Seeing is believing – watching eyes take shape
Despite looking nothing like brain tissue, our eyes initially form as outgrowths from the brain
during embryonic development. New research from Kenzo Ivanovitch, Florencia Cavodeassi and
Stephen Wilson has revealed how prospective eye cells initiate their journey from the brain to the
eye sockets. They reasoned that two criteria must be met for successful outgrowth of the eyes:
first, eye forming cells must initiate a behavioural programme distinct from adjacent territories in
the brain; and second, that future eye cells must not intermix with other brain cells. To investigate
these issues, the UCL researchers used very high-resolution microscopy to resolve the behaviours
of individual eye forming cells in transparent zebrafish embryos that are eminently well-suited for
such imaging analyses. They discovered that the eye-forming cells precociously organise as a
polarised sheet of cells (an epithelium) when compared to cells in neighbouring brain regions, and
that this behaviour is essential for the proper evagination of the primordia of the eyes. They further
unravelled a molecular mechanism that ensures that the eye-forming cells are prevented from
intermixing with adjacent brain cells as the eyes begin to take shape. This work is paving the way
for a better understanding of eye morphogenesis and organogenesis and is published in papers in
the journals Development and Developmental Cell.
Figure 1. Image of a head-on view of the brain of a zebrafish embryo just as the prospective eye cells (green) start to push out laterally to form the optic vesicles. The orange labelling is Laminin, a protein present at the outer surface of the eye cells that is necessary for proper outgrowth.
Figure 2. Sequential images from a movie in which prospective eye cells (green) reorganise and move outwards from the brain to form the nascent eyes (optic vesicles).
Movie 1. Time-lapse movie of prospective eye cells bulging out from the brain (including telencephalon and hypothalamus) to form the nascent eyes (optic vesicles). The membranes of the cells are labelled green and the cell nuclei in red.
Cavodeassi, Ivanovitch and Wilson (2013). Eph/Ephrin signalling maintains eye field segregation from adjacent neural plate territories during forebrain morphogenesis. Development, 140:4193-202.
Ivanovitch, Cavodeassi and Wilson (2013). Precocious acquisition of neuroepithelial character in the eye field underlies the onset of eye morphogenesis. Developmental Cell, 27:293-305.