Microbiology - Perspectives on plague

Several decades of work in frogs and fish led to the hypothesis that ‘localized determinants’ deposited in the egg by the mother establish the dorsal axis of the developing embryo, but the nature of the determinants has remained a mystery. New work in the zebrafish embryo identifies Squint, a Nodal-related transforming growth factor-β signal, as a possible localized dorsal determinant. Squint is present in the two- and four-cell embryo, suggesting that embryonic polarity is established very early on in development. The presence of Squint element in mammals suggests that this mechanism of polarity determination is conserved in the higher vertebrates.