However, whether BMP signals are involved in the maintenance of eye-field identity and/or specification of neural retina cells has not been determined.
These data suggest that lens-derived BMP signals are required for the maintenance of eye-field identity and the induction of neural retina cells.
Nevertheless, the molecular mechanisms that regulate the induction and maintenance of eye-field cells, and the specification of neural retina cells are poorly understood.
Our results provide evidence that at blastula stages, BMP signals inhibit the acquisition of eye-field character, but from neural tube/optic vesicle stages, BMP signals from the lens are crucial for the maintenance of eye-field character, inhibition of dorsal telencephalic cell identity and specification of neural retina cells.
The reason for the selection of these three stages is that essential developmental events occur in each stage: stage 20 sees the establishment of eye placodes, stage 25 sees eye vesicle closure and the onset of lens formation, and stage 30 sees the completion of eye development (though genes used for the growth and maintenance of eyes are still active).
Studies in Xenopus, zebrafish and medaka suggest that the Wnt-PCP pathway might be necessary during the formation and maintenance of the eye field, mediating morphogenetic movements.
In Xenopus, the Wnt-PCP signalling pathway is essential for the formation and maintenance of the eye field, mediating morphogenetic movements, as well as the crosstalk of intracellular ephrinB1 and PCP signalling that is required for retinal progenitors to move into the eye field (Lee et al., 2006).
Eye velocity sensitive neurons in FEF could be associated with roles in maintenance of steady-state eye velocity and gain control of SP (see Tanaka and Lisberger 2002; for reviews, see Nuding et al. 2008).
These miRNA clusters may reveal possible synergisms in the differentiation, cell-lineage commitment, development and maintenance of the analyzed eye structures.
Taken together, these data provide evidence that, until stage 13, maintenance of Rax2-positive eye-field identity and induction of neural retina cells requires signals from adjacent tissues.
