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Evolution of predetermined germ cells in vertebrate embryos: implications for macroevolution.
Andrew D Johnson1, Matthew Drum, Rosemary F Bachvarova
1Division of Genetics, University of Nottingham, Queen's Medical Centre, Nottingham NG7 2UH, UK. andrew.d.johnson@nottingham.ac.uk
Evolution & Development
|June 26, 2003
Summary
Regulative germ cell determination, where signals induce primordial germ cells (PGCs), is ancestral in tetrapods. Predetermined PGCs, established by germ plasm, evolved independently multiple times in vertebrates.
Area of Science:
- Developmental Biology
- Evolutionary Biology
- Comparative Embryology
Background:
- The germ line, essential for reproduction, originates from primordial germ cells (PGCs) during embryonic development.
- Two primary modes of PGC determination exist: germ plasm-mediated predetermination and signal-induced regulative determination.
- Distinct mechanisms of germ cell determination are observed in major amphibian lineages (anurans vs. urodeles).
Purpose of the Study:
- To ascertain the ancestral mechanism of germ cell determination in the tetrapod lineage.
- To investigate the evolutionary patterns of germ cell determination in higher vertebrates.
- To understand the role of PGC determination as a developmental constraint.
Main Methods:
- Phylogenetic analysis of morphological processes across amphibian groups.
- Correlation of embryological traits with germ cell determination mechanisms.
- Comparative study of anuran and urodele amphibians.
Main Results:
- Regulative germ cell determination is associated with ancestral embryological processes.
- Predetermined germ cells correlate with derived morphological traits.
- Germ plasm appears to have evolved independently in multiple vertebrate lineages.
Conclusions:
- Regulative germ cell formation acts as a significant developmental constraint in vertebrate embryos prior to the pharyngula stage.
- The ancestral tetrapod mechanism for germ cell determination is likely regulative.
- Independent evolution of germ plasm is a recurring theme in vertebrate germ line development.