A microarray screen for direct targets of Zic1 identifies an aquaporin gene, aqp-3b, expressed in the neural folds

The Zic1 transcription factor plays multiple roles during early development, for example, in patterning the early neural plate and formation of the neural crest, somites, and cerebellum. To identify direct downstream target genes of Zic1, a microarray screen was conducted in Xenopus laevis that identified 85 genes upregulated twofold or more. These include transcription factors, receptors, enzymes, proteins involved in retinoic acid signaling, and an aquaglyceroporin (aqp-3b), but surprisingly no genes known to be involved in cell proliferation. We show that both aqp-3 and aqp-3b were expressed in adult tissues, while during early embryonic development, only aqp-3b was transcribed. During neurula stages, aqp-3b was expressed specifically in the neural folds. This pattern of aqp-3b expression closely resembled that of NF-protocadherin (NFPC), which is involved in cell adhesion and neural tube closure. Aqp-3b may also be involved in neural tube closure, since mammalian Aqp-3 promotes cell migration and proliferation.