Figure 1.
Lymphocyte lineages in jawless and jawed vertebrates (based in part on Supp Fig 6 in ref [31]. Transcription factors required for T cell precursors (yellow), γδ/VLRC T cells (green), αβ/VLRA T cells (red), and Ig/VLRB cells (blue) are shown at left, in a hypothetical vertebrate ancestor. The authors suggested that the transcriptional control of multiple lymphocyte lineages predated the emergence of any antigen receptors. Enzymes required for generation of the different antigen receptors are shown at right.