Visceral endoderm function is regulated by quaking and required for vascular development

The quaking (qkl) gene produces three major alternatively spliced variants (qkl-5, -6, -7) that encode for proteins that share the RNA binding, KH domain. Previous studies utilizing the qk^k2 allele, which contains an N-ethyl-N-nitrosourea (ENU)-induced point mutation in the KH domain, demonstrate that this functional region of qkl is required for embryonic vascular development. In the current studies we demonstrate that qk^l-1/qk ^l-1 mutants, which lack the QKI-5 splice variant, also died at midgesiation due to vascular remodeling defects, in addition, although all three QKI isoforms were expressed in the visceral endoderm of wildtype yolk sacs, qkl-6 and qkl-7 transcript and protein expression were suppressed in qk ^k2/qk^k2 and qk^l-1/qk^l-1 mutant yolk sacs, suggesting that the KH-domain of QKI-5 was required for qkl-6 and qkl-7 expression. Further studies revealed that the cellular role of qkl is to regulate visceral endoderm function, including the local synthesis of retinoic acid (RA) and the subsequent control of endothelial cell proliferation, matrix production, and visceral endoderm survival. Although these defects were rescued by exogenous RA, visceral endoderm function or vascular remodeling were not restored. Thus, we conclude that qkl regulates visceral endoderm function, which is critical for vascular remodeling.