Vg1 and regional specification in vertebrates: a new role for an old molecule

The Vg1 protein was discovered some ten years ago in a screen for localized maternal RNA molecules involved in early embryonic patterning in the frog Xenopus laevis. The localization of this molecule to the vegetal pole suggested that Vg1 might function as a determinant of embryonic cell fate, and its DNA sequence revealed that it is related to factors involved in induction of the mesoderm. However, it is only in the past year that evidence hinting at the role of Vg1 in early development has emerged. It now seems that although the key component for specifying a vertebrate dorsal axis has been known to us for a decade, cryptic processing pathways have kept its role in this important process hidden from view.