Identification and functional characterization of solute carrier family 6 genes in Ciona savignyi

The solute carrier 6 (SLC6) gene family, functioning as neurotransmitter transporters, plays the crucial roles in neurotransmission, cellular and organismal homeostasis. In this study, we found an expansion of SLC6 family gene in the genome of chordate invertebrate Ciona savignyi. A total of 40 candidate genes including 29 complete and 11 putative genes were identified as SLC6 family gene homologs. Phylogenetic analysis revealed that most of these Ciona SLC6 genes were highly conserved with the vertebrate ones, although gene duplication and gene losses did exist. Four genes were selected from SLC6 subfamilies to be further investigated for their functional characteristics on cell growth and migration through overexpression approach in cultured cell lines. The results showed both SLC6A7 and SLC6A17 from amino acid transporters AA1 and AA2 sub-families, respectively, significantly suppressed the cell proliferation and migration. While SLC6A1 and SLC6A4, which were classified into GABA and monoamine transporters, respectively, did not affect the cell proliferation and migration in HEK293T, HeLa, and MCF7 cells. The whole set of C. savignyi SLC6 genes identified in this study provides an important genomic resource for future biochemical, physiological, and phylogenetic studies on SLC6 gene family. Our experimental data demonstrated that Ciona amino acid transporters, such as SLC6A7 and SLC6A17, were essential for cell physiology and behaviors, indicating their crucially potential roles in the control of cell proliferation and migration during ascidian embryogenesis.