Basic Introduction to Epigenetics and Sperm-Specific Epigenetic Signatures

2. Epigenetics

3.  The word ‘epigenetics’ means roughly ‘above genetics’ or ‘in
addition to the genome’.
 Epigenetics describes mechanisms that lead to changed,
heritable structural and activation states of the chromatin
without changes to the primary nucleotide sequence.
Introduction:
Walter, J., & Hümpel, A. (2017). Introduction to epigenetics. In Epigenetics (pp. 11-29).
Springer VS, Wiesbaden.

4.  All cells in an organism have very different phenotypes
despite having the same genome.
 Epigenetics modulates and regulates gene expression
through various “epigenomic marks”.
 It is a term given to chemical compounds added to DNA or
histone proteins and recognized by enzymes that either lay
down or remove the specific mark.
Epigenomic Marks:
Tiffon, C. (2018). The impact of nutrition and environmental epigenetics on human health
and disease. International journal of molecular sciences, 19(11), 3425.

5. Environmental Epigenetics:
 “Environmental epigenetics” refers to how environmental
exposures affect epigenetic changes.
 Behavior, nutrition, and exposure to toxins and pollutants are
among the lifestyle factors known to be associated with
epigenetic modifications.
 Example: Nutrition.
 Life experiences, habits, and our environment shape what
and who we are by virtue of their impact on our epigenome
and health.
 Example: Identical Twins.
Tiffon, C. (2018). The impact of nutrition and environmental epigenetics on human health
and disease. International journal of molecular sciences, 19(11), 3425.

6. Sperm Specific Epigenetic Signatures:
 Sperm cells show many characteristic epigenetic features.
Schagdarsurengin, U., & Steger, K. (2016). Epigenetics in male reproduction: effect of
paternal diet on sperm quality and offspring health. Nature Reviews Urology, 13(10), 584.

7. Histone-Protamine Exchange:
 An important phenomenon in haploid spermatids is the
replacement of the majority of DNA-binding histones by
protamines.
 This process can be considered a sperm-specific epigenetic
mechanism, as protamine-induced high-order chromatin
packaging results in a global stop of transcription.
 Abnormal histone–protamine exchange followed by
protamine deficiency is related to both increased sperm DNA
damage and male subfertility.
Schagdarsurengin, U., & Steger, K. (2016). Epigenetics in male reproduction: effect of
paternal diet on sperm quality and offspring health. Nature Reviews Urology, 13(10), 584.

8. Sperm DNA Methylation:
 Unlike somatic cells which have hypermethlated DNA, germ
cells have hypomethylated DNA.
 The DNA methylation profile in testicular tissue showed
eightfold more hypomethylated gene loci relative to that of
somatic tissue.
 Hypermethylation in germ cells has been shown to affect
human male fertility.
Schagdarsurengin, U., & Steger, K. (2016). Epigenetics in male reproduction: effect of
paternal diet on sperm quality and offspring health. Nature Reviews Urology, 13(10), 584.

9. Sperm RNA:
 Sperm RNA can act as an epigenetic regulator.
 Spermatozoa are transcriptionally inactive cells, they contain
both mRNAs and noncoding RNAs (ncRNAs).
 Although sperm RNA is transmitted to the oocyte and
inhibition of sperm-delivered miRNAs (micro-RNA) results in
developmental delay in the zygote.
Schagdarsurengin, U., & Steger, K. (2016). Epigenetics in male reproduction: effect of
paternal diet on sperm quality and offspring health. Nature Reviews Urology, 13(10), 584.

10. Dietary Epigenetic Signature:
 Dietary compounds, especially phytochemicals, minerals and
vitamins, can effect changes in epigenetic signatures of
somatic as well as germ cells by influencing enzymes and
other proteins responsible for epigenetic modifications.
Schagdarsurengin, U., & Steger, K. (2016). Epigenetics in male reproduction: effect of
paternal diet on sperm quality and offspring health. Nature Reviews Urology, 13(10), 584.