Expression of epithelial and synaptic gene homologs. Interaction network of epithelial (A) and synaptic (C) genes showing homologs that are present in the A. queenslandica genome (blue circles). Genes with related functions are indicated by dotted circles. Sponge genes were retrieved by matching Aqu1 gene models to previously published sequences [23, 69]. Protein interactions were obtained from STRING  and displayed using Cytoscape . Relative expression of epithelial (B) and synaptic (D) gene homologs in the four developmental stages (red, high; blue, low; gray, no sponge homolog). Stage enrichment of genes was estimated using Fisher’s exact test (p-values shown).