage pattern of the recipient eggs which started to divide was normal in about half of the cases, nuclei from erythrocytes injected into nucleated or enucleated eggs never promoted development beyond the early gastrula stage. In contrast, nuclei from osmotically opened erythroblasts injected into enucleated eggs promoted development to early tadpole stages (stages 29–36). Frequently, injection of osmotically broken erythroblasts injected into nonenucleated eggs gave rise to triploid larvae which all died at roughly the same early tadpole stages (29–36). Surprisingly, development did not proceed to the stage of advanced organogenesis (stages 44–47), which is easily reached by gynogenetic haploids: The presence of the haploid genome derived from the egg pronucleus did not significantly improve the developmental capacity. Embryos obtained by single injection of erythrocyte nuclei into nucleated eggs were unable to pass the gastrula stage. To invalidate the interpretation that the observed arrest in development was related to nuclear damage during injection of the recipient eggs, single unbroken erythrocytes and unbroken erythroblasts were transferred into nucleated and enucleated eggs. No cleavage was observed in both classes of eggs injected with unbroken erythrocytes. In contrast, erythroblasts were found to induce cleavage in the recipient eggs at a frequency of about 11%. To ascertain that the nucleus of unbroken erythroblasts participated in development, the 1-nucleolar marker was used. Diploid embryos with only one nucleolus present were found following injection of unbroken erythroblasts into enucleated eggs from 2 nu females. Triploid 2 nu embryos were detected following injection of (diploid) 1 nu erythroblasts into nonenucleated eggs from 2 nu females. The most advanced development stages reached by these embryos did not, however, differ from the best results found in the first class of experiments: Nuclei from erythroblasts injected undamaged into nucleated or enucleated eggs never developed into a normal tadpole. Serial transfer experiments were performed using normally gastrulating embryos which had developed, following the injection of 1 nu unbroken erythroblasts into recipient eggs. These donors for serial transfer experiments were checked for the presence of the 1 nu marker. In addition they had passed through a normally cleaving eight-cell stage. No improvement in developmental capacity as compared to first transfer experiments could be found.