It is ectoderm that secretes protein during development of the neural tube (inside which the spinal cord will grow). Ectoderm is the start of a tissue that covers the body surfaces, in this case the neural tube.
What Does Spinal Cord Develop From Ectoderm, Mesoderm, Endoderm?
I think it comes from mesoderm, because somites come from that, and the somites create the spine