棘皮動物同源區基因的選殖和 Xlox族同源區基因在海星胚胎時期表現的研究

Abstract

本論文以聚合?連鎖反應增殖馬糞海膽和飛白楓海星的同源區基因片段以及以反轉錄聚合?連鎖反應研究飛白楓海星胚胎時期表現Xlox 族同源區基因的 mRNA 的情形。聚合?連鎖反應產物經選殖計得八段，與已知同源區基因序列進行比對後，顯示其中六段是Hox 型的同源區基因片段。這六段中，一段可能屬於前端型群，三段可能屬於中間型群，二段可能屬於後端型群，因此棘皮動物可能只有一組的同源異性基因組。不同於親緣關係相近的半索動物和頭索動物，棘皮動物只有一個前端型群的基因，這可能與棘皮動物沒有頭化的現象有關。棘皮動物至少有兩個屬於後端型群的基因，顯示和其他後口類一樣，有後端型群基因的複製情形。另外兩段選殖片段是馬糞海贍和飛白楓海星的Xlox 族同源區基因片段。從反轉錄聚合?連鎖反應的結果，發現在飛白楓海星胚胎在兩個時期表現Xlox 族同源區基因的 mRNA ：即未受精卵到卵割期，以及原腸期到早期雙羽腕幼生。因此 Xlox 族同源區基因前期的表現，可能扮演著母體效應基因的角色；後期的表現可能參與棘皮動物腸體腔的形成，或腸道細胞的分化。

The polymerase chain reaction was carried out in order to survey the homeobox-gene fragments of sea urchin, Tripneustes gratilla, and starfish Archaster typicus. A total eight sequences were identified. The results of comparative analysis with known homeobox sequences suggested that six sequences were of the Hox type. One of the six sequences may be the anterior-type group gene, four may be the medial-type ones, and two may be the posterior-type ones. These results suggested that echinoderms may have a single cluster of Hox-Complex. Possibly, only one anterior-type group gene exists in echinoderms, which is different from the hemichordates and the cephalochordates that are close relatives of echinoderms. This difference is probably due to the lack of cephalic structures in the echinodermae body form. Echinoderms have at least two posterior-type homeobox genes, implying that the tandem duplication of the ancestral gene of this group occurred in echinoderms as other deuterostomes. Besides, two sequences were of the Xlox family of the sea urchin and the starfish. In addition, the expression of the Xlox family homeobox gene in the starfish embryos was detected by reverse transcription polyrnerase chain reactions. The expression of mRNA of the Xlox family gene in the starfish embryos was detected during two periods from egg to cleavage and from gastrula to early bipinnaria. A maternal effect role in the early development and a role in the enteroceol formation or the differentiation of the gut cells in the later period are proposed for the Xlox family gene.