Regulation of UNC-130/FOXD-mediated mesodermal patterning in C. elegans

Abstract

Spatial polarity cues in animals are used repeatedly during development for many processes, including cell fate determination, cell migration, and axon guidance. In C. elegans, the body wall muscle extends the length of the animal in four distinct quadrants and generates an UNC-129/TGF-β-related signal that is much higher in the dorsal two muscle quadrants compared to their ventral counterparts. This pattern of unc-129 expression requires the activity of the proposed transcriptional repressor UNC-130/FOXD whose body wall muscle activity is restricted to the ventral two body wall muscle quadrants. To understand how these dorsal-ventral differences in UNC-130 activity are established and maintained, we have analyzed the regulation of unc-130 expression and the distribution of UNC-130 protein. We have identified widespread, cis-acting elements in the unc-130 promoter that function to positively regulate ventral body wall muscle expression and negatively regulate dorsal body wall muscle expression. We have defined the temporal distribution of UNC-130 protein in body wall muscle cells during embryogenesis, demonstrated that this pattern is required to establish the dorsal-ventral polarity of UNC-129/TGF-β, and shown that UNC-130 is not required post-embryonically to maintain the asymmetry of body wall muscle unc-129 expression. Finally, we have tested the impact of the depletion of a variety of transcription factors, repressors, and signaling molecules to identify additional regulators of body wall muscle UNC-130 polarity. Our results confirm and extend earlier studies to clarify the mechanisms by which UNC-130 is controlled and affects the pattern of unc-129 expression in body wall muscle. These results further our understanding of the transcriptional logic behind the generation of polarity cues involving this poorly understood subclass of Forkhead factors.

The forkhead transcription factor UNC-130/FOXD integrates both BMP and Notch signaling to regulate dorsoventral patterning of the C. elegans postembryonic mesoderm

“…Unlike unc-130 , a well characterized and stably integrated unc-129p∷GFP transcriptional reporter Punc-129(4.2 Kb)∷gfp , which has 4.2 Kb sequences upstream of the translational start site of unc-129 driving the expression of GFP, shows robust expression in the dorsal embryonically-derived BWMs as previously reported (Kersey et al, 2016; Nash et al, 2000), but is not expressed in the M lineage (Figure 2H-N). Thus, unc-130, but not unc-129, is asymmetrically expressed in the ventral M lineage.…”

“…Previous studies have shown that unc-130 is expressed in the ventral bodywall muscles (BWMs) to restrict the expression of UNC-129/TGFβ to the dorsal BWMs for proper neuronal axon migration (Colavita et al, 1998; Kersey et al, 2016; Nash et al, 2000). The postembryonic mesodermal M lineage also exhibits distinct dorsoventral asymmetry (Figure 1).…”

“…One of them has a stably integrated transgenic UNC-130∷GFP translational reporter evIs120[unc-130p∷unc-130∷GFP] that was generated using an extra chromosomal array (Nash et al, 2000), and will be designated as UNC-130∷GFP(OE). Another strain, unc-130(gv45)[unc-130∷superGFP] , has the endogenous UNC-130 tagged with a superfolder GFP via CRISPR (Kersey et al, 2016), and will be designated as UNC-130∷superGFP. We generated strains expressing UNC-130∷GFP(OE) or UNC-130∷superGFP along with an integrated hlh-8p∷NLS∷mCherry∷lacZ reporter that specifically marks the M lineage, and found both strains exhibited the same GFP expression pattern in the M lineage, which is summarized in Figure 2.…”

“…FoxD3 has also been shown to function as a transcriptional repressor to regulate Nodal expression and mesoderm induction (Steiner et al, 2006; Yaklichkin et al, 2007). In C. elegans embryonic body wall muscles, UNC-130 functions to repress the expression of a TGFβ-like molecule UNC-129 to regulate axon guidance (Kersey et al, 2016; Nash et al, 2000). UNC-130 can also repress the expression of the Notch ligand LAG-2 in the IL2 neurons during reproductive development (Ouellet et al, 2008).…”

“…The resulting dorsal-ventral gradient of UNC-129/TGFβ regulates neuronal axon migration (Colavita and Culotti, 1998; Colavita et al, 1998). The ventral BWM-specific expression of unc-130 appears to be a result of both positive and negative regulatory inputs exerted by multiple transcription factors (Kersey et al, 2016).…”