My two questions that I would like to investigate as a developmental biologist are:

1. To what degree do parental epigenetic marks influence the epigenome of their developing offspring? Are epigenetic marks hereditary, or are they generated de novo in the embryo?

2. What are the physiological/cellular factors that influence the dynamics and position of methylation and histone modification during development?

Reflection:

I find it very interesting to go back to the very beginning of the course and see how much my thinking surrounding and understanding of developmental biology has changed!

We have definitely answered the first question over the course of the semester. The first wave of global demethylation occurs in the developing primordial germ cells (PGCs), and de novo methylation is carried out by DNMT3A and 3B, with the help of DNMT3L. DNMT1 is responsible for the maintenance of parental methylation, and does so by targeting hemimethylated strands of DNA. The second wave occurs during early embryogenesis and assists with the establishment of pluripotency in cells. In spite of this, the methylation state of imprinted genes is preserved throughout the process.

As for the second question, this is a huge question and not one that could be completely answered throughout the course. I actually think that a better question to ask would be the opposite: how do methylation and histones affect development? I have learned that the methylation state, chromatin conformation (euchromatin vs. heterochromatin), and histone modifications (repressive, activating, or bivalent) greatly alter the cells’ potential cell fates and levels of gene expression.

Some learning objectives I demonstrated with this assignment:

• Approach questions, concepts, and facts with curiosity
• Assess your own level of knowledge in a field or area of interest and identify “gaps” in your knowledge or skills
• Identify and ask informative questions so as to “extract” useful information from other people’s knowledge and from experiments
• Distinguish questions that can be investigated experimentally from questions that cannot