Hemmati-Brivanlou A, Thomsen G H
Rockefeller University, New York City, NY, USA.
Dev Genet. 1995;17(1):78-89. doi: 10.1002/dvg.1020170109.
We provide a comparative analysis of the expression patterns and ventral mesoderm-inducing properties of Xenopus BMP-2 and BMP-4. Transcripts for BMP-2 and BMP-4 are maternally stored in eggs, and zygotic expression of these genes is uniform in the ectoderm and mesoderm in late blastulae. During gastrulation, BMP-2 is expressed at a low level throughout the ectoderm and marginal zone, but at early neurula stages a patch of dorso-anterior cells displays enhanced expression. In contrast, BMP-4 transcripts are restricted to the ventrolateral marginal zone during gastrulation, and in late gastrula and early neurula BMP-4 is expressed in the epidermis but not the neural plate. At post-neurula stages, BMP-2 and BMP-4 transcripts are associated with a variety of mesodermal structures, including the pharyngeal pouches, heart, blood island, and blastopore. At tailbud stages, BMP-2 and BMP-4 are expressed in neural tissues including the neural tube and brain. In mesoderm induction assays, BMP-2 and BMP-4 induce Xhox3, an early ventral-posterior mesoderm marker, and larval alpha Tl globin, a marker for red blood cells. Induction of red blood cells in response to BMP-4 was demonstrated by staining with a hemoglobin-specific reagent. Little is known about factors that induce hematopoietic lineages in vertebrates, and these results provide evidence linking BMP activity and blood differentiation. Globin induction by BMP-2 and BMP-4 is blocked by co-expression of a dominant-negative activin receptor, suggesting that either endogenous activin signals are required for BMP-mediated induction, or that the truncated activin receptor interferes with signaling by BMP receptors. In assays on marginal zone explants, we demonstrate that BMP-4 respecifies dorsal mesoderm to form ventral mesoderm, consistent with its ability to induce blood and to ventralize embryos. BMP-2, however, does not display such activity. The findings extend and support evidence that BMP-2 and BMP-4 function in ventral mesoderm induction and patterning in Xenopus. Our data furthermore highlight the multiple functions these factors fulfill during early vertebrate embryogenesis.
我们对非洲爪蟾BMP - 2和BMP - 4的表达模式及诱导腹侧中胚层的特性进行了比较分析。BMP - 2和BMP - 4的转录本在卵中母源储存，这些基因在囊胚后期的外胚层和中胚层中合子表达是均匀的。在原肠胚形成期间，BMP - 2在整个外胚层和边缘区低水平表达，但在神经胚早期，一群背前部细胞显示出增强的表达。相比之下，BMP - 4转录本在原肠胚形成期间局限于腹外侧边缘区，在原肠胚后期和神经胚早期，BMP - 4在表皮而非神经板中表达。在神经胚后期阶段，BMP - 2和BMP - 4转录本与多种中胚层结构相关，包括咽囊、心脏、血岛和胚孔。在尾芽期，BMP - 2和BMP - 4在包括神经管和脑在内的神经组织中表达。在中胚层诱导试验中，BMP - 2和BMP - 4诱导早期腹侧 - 后中胚层标记物Xhox3以及红细胞标记物幼虫α Tl球蛋白。用血红蛋白特异性试剂染色证明了BMP - 4诱导红细胞的产生。关于诱导脊椎动物造血谱系的因子知之甚少，这些结果提供了将BMP活性与血液分化联系起来的证据。BMP - 2和BMP - 4诱导球蛋白的过程被显性负性激活素受体的共表达所阻断，这表明要么内源性激活素信号是BMP介导的诱导所必需的，要么是截短的激活素受体干扰了BMP受体的信号传导。在边缘区外植体试验中，我们证明BMP - 4使背侧中胚层重新指定形成腹侧中胚层，这与其诱导血液和使胚胎腹侧化的能力一致。然而，BMP - 2不显示这种活性。这些发现扩展并支持了BMP - 2和BMP - 4在非洲爪蟾腹侧中胚层诱导和模式形成中起作用的证据。我们的数据进一步突出了这些因子在早期脊椎动物胚胎发生过程中所发挥的多种功能。
