Quantitative changes in total RNA, total poly (A), and ribosomes in early mouse embryos
L Piko, KB Clegg - Developmental biology, 1982 - Elsevier
L Piko, KB Clegg
Developmental biology, 1982•ElsevierTo obtain information on the amounts and major classes of RNA stored in the mouse egg
and accumulated during cleavage, we determined the contents of total RNA, total poly (A),
and ribosomes from the 1-cell stage to blastocyst. Using purified RNA for assay, we obtained
an RNA content of 0.35 ng in the unfertilized egg, 0.24 ng in 2-cell, 0.69 ng in 8-to 16-cell,
and 1.47 ng in early bastocyst (32 cells). As derived from EM morphometry, the number of
ribosomes accounts for 60–70% of the total RNA content at all these stages; the marked …
and accumulated during cleavage, we determined the contents of total RNA, total poly (A),
and ribosomes from the 1-cell stage to blastocyst. Using purified RNA for assay, we obtained
an RNA content of 0.35 ng in the unfertilized egg, 0.24 ng in 2-cell, 0.69 ng in 8-to 16-cell,
and 1.47 ng in early bastocyst (32 cells). As derived from EM morphometry, the number of
ribosomes accounts for 60–70% of the total RNA content at all these stages; the marked …
Abstract
To obtain information on the amounts and major classes of RNA stored in the mouse egg and accumulated during cleavage, we determined the contents of total RNA, total poly(A), and ribosomes from the 1-cell stage to blastocyst. Using purified RNA for assay, we obtained an RNA content of 0.35 ng in the unfertilized egg, 0.24 ng in 2-cell, 0.69 ng in 8- to 16-cell, and 1.47 ng in early bastocyst (32 cells). As derived from EM morphometry, the number of ribosomes accounts for 60–70% of the total RNA content at all these stages; the marked increase in ribosomal number during cleavage is attributable entirely to new synthesis. Hybridization with [3H]poly(U) in solution yielded a poly(A) content of 0.7 pg for the unfertilized egg and 0.83 pg for the 1-cell embryo. The poly(A) content dropped sharply, to 0.26 pg per embryo, by the late 2-cell stage and increased to 0.44 pg in 8- to 16-cell embryos and 1.42 pg in early blastocysts. Hybridization in situ gave a similar pattern and also revealed a heavy labeling of embryo nuclei from the 2-cell onward but very little, if any, labeling of the pronuclei of 1-cell embryos, suggesting an absence, or low level, of poly(A)+ RNA synthesis at the 1-cell but an active synthesis at the 2-cell and later stages. These findings and other available evidence(e.g., R. Bachvarova and V. De Leon, 1980, Develop. Biol. 74, 1–8) suggest that the mouse embryo inherits a large supply of maternal mRNA but that the bulk of this RNA is eliminated in the 2-cell embryo. In situ hybridization was used to study the relative concentration of poly(A) in ovarian oocytes. In growing oocytes, the cytoplasmic concentration of poly(A) remains about the same, suggesting that the accumulation of poly(A)+ RNA is proportional to oocyte growth. The poly(A) content declines about twofold between the time of completion of oocyte growth and fertilization. The germinal vesicle continues to be labeled up to the time of ovulation, raising the possibility that poly(A)+ RNA synthesis (and presumably turnover) occurs in fully grown oocytes.
Elsevier