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Fig. 5. Localized expression of xSP-C and xSP-B in the developing lung. In situ hybridization performed on Xenopus embryos provides evidence that the expression of surfactant protein genes is localized to the lung. Whole mount in situ hybridization was performed using antisense RNA probes for xSP-C (A–C and E–F), Nkx2.1 (D), and xSP-B (G–I). (A) xSP-C is expressed in a broad crescent shape as viewed dorsally in a stage 41 embryo. (B) xSP-C expression expands in the growing tubules of the lung at stage 44. (C) Lateral view of a stage 43 embryo shows xSP-C expression just dorsal to the coiling gut tube. (E) Transverse section of a stage 41 embryo shows xSP-C expression in the two lung tubes (arrows). (F) More anterior transverse section of the same embryo in (E) shows xSP-C expression in a single tube (arrow) before lung has split into two tubules. (H) SP-B is also expressed in a broad crescent shape as viewed dorsally in a stage 41 embryo. (I) xSP-B expression expands in the growing tubules of the lung at stage 44. (G) Transverse section of a stage 39 embryo shows expression of xSP-B in a widening tube (arrow) just anterior to the splitting of the two lung tubules. (D) Nkx2.1 is expressed in the forebrain (little arrow), thyroid (arrowhead), and lung (big arrow) at stage 36, preceding expression of xSP-C and xSP-B in the lung. Scale bar in (A) represents 0.5 mm in all panels. |
