Evolution of a New Function by Degenerative Mutation in Cephalochordate Steroid Receptors
Alternating cross-sections of adult animals were probed with digoxigenin-labelled RNAs for Bfer, Bfsr, or Vasa, a germ cell marker. A–F) In adult females, expression of Bfer and Bfsr are co-localized in the cytoplasm of oocytes in the ovary (o); er is also weakly expressed in the female gill bars (g). The negative control experiment with no probe (inset in A) shows no endogenous alkaline phosphatase activity. G–L) In adult males Bfer and Vasa are expressed only in a single cell layer of early spermatogonia in the testicular epithelium, but Bfsr is expressed throughout testes (t). Myotome (m) and notochord (n) are also labeled. Scale bars are indicated.