The new brain science indicates that brain maturation is going on much later in development than people had thought, so there is some reason, perhaps, to say that 17-year-olds are not the same as adults.
This occurs because although the sex of a developing embryo is determined at conception (in humans, as in other mammals, due to the presence of an X or Y chromosome in the sperm), this sex does not become phenotypically manifested until much later in development.
Because the fusions are revealed much later in development, we cannot completely exclude other scenarios.
In fact, in wild-type embryos, Cyclin B is not upregulated until much later in development after gonad coalescence (Asaoka et al. 1999).
Whereas somatic nuclei turn on transcription, it is shut down in PGCs, and they remain transcriptionally quiescent until after they exit the gut much later in development (Zalokar 1976; Seydoux and Dunn 1997).
Additionally, we show that early zebrafish embryos do have the potential to generate cells that express the typical osteoclast markers Trap and cathepsinK, which are normally only found much later in development (Hammond and Schulte-Merker, 2009).
Nevertheless, it is notable that the same pattern, decreased ChAT without a change in HC3 binding, is seen at the same early stage after neonatal chlorpyrifos treatment (Dam et al. 1999), and deficits in HC3 binding do not emerge until much later in development (Slotkin et al. 2001).
Scale bars: 10 µm (A – C ), (E – G ), 100 µm (D and H ). DOI: http://dx.doi.org/10.7554/eLife.02443.012 To independently address the extend of DNA damage accumulation in His C mutant embryos, we used TUNEL assays which support that His C mutant cells do not accumulate significant levels of DNA damage until much later in development (≥10 hr AEL) when these embryos die.
