Lnx2b, an E3 ubiquitin ligase, in dorsal forerunner cells and Kupffer's vesicle is required for specification of zebrafish left–right laterality

Abstract

The establishment of left–right (LR) axis in zebrafish embryos relies on numerous genes expressed in the cluster of dorsal forerunner cells (DFCs) that form Kupffer's vesicle (KV), the transient cilia-rich organ with functional similarity to mouse node in the case of LR axis determination. Even though several genes in the DFCs and KV have been identified to be implicated in LR body patterning so far, the underlying regulatory mechanisms in particular dependent upon ubiquitin (Ub)– proteasome system have not yet been identified. In this study, we report that Lnx2b, a RING domain containing E3 Ub ligase, specifically expressed in migratory DFCs and developing KV, plays a critical role in the establishment of LR laterality. Depletion of Lnx2b using antisense morpholino oligonucleotides (MOs) inhibited the left-side biased expression of southpaw and resulted in the randomization of the heart jogging and looping in zebrafish embryos. A DFCs-specific Lnx2b loss of function approach showed that the randomization of LR patterning caused by the depletion of Lnx2b was not simply due to the early dorsoventral body patterning defects or the MO toxicity, but the loss of its function in the DFCs and KV. Collectively, our data showed that Lnx2b is the first analyzed E3 Ub ligase, which is involved in LR laterality during zebrafish embryogenesis.