Whitaker LL and Ramsdell AF (2005), Developmental analysis of activin-like kinase r...

XB-ART-2553

Dev Dyn 2005 Feb 01;2322:393-8. doi: 10.1002/dvdy.20232.

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Developmental analysis of activin-like kinase receptor-4 (ALK4) expression in Xenopus laevis.

Chen Y , Whitaker LL , Ramsdell AF .

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The type I transforming growth factor-beta (TGFbeta) receptor, activin-like kinase-4 (ALK4), is an important regulator of vertebrate development, with roles in mesoderm induction, primitive streak formation, gastrulation, dorsoanterior patterning, and left-right axis determination. To complement previous ALK4 functional studies, we have analyzed ALK4 expression in embryos of the frog, Xenopus laevis. Results obtained with reverse transcriptase-polymerase chain reaction indicate that ALK4 is present in both the animal and vegetal poles of blastula stage embryos and that expression levels are relatively constant amongst embryos examined at blastula, gastrula, neurula, and early tail bud stages. However, the tissue distribution of ALK4 mRNA, as assessed by whole-mount in situ hybridization, was found to change over this range of developmental stages. In the blastula stage embryo, ALK4 is detected in cells of the animal pole and the marginal zone. During gastrulation, ALK4 is detected in the outer ectoderm, involuting mesoderm, blastocoele roof, dorsal lip, and to a lesser extent, in the endoderm. At the onset of neurulation, ALK4 expression is prominent in the dorsoanterior region of the developing head, the paraxial mesoderm, and midline structures, including the prechordal plate and neural folds. Expression in older neurula stage embryos resolves to the developing brain, somites, notochord, and neural crest; thereafter, additional sites of ALK4 expression in tail bud stage embryos include the spinal cord, otic placode, developing eye, lateral plate mesoderm, branchial arches, and the bilateral heart fields. Together, these results not only reflect the multiple developmental roles that have been proposed for this TGFbeta receptor but also define spatiotemporal windows in which ALK4 may function to modulate fundamental embryological events.

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Species referenced: Xenopus laevis
Genes referenced: acvr1b tgfb1

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	Figure 2. ALK4 distribution in blastula stage embryos. A-H: Embryos were collected at stages 7 (A), 8 (C), and 9 (E,G) and whole-mount hybridized with either an ALK4 antisense probe (A,C,E) or ALK4 sense probe (G), followed by sectioning along the animal-vegetal axis (B,D,F,H). A higher magnification view of the outlined area in B is shown in the inset. ALK4, activin-like kinase-4; An, Animal; BC, blastocoele; MZ, marginal zone; Veg, vegetal.
	Figure 3. ALK4 distribution in gastrula stage embryos. A,C,E,G,J: Embryos were collected at stages 10 (A), 11 (C), 12 (E), and 13 (G) and whole-mount hybridized with either an ALK4 antisense probe (A,C,E,G) or ALK4 sense probe (J). B,D,F,H,I: Hybridized embryos were sectioned along the animal-vegetal axis (B,F), transversely (D,H), or sagittally (I,J). ALK4, activin-like kinase-4; ARC, archenteron; BC, blastocoele; BP, blastopore; DM, dorsal mesoderm; ECT, ectoderm; ENDO, endoderm; IDM, involuting dorsal marginal zone; IVM, involuting ventral marginal zone; NTC, notochord; PM, paraxial mesoderm; PCP, prechordal plate; VM, ventral mesoderm.
	Figure 4. ALK4 distribution in neurula stage embryos. A,C,E,G,J: Embryos were collected at stages 15 (A), 18 (C), 20 (E,G), 22 (I), and 24 (J) and whole-mount hybridized with either an ALK4 antisense probe (A,C,E,J) or ALK4 sense probe (G). B,D,F,H,I,K,L: Hybridized embryos were sectioned transversely (B,D,F,H,I) or sagittally (K,L). BA, branchial arches; CG, cement gland; ECT, ectoderm; EV, eye vesicle; HF, heart field; LPM, lateral plate mesoderm; NF, neural fold; NT, neural tube; NTC, notochord; OP, otic placode; SM, somitic mesoderm; SC, spinal cord.