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In the Materials and Methods section, the service providers for in vitro Cas9 assay and Illumina Sequencing systems were not mentioned.

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The forebrain roof plate undergoes dramatic morphogenetic changes to invaginate, and this leads to formation of the two cerebral hemispheres. While many genetic factors are known to regulate this process, the mechanism of forebrain roof plate invagination remains unknown. In a recent study we have identified retinoic acid as a signal from the dorsal mesenchyme that regulates the invagination of the roof plate. This has brought into focus the importance of the interaction between the dorsal mesenchyme and the underlying roof plate. One of the structures derived from the dorso-medial forebrain after roof plate invagination is the hippocampus. While the functions of the hippocampus are conserved between birds and mammals, there are distinct structural differences. We have studied hippocampus development in the chick embryo and uncovered several similarities and differences between the process in mammals and birds. This study has also lent support to one of the prevalent models of structural homology between the avian and mammalian hippocampus. In this review, we have underscored the importance of the chick embryo as a model for studying forebrain roof plate morphogenesis and hippocampus development.

Information from the retina is carried along the visual pathway with accuracy and spatial conservation as a result of topographically mapped axonal connections. The optic tectum in the midbrain is the primary region to which retinal ganglion cells project their axons in the chick. The two primary axes of the retina project independently onto the tectum using different sets of guidance cues to give rise to the retinotectal map. Specificity of the map is determined by attractive or repulsive interactions between molecular tags that are distributed in gradients in the retina and the tectum. Despite several studies, knowledge of the retinotectal guidance molecules is far from being complete. We screened for all molecules that are expressed differentially along the anterior-posterior and medial-lateral axes of the chick tectum using microarray based transcriptional profiling and identified several novel candidate retinotectal guidance molecules. Two such genes, encoding Wnt5a and Raldh2, the synthesizing enzymes for retinoic acid, were further analyzed for their function as putative regulators of retinotectal map formation. Wnt5a and retinoic acid were found to exhibit differential effects on the growth of axons from retinal explants derived from different quadrants of the retina. This screen also yielded a large number of genes expressed in a lamina-specific manner in the tectum, which may have other roles in tectal development. J. Comp. Neurol. 525:459-477, 2017. © 2016 Wiley Periodicals, Inc.