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The ancient origin of the complement system.

ABSTRACT: The complement system has been thought to originate exclusively in the deuterostomes. Here, we show that the central complement components already existed in the primitive protostome lineage. A functional homolog of vertebrate complement 3, CrC3, has been isolated from a 'living fossil', the horseshoe crab (Carcinoscorpius rotundicauda). CrC3 resembles human C3 and shows closest homology to C3 sequences of lower deuterostomes. CrC3 and plasma lectins bind a wide range of microbes, forming the frontline innate immune defense system. Additionally, we identified CrC2/Bf, a homolog of vertebrate C2 and Bf that participates in C3 activation, and a C3 receptor-like sequence. Furthermore, complement-mediated phagocytosis of bacteria by the hemocytes of horseshoe crab was also observed. Thus, a primitive yet complex opsonic complement defense system is revealed in the horseshoe crab, a protostome species. Our findings demonstrate an ancient origin of the critical complement components and the opsonic defense mechanism in the Precambrian ancestor of bilateral animals.

SUBMITTER: Zhu Y

PROVIDER: S-EPMC545819 | biostudies-literature | 2005 Jan

REPOSITORIES: biostudies-literature

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The ancient origin of the complement system.

Zhu Yong Y Thangamani Saravanan S Ho Bow B Ding Jeak Ling JL

The EMBO journal 20041223 2

The complement system has been thought to originate exclusively in the deuterostomes. Here, we show that the central complement components already existed in the primitive protostome lineage. A functional homolog of vertebrate complement 3, CrC3, has been isolated from a 'living fossil', the horseshoe crab (Carcinoscorpius rotundicauda). CrC3 resembles human C3 and shows closest homology to C3 sequences of lower deuterostomes. CrC3 and plasma lectins bind a wide range of microbes, forming the fr ...[more]

PMID: 15616573

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Project description:BACKGROUND: A key to understanding the evolution of the nervous system on a large phylogenetic scale is the identification of homologous neuronal types. Here, we focus this search on the sensory and motor neurons of bilaterians, exploiting their well-defined molecular signatures in vertebrates. Sensorimotor circuits in vertebrates are of two types: somatic (that sense the environment and respond by shaping bodily motions) and visceral (that sense the interior milieu and respond by regulating vital functions). These circuits differ by a small set of largely dedicated transcriptional determinants: Brn3 is expressed in many somatic sensory neurons, first and second order (among which mechanoreceptors are uniquely marked by the Brn3+/Islet1+/Drgx+ signature), somatic motoneurons uniquely co-express Lhx3/4 and Mnx1, while the vast majority of neurons, sensory and motor, involved in respiration, blood circulation or digestion are molecularly defined by their expression and dependence on the pan-visceral determinant Phox2b. RESULTS: We explore the status of the sensorimotor transcriptional code of vertebrates in mollusks, a lophotrochozoa clade that provides a rich repertoire of physiologically identified neurons. In the gastropods Lymnaea stagnalis and Aplysia californica, we show that homologues of Brn3, Drgx, Islet1, Mnx1, Lhx3/4 and Phox2b differentially mark neurons with mechanoreceptive, locomotory and cardiorespiratory functions. Moreover, in the cephalopod Sepia officinalis, we show that Phox2 marks the stellate ganglion (in line with the respiratory--that is, visceral--ancestral role of the mantle, its target organ), while the anterior pedal ganglion, which controls the prehensile and locomotory arms, expresses Mnx. CONCLUSIONS: Despite considerable divergence in overall neural architecture, a molecular underpinning for the functional allocation of neurons to interactions with the environment or to homeostasis was inherited from the urbilaterian ancestor by contemporary protostomes and deuterostomes.

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The ancient origin of the complement system.

Publications

The ancient origin of the complement system.

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