Fig. 3

Choanocyte expression of vertebrate microvillar gene homologs. In E. muelleri, choanocyte expression of candidate microvillar genes was examined through differential expression analysis of HU-treated (i.e., choanocyte-absent) sponges relative to untreated (i.e., choanocyte-present), control sponges. Genes with significantly lower expression in HU-treated sponges (log FC < −1) are interpreted as having elevated expression levels in choanocytes of normal, untreated sponges. In contrast, in E. fluviatilis, choanocyte gene expression levels (RPKM) were determined by direct sequencing of isolated choanocytes and were compared to choanocyte-free cell fractions (summary of expression values is provided in Additional file 2: Supplemental Table 1)