The many dimensions of germline competence

Area of Science:

• Developmental Biology
• Stem Cell Biology
• Reproductive Biology

Background:

• Primordial germ cell (PGC) specification is crucial for germline development.
• Human and mouse PGC differentiation exhibit differences, with identified in vitro cell states for PGC-like cell (PGCLC) differentiation.
• The relationship between in vitro PGCLC competent states, embryonic development, and in vivo PGC origins remains debated.

Purpose of the Study:

• To review human PGCLC differentiation literature in comparison to mouse and non-human primate models.
• To re-evaluate the germline competence of human pluripotent stem cells (hPSCs).
• To explain paradoxical observations in hPGCLC origin and signaling requirements.

Main Methods:

• Literature review of human, mouse, and non-human primate PGCLC differentiation studies.
• Analysis of cell-cell interactions and signaling gradients in vitro.
• Conceptual framework development for germline competence.

Main Results:

• Human pluripotent stem cells (hPSCs) demonstrate significant germline competence, contrary to previous assumptions.
• Local cell interactions create endogenous signaling gradients that confound PGCLC differentiation assays.
• A single, unique germline competent state is unlikely; competence exists within a higher-dimensional cell state landscape.

Conclusions:

• Paradoxical findings in hPGCLC development may stem from local cellular environments and signaling.
• Germline competence is not a linear spectrum but a complex, multi-dimensional landscape of cell states.
• Revisiting models of PGC development considering cell interactions is essential.