Zebrafish enhancer trap line showing maternal and neural expression of kctd15a

Abstract

Potassium channel tetramerization domain containing proteins (KCTDs), which share a conserved BTB (Brica-brac, Tramtrack, Broad complex) domain at their N-terminus, are known to be involved in both developmental and neural processes. However, the developmental expression patterns and functional roles of most vertebrate KCTDs remain unknown. Using enhancer-trapping technology, we have identified a transgenic zebrafish line (ub49) where the vector insertion is in close proximity to kctd15a, and where transgenic marker (eGFP) expression closely reflects endogenous kctd15a expression. Both ub49 and kctd15a show strong maternal expression that suggests a functional role during epiboly and gastrulation. At later developmental stages, expression of eGFP in ub49 also shares the same spatiotemporal features as kctd15a in several neural tissues, including cranial placode precursors, retina, and different areas of the developing brain. In the retina, we observed eGFP labeling of the inner nuclear layer (INL), including a heterogenous population of amacrine cells, and both laminae of the inner plexiform layer (IPL). This expression pattern suggests that Kctd15a proteins have several contextdependent functional roles in both developmental and neural processes. The enhancer trap line, which is the first transgenic reporter of Kctd gene expression in vertebrates, also provides a novel tool to study kctd15a function in vivo.

Inhibition of neural crest formation by Kctd15 involves regulation of transcription factor AP-2

“…As mentioned above, Kctd1 interacts with AP-2 (32,33). Kctd15, which we have shown to inhibit NC development and affect Wnt signaling and AP-2 function, is regulated by FGF in Xenopus, and an enhancer trap line that mimics kctd15 expression in zebrafish has been described (43,44). Further, the KCTD15 gene is associated with obesity in whole-genome association studies (53,54), but no molecular basis for such a link has been reported.…”

“…It remains to be studied whether Kctd15 inhibits gene regulation by AP-2 in general or only in a certain context. Although the expression patterns of AP-2 and Kctd15 overlap in some regions, they show considerable differences (23,29,31,43,44), and thus not all AP-2 functions are likely to be affected by Kctd15.…”

Protein partners of KCTD proteins provide insights about their functional roles in cell differentiation and vertebrate development

“…On the other hand, the role of KCTD15 in human obesity may be associated with its ability to inhibit neural crest formation by interfering with Wnt/beta‐catenin signaling pathway upstream or in concert with β‐catenin . In zebrafish, the suppression of KCTD15 by morpholino technology leads to the expansion of the neural crest domain .…”

“…Dorsal depletion of kctd15 in Xenopus embryos leads to bent axes with reduced head structures, defective eyes and abnormal somites, while ventral depletion causes defects in ventral and caudal morphologies . The zebrafish paralogue of KCTD15 , kctd15a, shows strong maternal expression suggesting a functional role during epiboly and gastrulation . At later stages, expression of kctd15a was observed in several neural tissues, including cranial placode precursors, different areas of the developing brain as well as in distinct cell populations within the retina .…”

Genome-Wide Analysis of Facial Regionalization in Zebrafish

“…We found 6 of 9 predicted dorsal genes to be enriched in the dorsal mandibular and hyoid arches: cadherin11 (cdh11), pou3f3a and pou3f3b (homologs of mouse Pou3f3 with dorsal expression (Jeong et al, 2008)), cd248a, kctd15a (also see (Gharbi et al, 2012), and postnb ( Figure 2D). The other three genes were excluded from the dlx5a:GFP and hand2:GFP expression domains, as predicted, but they did not present typical "dorsal" expression patterns: sfrp2 showed dorsal-specific expression that failed to co-localize with dlx2a (likely dorsal arch mesoderm), rassf10a was largely confined to the surface ectoderm rather than arch CNCCs, and osr2 was expressed in only a few cells between the arches and the eye (Swartz et al, 2011).…”