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Expression of ribosomal protein genes in mouse oocytes and early embryos
1Developmental Biology Laboratory, VA Medical Center, Sepulveda, California 91343.
Abstract:
The quantitative changes in the mRNAs for ribosomal proteins L7a, L18a, and S15 were assayed in slot hybridization experiments using labeled cRNA probes with total RNA from late growth-phase oocytes, ovulated eggs, and early embryos through the blastocyst stage. All three mRNAs showed a similar developmental pattern of prevalence, but their copy numbers per oocyte or embryo fluctuated according to developmental stage. There are on an average about 17,000 copies of each mRNA in the late growth-phase oocyte; this number drops to one-fifth to one-tenth in the ovulated egg and two-cell embryo but increases rapidly during cleavage to bout 25,000 in the eight-cell embryo and about 42,000 in the blastocyst. A comparison of the levels of these mRNAs with the reported rates of ribosomal protein synthesis (LaMarca and Wassarman, 1979) suggests that, in late growth-phase oocytes, ribosomal protein synthesis is regulated primarily at the translational level and is kept low by some factor limiting mRNA utilization. On the other hand, the high rate of ribosome biosynthesis during early embryogenesis from the two-cell stage onward appears to involve the coordinate activation and transcription of ribosomal RNA and ribosomal protein genes coupled with the immediate translational utilization of ribosomal protein mRNAs.
Insights
Ribosomal protein mRNA levels change significantly during early development. Synthesis regulation shifts from translational control in oocytes to transcriptional control in early embryos.
Area of Science:
- Developmental Biology
- Molecular Biology
- Cell Biology
Background:
- Ribosome biogenesis is crucial for cell growth and proliferation.
- Understanding mRNA dynamics during early embryogenesis is key to deciphering developmental regulation.
Purpose of the Study:
- To quantify changes in specific ribosomal protein mRNAs (L7a, L18a, S15) during oocyte maturation and early embryonic development.
- To investigate the regulatory mechanisms of ribosomal protein synthesis at different developmental stages.
Main Methods:
- Slot hybridization assays were used to measure mRNA copy numbers.
- Labeled complementary RNA (cRNA) probes were utilized for quantification.
- Total RNA was extracted from oocytes, ovulated eggs, and embryos (two-cell to blastocyst stages).
Main Results:
- All three ribosomal protein mRNAs (L7a, L18a, S15) exhibited similar developmental patterns.
- mRNA copy numbers per cell decreased significantly from oocytes to ovulated eggs and early embryos.
- mRNA levels increased substantially during cleavage, peaking in blastocysts.
Conclusions:
- Ribosomal protein synthesis in late-stage oocytes appears translationally regulated due to limited mRNA utilization.
- Early embryogenesis (post-two-cell stage) involves coordinated activation of rRNA and ribosomal protein gene transcription.
- Efficient translational utilization of ribosomal protein mRNAs drives ribosome biosynthesis during early embryonic development.