Department of Molecular & Cell Biology, 385 LSA, University of California, Berkeley, Berkeley, CA 94720-3200, USA.
Curr Biol. 2011 Aug 9;21(15):1282-8. doi: 10.1016/j.cub.2011.06.024. Epub 2011 Jul 21.
Bone morphogenetic protein (BMP) signaling is broadly implicated in dorsoventral (DV) patterning of bilaterally symmetric animals [1-3], and its role in axial patterning apparently predates the birth of Bilateria [4-7]. In fly and vertebrate embryos, BMPs and their antagonists (primarily Sog/chordin) diffuse and interact to generate signaling gradients that pattern fields of cells [8-10]. Work in other species reveals diversity in essential facets of this ancient patterning process, however. Here, we report that BMP signaling patterns the DV axis of segmental ectoderm in the leech Helobdella, a clitellate annelid (superphylum Lophotrochozoa) featuring stereotyped developmental cell lineages, but the detailed mechanisms of DV patterning in Helobdella differ markedly from fly and vertebrates. In Helobdella, BMP2/4s are expressed broadly, rather than in dorsal territory, whereas a dorsally expressed BMP5-8 specifies dorsal fate by short-range signaling. A BMP antagonist, gremlin, is upregulated by BMP5-8 in dorsolateral, rather than ventral territory, and yet the BMP-antagonizing activity of gremlin is required for normal ventral cell fates. Gremlin promotes ventral fates without disrupting dorsal fates by selectively inhibiting BMP2/4s, not BMP5-8. Thus, DV patterning in the development of the leech revealed unexpected evolutionary plasticity of the conserved BMP patterning system, presumably reflecting its adaptation to different modes of embryogenesis.
骨形态发生蛋白 (BMP) 信号广泛参与双侧对称动物的背腹 (DV) 模式形成 [1-3]，其在轴向模式形成中的作用显然先于双细胞动物的出现 [4-7]。在果蝇和脊椎动物胚胎中，BMP 及其拮抗剂（主要是 Sog/chordin）扩散并相互作用，以产生模式化细胞场的信号梯度 [8-10]。然而，在其他物种中的工作揭示了这个古老的模式形成过程的基本方面的多样性。在这里，我们报告 BMP 信号在环节动物蛭形蚓（具节环节动物门，Lophotrochozoa 超级门）的节段外胚层中模式化 DV 轴，其具有定型的发育细胞谱系，但 Helobdella 中的 DV 模式形成的详细机制与果蝇和脊椎动物明显不同。在 Helobdella 中，BMP2/4s 广泛表达，而不是在背侧区域，而表达于背侧的 BMP5-8 通过短程信号来指定背侧命运。BMP 拮抗剂 gremlin 在背侧和侧部而非腹侧区域上调，然而，gremlin 的 BMP 拮抗活性对于正常的腹侧细胞命运是必需的。Gremlin 通过选择性抑制 BMP2/4s 而不是 BMP5-8 促进腹侧命运，而不会破坏背侧命运。因此，在蛭形蚓的发育中，DV 模式形成揭示了保守的 BMP 模式形成系统的出人意料的进化可塑性，可能反映了其对不同胚胎发生模式的适应。
