We previously identified targets of Gata3 in CNCCs of 28 hpf zebrafish embryos using FACS to isolate cells positive for both fli1:EGFP and sox10:mRFP. We performed RNA-seq using cells isolated from gata3 morpholino-injected embryos, embryos transgenically overexpressing GATA3, and control embryos [19]. In this study, we used a similar approach to determine targets of Shh and genes co-regulated by Shh and Gata3. At 24 hpf, one group of zebrafish embryos was treated with a subteratogenic dose of the Shh antagonist cyclopamine, another was injected with a gata3 morpholino in addition to cyclopamine treatment, and a third group received only vehicle treatment as a control group. FACS and RNA-seq was performed on these embryos at 28 hpf.
To determine the effect of treatment and batch, we performed principal component analysis (PCA) across all six groups (Fig. 1). Embryos with loss-of-function treatments separated from overexpression and control embryos along PC1 (which explained 36.7% of the variance). Embryos from the overexpression group separated from controls along PC 2 (13.5% of the variance). PC 2 also separated the Shh loss-of-function and Gata3 loss-of-function groups, with the double loss-of-function group being intermediate (Fig. 1). Together, these results show that treatment was a major driver of variation in the dataset, while also indicating similarity in effects by disruption of Shh and Gata3 signaling. Finally, the lack of clustering across RNA-seq experiments and the tight clustering of the two separate control groups demonstrate that batch was not a major source of variation.
Despite the low dose, RNA-seq on cyclopamine-treated embryos identified 704 significantly differentially expressed genes (Fig. 2A), of which 351 were upregulated and 353 were downregulated. Gene Ontology (GO) analysis showed multiple important enriched signaling pathways (Fig. 2B). Hedgehog signaling was the most heavily affected, as expected. Notably, the Wnt signaling pathway was the next most highly enriched (Fig. 2B), similar to our previous findings with gata3 [19]. This suggests potential co-regulation of this pathway by Gata3 and Shh.
The transcriptome of embryos injected with gata3 morpholino and treated with cyclopamine consists of 429 significantly differentially expressed genes (Fig. 2C), of which 187 genes were upregulated and 242 were downregulated. Unlike the single-treatment experiments, the enriched pathways were primarily related to lipids. Connective tissue development was also enriched in our data (Fig. 2D). We performed RT-qPCR to validate our RNA-seq on the five most up- and down-regulated genes using the cyclopamine dataset. Eight out of ten showed significant differential expression in the expected direction, recapitulating our results (Fig. 3).
To elucidate the shared targets of both Gata3 and Shh, we looked at differentially regulated genes that were common to multiple experimental groups (Fig. 4). Our dose of cyclopamine does not result in craniofacial defects on its own, only when combined with gata3 loss of function. Therefore, we were particularly interested in the genes differentially regulated in both the gata3 and double-treatment groups (184 genes). Within that subset, 96 genes had a magnitude of expression change that was greater when exposed to both treatments compared to the single gata3 morpholino knockdown alone. Once again, we find Wnt signaling to be the most enriched term (Fig. 5). This gene set is enriched in pathways relating to cartilage and bone morphogenesis (Fig. 5), suggesting a possible mechanism for the phenotype.
To determine targets likely to be biologically relevant, we used the discovery platform DisGeNET (https://www.disgenet.org/home/) to identify those with published gene-disease associations [20]. We found ten genes with disease associations related to cleft palate, general craniofacial defects, and outcomes similar or related to HDR syndrome (Table 1), which serve as prime candidates for future characterization.
Table 1: Gene-disease associations of genes that originated from the “biological mirroring” group (same direction of differential expression, greater magnitude in double-treatment group).
Zebrafish gene
|
Human disease association
|
Evidence (PMID)
|
Log2FC (gata3)
|
Log2FC (double)
|
scfd1
|
“Profound craniofacial abnormality”
|
27851892
|
−0.26
|
−2.51
|
flrt3
|
Hypogonadotropic hypogonadism
|
23643382
|
0.41
|
0.83
|
f3b
|
Nephrotic Syndrome
|
17469034
|
0.49
|
0.98
|
srpx
|
Hypogonadotropic hypogonadism
|
11397871
|
0.56
|
1.12
|
tbx1
|
DiGeorge Syndrome
Cleft palate
|
23996541
30121012
|
0.58
|
1.16
|
lhfpl2
|
IgA glomerulonephritis
|
25133636
|
0.27
|
2.08
|
sh3pxd2b
|
Ter Haar Syndrome
Hearing impairment
Craniofacial abnormalities
|
30962481
21818352
19669234
|
0.29
|
1.44
|
twist2
|
Barber-Say Syndrome, macrostomia
|
29329175
|
0.75
|
1.50
|
tmco1
|
Cerebrofaciothoracic dysplasia
|
30556256
|
0.28
|
1.56
|
smarcb1b
|
Coffin-Siris Syndrome
|
25169651
|
0.27
|
2.97
|
col9a1
|
Stickler Syndrome, cleft palate
|
21421862
|
2.30
|
4.60
|
Table 2: Gene-disease associations of genes that were only differentially expressed in fish exposed to both treatments (gata3 MO and cyclopamine).
Zebrafish gene
|
Human disease association
|
Evidence (PMID)
|
Log2FC (double)
|
tgfb3
|
Loeys-Dietz syndrome
|
26184463
|
2.15
|
slitrk6
|
Sensorineural hearing loss
|
29551497
23543054
|
0.77
|
polr1a
|
Acrofacial dystosis
|
25913037
|
0.80
|
bbs10
|
Bardet-Biedl
syndrome syndrome
Severe renal disease
|
27659767
|
1.07
|
tfap2b
|
Char syndrome
|
30579973
|
1.14
|
alx1
|
Frontonasal dysplasia
Severe micropthalmia
|
23059813
|
1.87
|
fgf3
|
Labyrinthine aplasia, microtia, and microdontia
Oto-dental syndrome
|
21752681
17656375
|
1.18
|
Another group of interest comprises genes that were only differentially expressed in fish receiving both treatments (147 genes, Fig. 4). As they require disruption in both pathways for misregulation, these genes are prime candidates for synergism between Gata3 and Shh. GO analysis did not reveal any pathways that immediately suggested a mechanism of action for the phenotypic interactions. We used the same gene-disease association approach for the double-treatment group. Looking at only the top 100 genes by gene-disease association score on DisGeNET, we found seven genes (Table 2).
To find modules of co-regulated genes connected to Shh and Gata3, we performed weighted gene co-expression network analysis (WGCNA) on our 24 datasets, which yielded 10 modules (Fig. 6). The number of genes per module ranged from 32 to 1,858 genes with an average size of 571 genes. Moreover, there were 91 genes that did not share similar co-expression with the other genes in the network and were assigned to the gray module.
We next mapped treatment back to the modules to identify those related to combined loss of Shh signaling and Gata3 function. Using the Pearson correlation coefficient between module eigengenes and sample traits (treatment type and batch), we found one module of particular interest, Module 3, containing 37 genes. It had a coefficient of 0.87 in the Shh/Gata3 module, which would make it an especially promising module to identify co-targets and hub genes of these two pathways. GO analysis of this module shows multiple highly enriched biological processes and pathways, again including Wnt signaling. In this module, eight genes are concordantly upregulated in both the gata3 experiment and the Shh experiment, while five are concordantly downregulated in these groups (Table 3).
Table 3: Module 3 genes with concordant differential expression in Gata3 and Shh treatment groups.
Gene
|
Gata3 Log2FC
|
CyA Log2FC
|
Concordantly upregulated
|
fzd3a
|
1.08
|
0.46
|
fzd3b
|
1.34
|
0.29
|
prkcg
|
0.56
|
0.8
|
grem2b
|
0.34
|
1.63
|
nkx2.2a
|
0.58
|
1.28
|
gpc1a
|
3.31
|
0.26
|
fosl1a
|
1.77
|
0.33
|
fosl2l
|
0.98
|
0.59
|
Concordantly downregulated
|
roraa
|
−0.36
|
−0.64
|
daam1a
|
−0.35
|
−0.53
|
foxa2
|
−0.34
|
−0.47
|
sfrp2
|
−0.35
|
−1.41
|
celsr1a
|
−0.25
|
−0.9
|