dmrt2 and myf5 Link Early Somitogenesis to Left-Right Axis Determination in Xenopus laevis

Abstract

The vertebrate left-right axis is specified during neurulation by events occurring in a transient ciliated epithelium termed left-right organizer (LRO), which is made up of two distinct cell types. In the axial midline, central LRO (cLRO) cells project motile monocilia and generate a leftward fluid flow, which represents the mechanism of symmetry breakage. This directional fluid flow is perceived by laterally positioned sensory LRO (sLRO) cells, which harbor non-motile cilia. In sLRO cells on the left side, flow-induced signaling triggers post-transcriptional repression of the multi-pathway antagonist dand5. Subsequently, the co-expressed Tgf-β growth factor Nodal1 is released from Dand5-mediated repression to induce left-sided gene expression. Interestingly, Xenopus sLRO cells have somitic fate, suggesting a connection between LR determination and somitogenesis. Here, we show that doublesex and mab3-related transcription factor 2 (Dmrt2), known to be involved in vertebrate somitogenesis, is required for LRO ciliogenesis and sLRO specification. In dmrt2 morphants, misexpression of the myogenic transcription factors tbx6 and myf5 at early gastrula stages preceded the misspecification of sLRO cells at neurula stages. myf5 morphant tadpoles also showed LR defects due to a failure of sLRO development. The gain of myf5 function reintroduced sLRO cells in dmrt2 morphants, demonstrating that paraxial patterning and somitogenesis are functionally linked to LR axis formation in Xenopus.

FGF-mediated establishment of left-right asymmetry requires Rab7 function in the dorsal mesoderm in Xenopus

“…Therefore, we analyzed the somitogenic factor myf5 during gastrulation, which showed strong reductions under these conditions, indicating a high sensitivity of the paraxial tissues to a loss of Rab7 (Figures 2H-J). This strong inhibition of myf5, which has been implicated in LR symmetry breakage very recently (Tingler et al, 2022), suggested a potential impact on LRO sensor specification as well. Thus we wondered whether sLRO cells were specified correctly, i.e., expressed characteristic marker genes (Figure 2A).…”

“…This correlates with the initial observation of Amaya and colleagues, who described exactly this paraxial sensitivity when using a dn-fgfr1 construct ( Amaya et al, 1993 ). Importantly, very recently Myf5 has been demonstrated to be required for LRO sensor formation in Xenopus , directly linking somitogenesis to LR asymmetry ( Tingler et al, 2022 ). Thus, inhibition of myf5 is sufficient to explain the LR defects obtained by loss of Rab7.…”

Esrrγa regulates nephron and ciliary development by controlling prostaglandin synthesis

“…Next, we designed genetic interaction studies to explore the relationship between esrrγa and ppargc1a . Suboptimal morpholinos (SOMOs) have been a consistent and well-established strategy to test whether multiple genes operate synergistically in a pathway in multiple species, including zebrafish and Xenopus laevis ( Chambers et al, 2020b ; Choi et al, 2015 ; DiBella et al, 2009 ; Epting et al, 2022 ; Fowler et al, 2021 ; Janssens et al, 2013 ; Kallakuri et al, 2015 ; Lefkopoulos et al, 2020 ; Lu et al, 2021 ; Maerker et al, 2021 ; Tingler et al, 2022 ; Wagle et al, 2011 ). Therefore, we injected SOMO doses of both esrrγa and ppargc1a , based on previously published doses ( Chambers et al, 2018 , 2020b ).…”