Pancer Z, Kruse M, Schäcke H, Scheffer U, Steffen R, Kovács P, Müller W E
Institut für Physiologische Chemie, Universität, Mainz, Germany.
Cell Adhes Commun. 1996 Nov;4(4-5):327-39. doi: 10.3109/15419069609010776.
Sponges [Porifera] are the phylogenetically oldest phylum of the Metazoa. They are provided with both cellular and humoral allorecognition systems. The underlying molecules are not yet known. To study allorecognition in sponges we first determined the frequency of graft rejection in a natural population of the marine sponge Geodia cydonium. We then determined, for the first time at the molecular level, the degree of sequence polymorphism in segments of one molecule which may be related to sponge allorecognition and host defense: the Ig-like domains from the receptor tyrosine kinase [RTK]. Thirty six pairs of auto- and allografts were assayed, either by parabiotic attachment or insertion of grafts. All of the autografts fused, while only two allografts fused and 34 pairs were incompatible. Rejection among the parabiotic allografts was characterized by the formation of a collagenous barrier, while the allografts that were inserted into the host underwent destruction. At the molecular level we first cloned to completion the 5'-end of sponge RTK, which displays a Pro-Ser-Thr-rich sequence; this is thought to act as a module of cell adhesion proteins. Then we analyzed RT-PCR products of amplification across the two Ig-like domains of RTK (about 500 bp), from two pairs of fusing sponges and one pair of rejecting sponges. High levels of polymorphism were recorded, including 18 nucleotide-substitution positions and a tri-nucleotide deletion, which translate into 13 polymorphic amino acid positions. Two of the six sponges were scored as heterozygotes. Among 9 informative polymorphic sites that were tested for linkage disequilibrium, 11 pairwise comparisons were found to be significant, implying the possibility of distinguishable alleles in this locus. To the best of our knowledge this is the first report of polymorphism in Ig-like domains of a receptor from invertebrates that may be associated with allorecognition. This data attests also that fusion in sponges is not confined to genetically identical individuals.
海绵动物门是后生动物中系统发育最古老的门类。它们拥有细胞和体液同种异体识别系统。其潜在分子尚不清楚。为了研究海绵动物的同种异体识别，我们首先确定了海洋海绵地穴海绵自然种群中移植排斥的频率。然后，我们首次在分子水平上确定了一种可能与海绵同种异体识别和宿主防御相关的分子片段中的序列多态性程度：来自受体酪氨酸激酶（RTK）的免疫球蛋白样结构域。通过联体附着或移植插入的方式检测了36对自体移植和异体移植。所有自体移植都融合了，而异体移植中只有2对融合，34对不相容。联体异体移植中的排斥反应表现为形成胶原屏障，而插入宿主体内的异体移植则会被破坏。在分子水平上，我们首先完全克隆了海绵RTK的5'端，其显示出富含脯氨酸-丝氨酸-苏氨酸的序列；这被认为是细胞粘附蛋白的一个模块。然后，我们分析了来自两对融合海绵和一对排斥海绵的RTK两个免疫球蛋白样结构域（约500 bp）的扩增RT-PCR产物。记录到高水平的多态性，包括18个核苷酸取代位置和一个三核苷酸缺失，这转化为13个多态性氨基酸位置。6个海绵中有2个被判定为杂合子。在9个用于连锁不平衡测试的信息性多态位点中，发现11对两两比较具有显著性，这意味着该位点可能存在可区分的等位基因。据我们所知这是首次报道可能与同种异体识别相关的无脊椎动物受体免疫球蛋白样结构域中的多态性。这些数据也证明了海绵动物中的融合并不局限于基因相同的个体。
