Dvr1 transfers left–right asymmetric signals from Kupffer's vesicle to lateral plate mesoderm in zebrafish

Abstract

An early step in establishing left-right (LR) symmetry in zebrafish is the generation of asymmetric fluid flow by Kupffer’s vesicle (KV). As a result of fluid flow, a signal is generated and propagated from the KV to the left lateral plate mesoderm, activating a transcriptional response of Nodal expression in the left lateral plate mesoderm (LPM). The mechanisms and molecules that aid in this transfer of information from the KV to the left LPM are still not clear. Here we provide several lines of evidence demonstrating a role for a member of the TGFβ family member, Dvr1, a zebrafish Vg1 ortholog. Dvr1 is expressed bilaterally between the KV and the LPM. Knockdown of Dvr1 by morpholino causes dramatically reduced or absent expression of southpaw (spaw, a Nodal homolog), in LPM, and corresponding loss of downstream Lefty (lft1 and lft) expression, and aberrant brain and heart LR patterning. Dvr1 morphant embryos have normal KV morphology and function, normal expression of southpaw (spaw) and charon (cha) in the peri-KV region and normal expression of a variety of LPM markers in LPM. Additionally, Dvr1 knockdown does not alter the capability of LPM to respond to signals that initiate and propagate spaw expression. Co-injection experiments in Xenopus and zebrafish indicate that Dvr1 and Spaw can enhance each other’s ability to activate the Nodal response pathway and co-immunoprecipitation experiments reveal differential relationships among activators and inhibitors in this pathway. These results indicate that Dvr1 is responsible for enabling the transfer of a left-right signal from KV to the LPM.

Conserved regulation of Nodal-mediated left-right patterning in zebrafish and mouse

“…We performed co-immunoprecipitation experiments by co-expressing vg1-Flag with spaw-HA, or squint-HA as a positive control (Montague and Schier, 2017). In contrast to previous studies (Peterson et al, 2013), an interaction was detected between Vg1 and Spaw ( Fig. 2D), indicating that Vg1 and Spaw form heterodimers.…”

“…Nodal-Gdf1 heterodimers pattern the mouse left-right axis (Tanaka et al, 2007). Consistent with Gdf1 mutant phenotypes, knockdown of zebrafish vg1/gdf3 causes a reduction or absence of spaw in the LPM and heart looping phenotypes (Peterson et al, 2013), and rescue experiments of maternal-zygotic vg1 mutants suggest that Spaw requires Vg1 to pattern the left-right axis (Pelliccia et al, 2017). However, in contrast to mouse Nodal-Gdf1, Spaw-Vg1 heterodimers have not been detected in zebrafish (Peterson et al, 2013).…”

Correlated expression of retrocopies and parental genes in zebrafish

“…Only four of these retrocopies (ENSDARG00000089553 (Siddiqui et al 2010), ENSDARG00000037995 Peterson et al 2013), ENSDARG00000079355 (Thisse et al 2008) and ENSDARG00000011724 (Thisse and Thisse 2004)) have been described in publications.…”

Salient features of the ciliated organ of asymmetry

“…Intracellular Ca 2+ communication in the left endoderm could function to facilitate efficient extracellular transfer of secreted Nodal protein to the LPM. Alternatively, differential Ca 2+ levels may influence modulators of nodal signaling, such as Gdf1, 82 Dvr1 83 or Cerl2. 41 Uncovering mechanisms and pathways downstream of asymmetric Ca 2+ flux is an exciting area of investigation that is likely to provide new insight into the function of the ciliated organ of asymmetry.…”