A sea urchin BMP2/4 homolog is expressed in presumptive ectoderm in the blastula embryo, and appears to influence ectoderm-endoderm boundary position by suppressing endoderm formation within presumptive ectoderm cells

نویسندگان

  • David R. Sherwood
  • David R. McClay
چکیده

In combination with classical manipulation studies, recent molecular analyses have begun to elucidate the cellular and molecular mechanisms that pattern the sea urchin animalvegetal (A-V) axis during early development (reviewed by Davidson et al., 1998; Logan and McClay, 1998; Wessel and Wikramanayake, 1999; Angerer and Angerer, 2000; Ettensohn and Sweet, 2000). This patterning process establishes three fundamental tissues along the A-V axis: mesoderm at the vegetal pole, endoderm overlying the mesoderm and ectoderm in the animal region of the embryo. A key event in this process is the placement of the boundary that divides the endoderm and ectoderm. This border separates the endoderm tissue that invaginates into the blastocoel during gastrulation from ectoderm tissue that remains outside to cover the embryo and larva. Embryological studies have suggested that cell-cell interactions play an important role in specifying the boundary between the ectoderm and endoderm. Lineage studies have revealed that the ectoderm-endoderm border does not correlate with early cleavage divisions, suggesting instead that cell-cell interactions establish this boundary (Logan and McClay, 1997; Ransick and Davidson, 1998). Supporting this notion, blastomere isolation experiments have shown that interactions between animal blastomeres suppress endoderm forming potential in presumptive ectoderm cells (Henry et al., 1989). In addition, blastomere removal and transplantation studies have indicated that the micromeres, the vegetal-most cells in the 16cell stage embryo, initiate a vegetal-to-animal wave of inductive signaling required for both normal overlying secondary mesenchyme cell (SMC) specification in the early blastula, and endoderm specification in the late blastula to early gastrula stage (Horstadius, 1973; Khaner and Wilt, 1991; Ransick and Davidson, 1993; Ransick and Davidson, 1995; Ransick and Davidson, 1998; Sweet et al., 1999; McClay et al., 2000). Recent work has begun to reveal the molecular mechanisms that regulate the position of the ectoderm-endoderm boundary. A sea urchin BMP2/4 homolog is expressed in presumptive ectoderm in the blastula embryo, and appears to influence ectoderm-endoderm boundary position by suppressing endoderm formation within presumptive ectoderm cells (Angerer et al., 2000). In addition, β-catenin, a component of the Wnt signaling pathway (reviewed in Wodarz and Nusse, 1998), may also have a role in mediating the position of the ectoderm-endoderm boundary. Nuclear β-catenin signaling is 2221 Development 128, 2221-2232 (2001) Printed in Great Britain © The Company of Biologists Limited 2001 DEV5908

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تاریخ انتشار 2001