MicroRNA expression in bovine preimplantation embryos

Area of Science:

• Reproductive biology
• Molecular biology
• Genomics

Background:

• MicroRNAs (miRNAs) are crucial regulators of gene expression.
• Understanding miRNA dynamics during early bovine development is essential for reproductive success.

Purpose of the Study:

• To quantify absolute miRNA levels in various stages of cattle oocytes and embryos.
• To assess the functional implications of miRNA concentrations for gene regulation.
• To compare miRNA profiles between normal and parthenogenetic bovine embryos.

Main Methods:

• Profiling of 98 mature human microRNAs using stem-loop reverse transcription polymerase chain reaction (RT-PCR) array.
• Absolute quantification of miRNA copy numbers in cattle oocytes, eight-cell embryos, blastocysts, and Day-14 trophoblast.
• Analysis of miRNA expression in normal versus parthenogenetic embryos.

Main Results:

• Most miRNA concentrations were below the functional threshold for effective target repression.
• miRNA 320 was highly abundant (>1000 copies/embryo) in oocytes and peri-embryonic genome activation embryos.
• miRNA abundance per cell increased from the eight-cell to blastocyst stage, but decreased in Day-14 trophoblast.
• Parthenogenetic embryos exhibited distinct miRNA expression profiles, with overexpression of miRNAs 299 and 323.

Conclusions:

• Early bovine embryos and oocytes generally possess low levels of functional miRNAs, with notable exceptions like miRNA 320.
• Developmental stage significantly impacts miRNA abundance and species diversity.
• Parthenogenesis influences miRNA expression patterns, suggesting a role in developmental abnormalities.