Updated project metadata. Eyes absent homolog 3 (EYA3) is a transcriptional cofactor that is known to partner with the sine oculis homeobox (SIX) family to regulate gene expression. In this study, we characterized a novel splice isoform of EYA3, including the alternative cassette exon 7 (EYA3+ex7), that becomes more highly expressed compared to the isoform lacking exon 7 (EYA3Δex7) during muscle cell differentiation and muscle development. This developmentally-regulated splicing pattern was evolutionarily conserved in humans, mice, rats, chickens, and zebrafish. We found that EYA3 isoforms are vital to proliferation and differentiation of myoblasts in a cell culture model of myogenesis. To understand the underlying mechanism, we defined the transcriptional networks controlled by EYA3 through RNA-sequencing of EYA3 depleted cells. We then hypothesized that binding partners of EYA3+ex7 and EYA3Δex7 might contribute to the mechanism by which they regulate transcription. An affinity-purification mass spectrometry approach was used to identify binding partners of EYA3 isoforms by heterologous expression of hemagglutinin (HA) tagged isoforms in HEK293T cells. 26 binding partners (defined as those with log2(FC) > 1 and p < 0.05 compared to HA epitope tag control) were shared among the EYA3 isoforms, including five transcription factors: zinc finger and BTB domain containing 1 (ZBTB1), tumor protein p53 (TP53), SIX5, SIX2, and SIX4. We next demonstrated that ZBTB1 and SIX4 share overlapping transcriptional targets with EYA3, indicating that EYA3 partners with ZBTB1 or SIX4 to regulate gene expression. Three and thirteen unique binding partners were discovered for EYA3Δex7 and EYA3+ex7, respectively. Therefore, inclusion of Eya3 exon 7 may allow for unique interactions and contribute to functions of EYA3+ex7 that are distinct from EYA3Δex7. This dataset includes affinity purified data for Eya3 isoforms in HEK293T cells.