HEK-293 T cells were transfected with different Y-P30-GFP constructs and co-cultured with cortical primary neurons. Of the constructs tested, SP-Y-P30-GFP has been shown in Figure 2 to deliver a protein detectable in the culture supernatant. However, the peptide is not taken up into neurons. White arrows point to MAP-2 immunoreactive neurons (blue in the merged picture), purple arrows to transfected HEK-293 T cells (green or red + green in the merged pictures). Scale bar is 20 μm.