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Published on: November 11, 2014
Repetitive sequence transcripts in the mature sea urchin oocyte.
Cell
|September 1, 1978
Summary
Mature sea urchin oocytes express repetitive DNA sequences in their RNA. Most short interspersed repetitive sequences and many long repetitive sequences are transcribed, with varying prevalence levels.
Area of Science:
- Molecular Biology
- Developmental Biology
- Genomics
Background:
- Interspersed repetitive sequences (IRS) are abundant in eukaryotic genomes.
- Their expression in oocytes is crucial for early development.
- Understanding IRS transcription in sea urchin oocytes provides insights into genome regulation.
Purpose of the Study:
- To investigate the expression of short and long interspersed repetitive sequences in mature sea urchin oocytes.
- To determine the prevalence and strand representation of these transcribed repetitive sequences.
- To correlate transcript prevalence with genomic reiteration frequency and genomic organization.
Main Methods:
- Preparation of 3H-DNA tracers for short (hundreds of nucleotides) and long (approx. 2000 nucleotides) interspersed repetitive sequences from Strongylocentrotus purpuratus genomic DNA.
- Hybridization of these tracers with excess mature oocyte RNA.
- Analysis of kinetics to determine transcript prevalence.
- Strand-separation and hybridization of nine cloned repetitive sequences with oocyte RNA.
- Analysis of genomic organization of transcribed repetitive sequences.
Main Results:
- Approximately 80% of short repeat tracers and 35% of long repeat tracers hybridized with oocyte RNA.
- Transcripts complementary to both strands of most repetitive sequences were detected.
- Transcript prevalence varied widely, from approximately 10^3 to over 10^5 copies per oocyte.
- Transcript prevalence was independent of genomic reiteration frequency.
- Prevalent transcripts originated from repetitive families with low genomic copy numbers (<200 per haploid genome).
- Most members of prevalent transcript families are interspersed with single-copy sequences.
Conclusions:
- Mature sea urchin oocytes actively transcribe a significant portion of their interspersed repetitive sequences.
- Both short and long interspersed repetitive sequences are represented in oocyte RNA, with varying prevalence.
- Transcript prevalence is not directly linked to the copy number of the repeat in the genome, suggesting complex regulatory mechanisms.
- The findings highlight the dynamic expression and genomic organization of repetitive elements during oogenesis.
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