Crucial role of phosphatidylinositol 4-kinase IIIα in development of zebrafish pectoral fin is linked to phosphoinositide 3-kinase and FGF signaling

Abstract

Phosphatidylinositol 4-kinases (PI4Ks) catalyze the first committed step in the synthesis of phosphoinositides, important lipid regulators of signaling and trafficking pathways. Here we cloned Pik4a, one of the zebrafish PI4K enzymes, and studied its role(s) in vertebrate development using morpholino oligonucleotide-based gene silencing in zebrafish. Downregulation of Pik4a led to multiple developmental abnormalities, affecting the brain, heart, trunk and most prominently causing loss of pectoral fins. Strikingly similar defects were caused by treatment of the developing embryos with the phosphoinositide 3-kinase (PI3K) inhibitor, LY294002. To investigate the cause of the pectoral fin developmental defect, we focused on fibroblast growth factor (FGF) signaling pathways because vertebrate limb development requires the concerted action of a series of FGF ligands. Using in situ hybridization, the pectoral fin defect was traced to disruption of the early FGF signaling loops that are crucial for the establishment of the sharp signaling center formed by the apical ectodermal ridge and the underlying mesenchyme. This, in turn caused a prominent loss of the induction of one of the mitogen-activated protein kinase (MAPK) phosphatases, Mkp3, an essential intermediate in vertebrate limb development. These changes were associated with impaired proliferation in the developing fin bud due to a loss of balance between the MAPK and PI3K branch of FGF-initiated signals. Our results identify Pik4a as an upstream partner of PI3Ks in the signaling cascade orchestrated by FGF receptors with a prominent role in forelimb development.

Mutations in Tetratricopeptide Repeat Domain 7A Result in a Severe Form of Very Early Onset Inflammatory Bowel Disease

“…Since TTC7A is required for proper localization of PI4KIIIα at the plasma membrane 24 , we propose that TTC7A mutations result in disease through loss of PI4KIIIα at the plasma membrane and subsequent reduction of PIP that is required for cell polarity and survival. In support of this model, down-regulation of PI4KIIIα results in increased apoptosis 25 , and furthermore intestinal specific murine knockout of Pi4kca (PI4KIIIα) results in a strikingly severe intestinal phenotype with widespread mucosal epithelial degeneration 26 reminiscent of our patients with TTC7A mutations. Therefore, our results demonstrate a direct interaction between PI4KIIIα-TTC7A.…”

Phosphoinositides: Tiny Lipids With Giant Impact on Cell Regulation

“…Morpholino-induced downregulation of PI4KA in zebrafish embryos caused massive and complex developmental defects especially affecting the brain and were characterized by lack of pectoral fins. This latter defect could be traced to impaired Fgf signaling and was phenocopied by PI 3-kinase inhibitors consistent with a decreased supply of PtdIns(4,5)P 2 at the PM (959). It is notable that PI4KA shows the highest expression in the brain both during development and in adult rodents (1107,1828).…”

Genetic and functional studies of phosphatidyl-inositol 4-kinase type IIIα

“…THAP7 is a histone tail-binding protein that represses transcription by recruiting the HDAC3 histone deacetylase to transcriptional complexes [41] and a close relationship between Fgf signaling and histone deacetylation has been documented [42, 43]. In this context it is notable that downregulation of PI4KIIIα in zebrafish embryos results in defective Fgf signaling [44]. However, it will require further studies to determine whether PI4KA haploinsufficiency contributes to some of the symptoms associated with 22q11.2 deletion syndromes.…”