Abstract
Wnt signaling regulates multiple aspects of vertebrate central nervous system (CNS) development, including neurogenesis. However, vertebrate genomes can contain up to 25 Wnt genes, the functions of which are poorly characterized partly due to redundancy in their expression. To identify candidate Wnt genes as candidate mediators of pathway activity in specific brain progenitor zones, we have performed a comprehensive expression analysis at three different stages during zebrafish development. Antisense RNA probes for 21 Wnt genes were generated from existing and newly synthesized cDNA clones and used for in situ hybridization on whole embryos and dissected brains. As in other species, we found that Wnt expression patterns in the embryonic zebrafish CNS are complex and often redundant. We observed that progenitor zones in the telencephalon, dorsal diencephalon, hypothalamus, midbrain, midbrain-hindbrain boundary, cerebellum and retina all express multiple Wnt genes. Our data identify 12 specific ligands that can now be tested using loss-of-function approaches.
Highlights
Wnt/β-Catenin signaling is known to act in multiple ways to regulate vertebrate central nervous system (CNS) development, including as a mitogen [1], and in neural specification and differentiation [2,3,4]
At 48 and 72 hpf, we focused on known progenitor zones including the telencephalic pallium/subpallium [13], the dorsal diencephalon, the ventral diencephalon, the midbrain [15], the midbrain/hindbrain boundary [16], the cerebellum [17], and the ciliary marginal zone (CMZ) of the retina [18]
Our data clearly demonstrate the coincident expression of multiple Wnt genes in progenitor zones of the developing CNS (Fig 5F–5H and Table 2), and support previous observations of gene redundancy
Summary
Wnt/β-Catenin signaling is known to act in multiple ways to regulate vertebrate central nervous system (CNS) development, including as a mitogen [1], and in neural specification and differentiation [2,3,4]. The pathway functions in post-embryonic neurogenesis, to promote the differentiation of neural progenitor cells in the dentate gyrus of the hippocampus [5], the rostral migratory stream [6], and the hypothalamus [4]. With a few exceptions such as wnt7a in the dentate gyrus [7], it has been difficult to link functions in defined neural progenitor populations to specific Wnt ligands, possibly due to extensive redundancy within the Wnt family [8, 9]. In addition different Wnt ligands can activate multiple downstream pathways in the same tissue, such as in the zebrafish fin where wnt10a and wnt5b are both required for regeneration through ß-catenin-dependent and independent signaling, respectively [10] It is PLOS ONE | DOI:10.1371/journal.pone.0145810 December 29, 2015
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