Paternally expressed genes predominate in the placenta.

Area of Science:

• Genomics
• Developmental Biology
• Epigenetics

Background:

• Genomic imprinting influences mammalian development, with the paternal genome suggested to be crucial for placental growth.
• Previous studies lacked clear evidence for paternal bias in imprinted gene expression.

Purpose of the Study:

• To investigate paternal bias in imprinted gene expression during placental development.
• To identify novel imprinted genes and characterize their expression patterns in horse-donkey hybrids.

Main Methods:

• RNA sequencing of trophoblast tissue from reciprocal horse-donkey hybrids for parent-of-origin gene expression analysis.
• Pyrosequencing to validate imprinting status of selected genes.
• Comparison of gene expression in placenta versus fetus.

Main Results:

• Identification of 15 ancient imprinted genes, with 10 showing paternal expression.
• Discovery of 78 additional candidate imprinted genes with paternal bias in the placenta.
• Confirmation of imprinting for genes including insulin receptor (INSR) and histone acetyltransferase-1 (HAT1).
• Observed parent-of-origin bias in placenta but not fetus for candidate genes.
• Incomplete silencing of imprinted alleles and inter-individual variability in imprinting status.

Conclusions:

• Genomic imprinting exhibits significant paternal bias in mammalian placental development.
• Imprinted gene expression in the placenta is plastic, with variable silencing and inter-individual differences.
• Placental epigenetic signatures contribute to intrauterine environment variation, allowing for natural selection.