Ancestral Stem Cell Reprogramming Genes Active in Hemichordate Regeneration

Area of Science:

• Developmental Biology
• Regenerative Medicine
• Evolutionary Biology

Background:

• Hemichordate worms exhibit remarkable regeneration capabilities, similar to planaria and hydra.
• Hemichordates are phylogenetically basal deuterostomes, potentially offering insights into early deuterostome body plan evolution.
• Extensive regeneration is uncommon in more derived deuterostomes, including chordates, mammals, and humans.

Purpose of the Study:

• To investigate if hemichordates employ functional homologs of canonical Yamanaka stem cell reprogramming factors (Oct4, Sox2, Nanog, Klf4) during regeneration.
• To compare the regenerative mechanisms of hemichordates with those of chordates, where these factors are not typically expressed during regeneration.

Main Methods:

• Identified potential hemichordate homologs of Yamanaka factors (Oct4, Sox2, Nanog, Klf4) from Ptychodera flava EST libraries: Pf-Pou3, Pf-SoxB1, Pf-Msxlx, and Pf-Klf1/2/4.
• Utilized in situ hybridization to analyze the expression patterns of these homologs during head regeneration in hemichordates.
• Performed functional assays by testing if Pf-Pou3 could rescue Oct4-deficient mouse embryonic stem cells, assessing pluripotency gene expression.

Main Results:

• Identified and characterized hemichordate homologs of Oct4, Sox2, Nanog, and Klf4.
• Demonstrated distinct expression patterns of these homologs during hemichordate head regeneration.
• Showed that Pf-Pou3 could partially maintain pluripotency gene expression in mouse embryonic stem cells lacking Oct4.

Conclusions:

• Hemichordates may utilize reprogramming factors for extensive regeneration, or chordates might have lost this capability.
• The conserved pluripotency gene circuits are intact in mammals and could potentially be reactivated for regeneration under specific regulatory signals.