Fig. 4

The ALK2 receptor positively regulates the expression of organizer genes. The truncated, dominant negative form of ALK2 (tALK2) was employed to corroborate the function of this receptor in the expansion of the organizer. Embryos were injected with mRNA (1.3 ng/embryo) encoding tALK2 or the truncated ALK3 (tALK3) in order to block their activity. At the onset of gastrulation, the effect of blocking these receptors on the expression domains of chordin (a–d), gsc (e–h), and ADMP (i–l) was determined by in situ hybridization with specific probes. The relative size of the expression domain (%) was determined. Chordin analysis: control, n = 28; tALK2, n = 20; tALK3, n = 15, gsc analysis: control, n = 20; tALK2, n = 26; tALK3, n = 23, and ADMP analysis: control, n = 10; tALK2, n = 18; tALK3, n = 19. p values were calculated compared to controls. Statistical test; Dunnett’s (ANOVA) multiple comparisons test. **p < 0.01, ***p < 0.001, ****p < 0.0001