Ultrastructure and embryonic development of a syconoid calcareous sponge
Ultrastructure and embryonic development of a syconoid calcareous sponge
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DOI：
10.1111/j.1744-7410.2006.00051.x
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发表时间：
2006-01-01
影响因子：
1.2
通讯作者：
Leys, Sally P.
中科院分区：
文献类型：
--
作者：
Eerkes-Medrano, Dafne I.;Leys, Sally P.
最近的分子数据表明，孔类是并系（石灰+硅）和石灰是更密切相关的后生动物比其他海绵组，从而暗示海绵状动物引起了其他后生动物。这些数据的一个分支是，钙质海绵可以提供线索，说明这种祖先后生动物和高等动物之间共有哪些特征。最近的研究描述详细的形态在石灰岩是缺乏的。我们已经使用了显微镜技术相结合，研究Sycon coactum URBAN 1905，一个世界性的钙质海绵的精细结构。海绵有一个明显的极性，由一个顶端开放的小孔单管。手指状的腔室，几百微米长，形成管的侧面。室壁的内层和外层由上皮形成，其特征在于顶-底极性和细胞之间的封闭连接。外层--外胚层--和心房腔由板状细胞（外胚层细胞）排列，内层后鼻孔由连续的后鼻孔细胞排列。海绵的内流开口是由孔细胞形成的，孔细胞是连接口内胚层和后孔胚层的管状细胞。在这两层之间是一个胶原质的中胚叶，里面有硬细胞、骨针、变形虫细胞和胚胎阶段的进展。后鼻孔细胞和孔细胞的形态呈可塑性。孔关闭海绵，大力动摇和海绵留在静水中超过30分钟。Choanocytes，特别是衣领微绒毛，大小和形状不同，这取决于它们的位置在choanocyte室。虽然一些奇怪的形状的choanocytes和他们的衣领可以解释的发展大胚胎首先下面，后来在顶部的choanocytes，许多融合的衣领上的choanocytes微绒毛的存在可能反映了特殊性的流体动力学在大syconoid choanocytes室。不寻常的形成一个中空的囊胚幼虫和它的反转通过后鼻孔上皮细胞是上皮细胞，而不是间充质细胞运动的暗示。这些细节说明，钙质海绵具有与其他后生动物相比较的特征，这也是它们长期以来一直是进化和发展研究的焦点之一。
Recent molecular data suggest that the Porifera is paraphyletic (Calcarea+Silicea) and that the Calcarea is more closely related to the Metazoa than to other sponge groups, thereby implying that a sponge-like animal gave rise to other metazoans. One ramification of these data is that calcareous sponges could provide clues as to what features are shared among this ancestral metazoan and higher animals. Recent studies describing detailed morphology in the Calcarea are lacking. We have used a combination of microscopy techniques to study the fine structure of Sycon coactum URBAN 1905, a cosmopolitan calcareous sponge. The sponge has a distinct polarity, consisting of a single tube with an apically opening osculum. Finger-like chambers, several hundred micrometers in length, form the sides of the tube. The inner and outer layers of the chamber wall are formed by epithelia characterized by apical-basal polarity and occluding junctions between cells. The outer layer-the pinacoderm-and atrial cavity are lined by plate-like cells (pinacocytes), and the inner choanoderm is lined by a continuous sheet of choanocytes. Incurrent openings of the sponge are formed by porocytes, tubular cells that join the pinacoderm to the choanoderm. Between these two layers lies a collagenous mesohyl that houses sclerocytes, spicules, amoeboid cells, and a progression of embryonic stages. The morphology of choanocytes and porocytes is plastic. Ostia were closed in sponges that were vigorously shaken and in sponges left in still water for over 30 min. Choanocytes, and in particular collar microvilli, varied in size and shape, depending on their location in the choanocyte chamber. Although some of the odd shapes of choanocytes and their collars can be explained by the development of large embryos first beneath and later on top of the choanocytes, the presence of many fused collar microvilli on choanocytes may reflect peculiarities of the hydrodynamics in large syconoid choanocyte chambers. The unusual formation of a hollow blastula larva and its inversion through the choanocyte epithelium are suggestive of epithelial rather than mesenchymal cell movements. These details illustrate that calcareous sponges have characteristics that allow comparison with other metazoans-one of the reasons they have long been the focus of studies of evolution and development.