RTK Classes in Mammals and C. elegans
| Class[i] | RTKs in mammals | Orthologs in C. elegans |
| I | EGFR, ERBB (4 known) | LET-23 |
| II | insulin receptor, IGF1-R | DAF-2 |
| III (5 Ig)[ii] | PDGFRs, CSF1R, KIT, FLT3 | none |
| IV (3 Ig) | FGF receptors (4 known) | EGL-15 |
| V (7 Ig) | VEGF receptors (3 known) | discussed here |
| VI | MET/HGFR, RON, SEA | F11E6.8 (discussed here) |
| VII (2 Ig) | TRK/NGFRs (3 known), ROR | KIN-8/CAM-1 |
| VIII (1 Ig) | ephrin receptors (14 known) | VAB-1 |
| IX | GDNF/NTN receptor (RET) | none |
| X (2 Ig) | TIE1, TIE2 | none |
| XI (2 Ig) | AXL, TYRO3 | none |
| XII | collagen (discoidin) receptors (2 known) | F11D5.3 (discussed here) |
| XIII | agrin receptor (MUSK) | none |
[i] The class definition is taken from Ullrich and Schlessinger (1990) and Rosnet and Birnbaum (1993) and updated. The order of classes is arbitrary.
[ii] When present in the extracellular region, the number of immunoglobulin-like domains (Ig) is indicated.