Departament de Genètica and Institut de Biomedicina (IBUB), University of Barcelona, Av. Diagonal, 643, 08028 Barcelona, Spain.
Dev Biol. 2013 Mar 15;375(2):182-92. doi: 10.1016/j.ydbio.2012.11.015. Epub 2012 Nov 27.
The vertebrate circulatory system is the most complex vascular system among those of metazoans, with key innovations including a multi-chambered heart and highly specialized blood cells. Invertebrate vessels, on the other hand, consist of hemal spaces between the basal laminae of epithelia. How the evolutionary transition from an invertebrate-type system to the complex vertebrate one occurred is, however, poorly understood. We investigate here the development of the cardiovascular system of the cephalochordate amphioxus Branchiostoma lanceolatum in order to gain insight into the origin of the vertebrate cardiovascular system. The cardiac markers Hand, Csx (Nkx2-5) and Tbx4/5 reveal a broad cardiac-like domain in amphioxus; such a decentralized organization during development parallels that seen in the adult anatomy. Our data therefore support the hypothesis that amphioxus never possessed a proper heart, even transiently during development. We also define a putative hematopoietic domain, supported by the expression of the hematopoietic markers Scl and Pdvegfr. We show that this area is closed to the dorsal aorta anlages, partially linked to excretory tissues, and that its development is regulated by retinoic acid, thus recalling the aorta-gonads-mesonephros (AGM) area of vertebrates. This region probably produces Pdvegfr+ hemal cells, with an important role in amphioxus vessel formation, since treatments with an inhibitor of PDGFR/VEGFR lead to a decrease of Laminin in the basal laminae of developing vessels. Our results point to a chordate origin of hematopoiesis in an AGM-like area from where hemal Pdvegfr+ cells are produced. These Pdvegfr+ cells probably resemble the ancestral chordate blood cells from which the vertebrate endothelium later originated.
脊椎动物的循环系统是后生动物中最复杂的血管系统，其关键创新包括具有多个腔室的心脏和高度特化的血细胞。相比之下，无脊椎动物的血管由上皮基底膜之间的血腔组成。然而，从无脊椎动物类型的系统向复杂的脊椎动物系统的进化过渡是如何发生的，还知之甚少。我们在这里研究了文昌鱼（Branchiostoma lanceolatum）的心血管系统的发育，以便深入了解脊椎动物心血管系统的起源。心脏标志物 Hand、Csx（Nkx2-5）和 Tbx4/5 在文昌鱼中揭示了一个广泛的心脏样区域；这种在发育过程中的分散组织与成年解剖结构中的组织相似。因此，我们的数据支持文昌鱼从未拥有过真正的心脏的假设，即使在发育过程中短暂存在。我们还定义了一个假定的造血区域，该区域由造血标志物 Scl 和 Pdvegfr 的表达支持。我们表明，该区域与背主动脉原基接近，部分与排泄组织相关，其发育受到视黄酸的调节，因此回忆起脊椎动物的主动脉-性腺-中肾（AGM）区域。这个区域可能产生 Pdvegfr+ 血腔细胞，在文昌鱼血管形成中起着重要作用，因为用 PDGFR/VEGFR 的抑制剂处理会导致发育中的血管基底膜中的层粘连蛋白减少。我们的结果表明，造血是在 AGM 样区域从那里产生血腔 Pdvegfr+ 细胞的脊索动物起源。这些 Pdvegfr+ 细胞可能类似于祖先脊索动物血细胞，后来脊椎动物的内皮细胞就是从这些血细胞起源的。
