Functional Analyses of Histone Methyltransferases in Sea Lamprey Embryos Undergoing Programmed DNA Elimination

Area of Science:

• Developmental Biology
• Epigenetics
• Genomics

Background:

• Sea lampreys exhibit programmed genome rearrangement during embryogenesis.
• Specific chromosomes are eliminated from somatic cells, silencing associated genes.
• Epigenetic silencing marks, like H3K9me3 and H4K20me3, are found on eliminated chromosomes.

Purpose of the Study:

• To investigate the role of sea lamprey histone methyltransferases in depositing silencing marks on eliminated DNA.
• To determine if these epigenetic marks are essential for programmed DNA elimination.
• To assess the broader impact of these methyltransferases on early sea lamprey development.

Main Methods:

• Cas9 gene editing was used to create knockout embryos for four histone methyltransferases.
• Lightsheet imaging was employed to visualize developmental processes.
• RNA sequencing was performed to analyze gene expression changes.

Main Results:

• Knockout embryos showed reduced deposition of repressive histone marks on eliminated DNA (micronuclei).
• These histone methyltransferases were not essential for the programmed DNA elimination process.
• The marks appear to contribute to interim silencing of germline-specific chromosomes.
• Significant impacts on post-blastula survival and development were observed in knockout embryos.

Conclusions:

• Sea lamprey histone methyltransferases contribute to epigenetic silencing on eliminated chromatin.
• While not essential for DNA elimination, these marks play a role in interim silencing and overall development.
• Further research is needed to fully elucidate the complex mechanisms of genome reprogramming and its developmental consequences.