Organizer restriction through modulation of Bozozok stability by the E3 ubiquitin ligase Lnx-like

Authors:
Open Access
Publisher website
Google Scholar
Abstract
Ubiquitin-mediated degradation influences embryonic axis formation by regulating the stability of ventrally expressed transcription factors, although it is unclear whether dorsal factors are similarly modulated. In Zebrafish, the E3 ubiquitin ligase Lnx-l acts on the dorsal transcriptional repressor Boz to control dorso-ventral axis formation. The organizer anchors the primary embryonic axis, and balance between dorsal (organizer) and ventral domains is fundamental to body patterning. LNX (ligand of Numb protein-X) is a RING finger and four PDZ domain-containing E3 ubiquitin ligase1,2. LNX serves as a binding platform and may have a role in cell fate determination, but its in vivo functions are unknown1,2,3,4,5. Here we show that Lnx-l (Lnx-like) functions as a critical regulator of dorso-ventral axis formation in zebrafish. Depletion of Lnx-l using specific antisense morpholinos (MOs) caused strong embryonic dorsalization. We identified Bozozok (Boz, also known as Dharma or Nieuwkoid) as a binding partner and substrate of Lnx-l. Boz is a homeodomain-containing transcriptional repressor induced by canonical Wnt signalling that is critical for dorsal organizer formation6,7,8,9,10,11,12. Lnx-l induced K48-linked polyubiquitylation of Boz, leading to its proteasomal degradation in human 293T cells and in zebrafish embryos. Dorsalization induced by Boz overexpression was suppressed by raising the level of Lnx-l, but Lnx-l failed to counteract dorsalization caused by mutant Boz lacking a critical motif for Lnx-l binding. Furthermore, dorsalization induced by depletion of Lnx-l was alleviated by attenuation of Boz expression. We conclude that Lnx-l modulates Boz activity to prevent the invasion of ventral regions of the embryo by organizer tissue. These studies introduce a ubiquitin ligase, Lnx-l, as a balancing modulator of axial patterning in the zebrafish embryo.

This publication has 37 references indexed in Scilit: