Control of RNA content of developing human placenta

Area of Science:

• Reproductive Biology
• Molecular Biology
• Biochemistry

Background:

• The human placenta undergoes significant functional and molecular changes throughout pregnancy.
• Understanding placental gene expression regulation is crucial for fetal development.

Purpose of the Study:

• To investigate changes in RNA content, RNA polymerase activity, and chromatin template availability in human placentae from early to full term.
• To determine the molecular mechanisms underlying reduced RNA content per cell in late-term placentae.

Main Methods:

• Quantification of RNA and DNA content.
• Assay of RNA polymerase types and activities in isolated placental nuclei.
• Measurement of chromatin template availability for RNA polymerase II transcription.
• Use of alpha-amanitin and DEAE-Sephadex chromatography for polymerase characterization.

Main Results:

• The RNA:DNA ratio decreased from 0.7 (15-20 weeks) to 0.4 (40 weeks).
• RNA polymerase II constituted 55-60% of total RNA polymerase activity at both stages.
• Despite a 20% increase in polymerase activity, template availability for RNA polymerase II decreased by 70% in full-term placentae.
• Reduced RNA content was attributed to decreased synthesis, not increased degradation.

Conclusions:

• Reduced template availability in full-term placental chromatin significantly limits RNA synthesis.
• This decrease in template availability more than compensates for the slight increase in RNA polymerase activity.
• The findings highlight a critical regulatory mechanism impacting placental gene expression during late pregnancy.