University of Chicago, Department of Organismal Biology and Anatomy, Chicago, IL 60637, USA.
Development. 2012 Sep;139(18):3373-82. doi: 10.1242/dev.083873. Epub 2012 Aug 8.
Bone morphogenetic protein (BMP) signaling is an essential factor in dorsoventral patterning of animal embryos but how BMP signaling evolved with fundamental changes in dorsoventral tissue differentiation is unclear. Flies experienced an evolutionary reduction of extra-embryonic tissue types from two (amniotic and serosal tissue) to one (amnionserosal tissue). BMP-dependent amnioserosa specification has been studied in Drosophila melanogaster. However, the mechanisms of serosal and amniotic tissue specification in less diverged flies remain unknown. To better understand potential evolutionary links between BMP signaling and extra-embryonic tissue specification, we examined the activity profile and function of BMP signaling in serosa and amnion patterning of the scuttle fly Megaselia abdita (Phoridae) and compared the BMP activity profiles between M. abdita and D. melanogaster. In blastoderm embryos of both species, BMP activity peaked at the dorsal midline. However, at the beginning of gastrulation, peak BMP activity in M. abdita shifted towards prospective amnion tissue. This transition correlated with the first signs of amnion differentiation laterally adjacent to the serosa anlage. Marker-assisted analysis of six BMP signaling components (dpp, gbb, scw, tkv, sax, sog) by RNA interference revealed that both serosa and amnion specification of M. abdita are dependent on BMP activity. Conversely, BMP gain-of-function experiments caused sharpened expression boundaries of extra-embryonic target genes indicative of positive feedback. We propose that changes in the BMP activity profile at the beginning of gastrulation might have contributed to the reduction of extra-embryonic tissue types during the radiation of cyclorrhaphan flies.
骨形态发生蛋白（BMP）信号是动物胚胎背腹模式形成的一个重要因素，但 BMP 信号如何随着背腹组织分化的基本变化而进化尚不清楚。苍蝇经历了从两种（羊膜和浆膜组织）到一种（羊膜浆膜组织）的胚胎外组织类型的进化减少。在黑腹果蝇中已经研究了 BMP 依赖性的浆膜特化。然而，在分化程度较低的苍蝇中浆膜和羊膜组织特化的机制仍然未知。为了更好地理解 BMP 信号与胚胎外组织特化之间的潜在进化联系，我们研究了鞘翅目昆虫（Megaselia abdita）的浆膜和羊膜模式形成中 BMP 信号的活性谱和功能，并比较了 M. abdita 和 D. melanogaster 之间的 BMP 活性谱。在这两个物种的胚盘胚胎中，BMP 活性在背中线达到峰值。然而，在原肠胚形成开始时，M. abdita 中的峰值 BMP 活性向预期的羊膜组织转移。这种转变与浆膜原基旁边侧向出现的羊膜分化的最初迹象相关。通过 RNA 干扰对六个 BMP 信号成分（dpp、gbb、scw、tkv、sax、sog）的标记辅助分析表明，M. abdita 的浆膜和羊膜特化都依赖于 BMP 活性。相反，BMP 功能获得实验导致胚胎外靶基因的表达边界变得更加锐利，表明存在正反馈。我们提出，原肠胚形成开始时 BMP 活性谱的变化可能有助于在环裂蝇辐射过程中减少胚胎外组织类型。
