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β-Catenin is essential for patterning the maternally specified animal-vegetal axis in the sea urchin embryo

  1. William H. Klein*
  1. Department of Biochemistry and Molecular Biology, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030

  1. Communicated by William J. Lennarz, State University of New York, Stony Brook, NY

  1. Figure 1
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    Figure 1

    Vegetalization of embryos by β-catenin and lithium. (A) A vegetalized embryo developing from an egg injected with pt β-catenin (amino terminal serine/threonine mutated to alanine) RNA. The arrow points to the remaining ectoderm in this embryo. The increased number of secondary mesoderm-derived pigment cells are seen clearly in this embryo. (B) A vegetalized embryo resulting from incubation in 35 mM lithium chloride. The arrow points to the remaining ectoderm in this embryo. (C) A pluteus larva developing from an egg injected with an RNA encoding a truncated β-catenin (HT-6) protein (lacking the armadillo repeats 5–13).

  2. Figure 2
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    Figure 2

    Induction of endoderm in animal halves by β-catenin. (A) Protocol for introducing mRNA into animal halves. (B) An animal half made from an embryo that was injected at the one-cell stage with an RNA encoding a truncated β-catenin protein (HT-6). It develops as a polarized embryoid that does not form aboral ectoderm, endoderm, or mesoderm. (C) Induction of endoderm and gastrulation in an animal half made from an embryo injected at the one-cell stage with pt β-catenin RNA.

  3. Figure 3
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    Figure 3

    Patterning of ectoderm by low concentrations of β-catenin. (A) Induction of aboral ectoderm in isolated animal halves by β-catenin. RT-PCR was used to monitor the expression of aboral ectoderm and endoderm-specific markers. LvS1 is an aboral ectoderm-specific marker; LvEndo16 and LvN1.2 are endoderm-specific markers. Actin primers were used to monitor input cDNA for each sample. The autoradiograph shows that aboral ectoderm is induced after injection of a low concentration of pt β-catenin RNA into animal halves whereas expression of endodermal markers is not detected. (B) Animal half made from an HT-6 RNA-injected embryo. (C and D) Patterning of ectoderm by low concentrations of pt β-catenin. (C) Induction of a stomodeum in a pt β-catenin-injected animal half (arrow). (D) Induction of a ciliary band in a pt β-catenin-injected animal half (arrows).

  4. Figure 4
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    Figure 4

    Animalization of sea urchin embryos by overexpression of C-cadherin. (A and B) Morphology of control and C-cadherin RNA-injected embryos. (A) Uninjected embryo at the early prism stage. (B) An embryo animalized by C-cadherin. It is radialized and does not develop endoderm or mesoderm, and long cilia are seen in the cuboidal epithelium. (C) RT-PCR analysis of C-cadherin RNA-injected embryos. In addition to the loss of the endodermal markers LvEndo16 and LvN1.2, these embryos do not express the aboral ectoderm-specific marker LvS1. (D, E, F, and G) Expression of the oral ectoderm marker Ecto V in control embryos (D and E) and C-cadherin RNA-injected embryos (F and G). (D and F) Differential interference contrast images. (E and G) Corresponding indirect immunofluorescent images. In control embryos, the Ecto V antigen is localized to the oral ectoderm whereas, in the C-cadherin RNA-injected embryos, the Ecto V antigen is seen on the surface of all blastomeres. (H) RT-PCR analysis of C-cadherin RNA and pt β-catenin RNA co-injected embryos. Autoradiograph shows that, although marker genes for endoderm and aboral ectoderm are not expressed in C-cadherin-injected embryos, they are rescued with injection of pt β-catenin RNA.

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