Haag E S, Raff R A
Department of Biology and Indiana Molecular Biology Institute, Indiana University, Bloomington, IN 47405, USA.
Dev Genes Evol. 1998 Jun;208(4):188-204. doi: 10.1007/s004270050173.
The Australian sea urchin Heliocidaris erythro-gramma utilizes a derived direct developmental mode that evolved 8-12 million years ago. From a differential screen we have isolated a small set of cDNAs corresponding to genes more greatly expressed in embryos of H. erythrogramma than in those of its indirect-developing nearest relative, H. tuberculata. The method was biased towards abundant transcripts and did not allow detection of modifications of usage of highly conserved gene family members. Three differentially expressed abundant transcripts were found that potentially encode secreted proteins. Two of these, the arylsulfatase HeARS and the putative lectin HeEL-1, were identifiable as homologues of known proteins. Another gene, HeET-1, may be exclusively expressed in the H. erythrogramma embryo. In situ hybridization experiments demonstrate that all three transcripts are localized to the ectoderm. Two of them, HeET-1 and HeEL-1, are transcribed in an identical domain comprising the larval ectoderm. This region of gene expression has acquired a novel columnar cytology during the evolution of the H. erythrogramma embryo. The third sequence, HeARS, encodes an arylsulfatase homologue. Its expression is uniform in the gastrula, but as the rudiment develops it accumulates to the greatest extent in the invaginating vestibular ectoderm. Through comparisons with indirect-developing species, we show that this concentration of arylsulfatase mRNA in the rudiment is a novel feature of H. erythrogramma development. These data suggest that H. erythrogramma has a unique arrangement of ectodermal gene expression territories. We propose that these reflect larval adaptations that have occurred in the lineage leading to H. erythrogramma, and enabled the evolution of direct development.
澳大利亚海胆红斑疣海胆采用一种在800万至1200万年前进化而来的衍生直接发育模式。通过差异筛选，我们分离出了一小部分cDNA，它们对应的基因在红斑疣海胆胚胎中的表达量比其间接发育的近缘种——瘤海胆胚胎中的表达量更高。该方法偏向于高丰度转录本，无法检测到高度保守基因家族成员使用情况的变化。我们发现了三种差异表达的高丰度转录本，它们可能编码分泌蛋白。其中两种，芳基硫酸酯酶HeARS和假定的凝集素HeEL - 1，可以鉴定为已知蛋白质的同源物。另一个基因HeET - 1可能仅在红斑疣海胆胚胎中表达。原位杂交实验表明，这三种转录本都定位于外胚层。其中两种，HeET - 1和HeEL - 1，在包括幼虫外胚层的同一区域转录。在红斑疣海胆胚胎的进化过程中，这个基因表达区域获得了一种新的柱状细胞学特征。第三个序列HeARS编码一种芳基硫酸酯酶同源物。它在原肠胚中的表达是均匀的，但随着原基的发育，它在向内凹陷的前庭外胚层中积累到最大程度。通过与间接发育物种的比较，我们表明原基中芳基硫酸酯酶mRNA的这种集中是红斑疣海胆发育的一个新特征。这些数据表明，红斑疣海胆具有外胚层基因表达区域的独特排列。我们认为，这些反映了在导致红斑疣海胆的谱系中发生的幼虫适应性变化，并促成了直接发育的进化。
