Depending upon the nature of their interaction with SHH, they are classified into two groups, class I and class II, and are composed of members from the Pax, Nkx, Dbx, and Irx families.
Dependendo da natureza da súa interacción con SHH, clasifícanse en dous grupos, clase I e clase II, e están compostos de membros das familias Pax, Nkx, Dbx e Irx.