Hoffmann U, Kroiher M
Zoologisches Institut, Universität zu Köln, Weyertal 119, Köln, 50923, Germany.
Dev Biol. 2001 Aug 15;236(2):304-15. doi: 10.1006/dbio.2001.0335.
We have isolated the serum response factor (SRF) homologue from two hydrozoans, the freshwater polyp Hydra vulgaris and the marine colonial Hydractinia echinata; we have termed the Hydra gene HvSRF and the Hydractinia gene HeSRF. The MADS-box of both genes is identical in sequence and more similar to SRFs of other organisms than to non-SRF MADS-box-containing proteins from other organisms. Within the N terminus of the predicted protein, a motif of 14 amino acids is nearly identical between Hydra and Hydractinia. This motif is absent from other known SRF sequences. In the adult Hydra polyp, SRF is predominantly expressed in cells of the interstitial cell (I-cell) lineage. Expression of SRF ceases when I-cells differentiate into nerve cells, nematocytes, or gland cells. In the course of sexual reproduction in Hydractinia, SRF is expressed in female germ cells. During embryogenesis, SRF transcripts are observed in all blastomeres. Later on, SRF expression is turned off in cells forming the ectodermal layer but further on is expressed in cells of the central cell mass, from which the endodermal epithelial cells and the I-cell lineage originate. Expression eventually becomes restricted to the I-cell lineage. We conclude that hydrozoan SRF is expressed in all these cells, which still have the property for differentiation. In adult Hydra, the abundance of SRF transcripts varies during the day. The pacemaker of this diurnal rhythm is the feeding regime. HvSRF expression decreases by 4 h after feeding and returns to the initial level 12 h after feeding. When feeding is stopped, the cycle of SRF expression persists through the first day when the animals are not fed. It has been shown that feeding partly synchronizes the cell cycle of the epithelial cells but not that of the I-cells. We suggest that the epithelial cells affect SRF expression in I-cells and thereby influence the decision of I-cells to enter a differentiation pathway.
我们从两种水螅虫中分离出了血清反应因子（SRF）同源物，即淡水水螅Hydra vulgaris和海洋群体水螅Hydractinia echinata；我们将水螅的基因命名为HvSRF，将Hydractinia的基因命名为HeSRF。这两个基因的MADS盒在序列上是相同的，并且与其他生物的SRF比与来自其他生物的不含SRF的MADS盒蛋白更为相似。在预测蛋白的N端，水螅和Hydractinia之间有一个14个氨基酸的基序几乎相同。其他已知的SRF序列中没有这个基序。在成年水螅虫中，SRF主要在间充质细胞（I细胞）谱系的细胞中表达。当I细胞分化为神经细胞、刺细胞或腺细胞时，SRF的表达停止。在Hydractinia有性生殖过程中，SRF在雌性生殖细胞中表达。在胚胎发育过程中，在所有卵裂球中都观察到SRF转录本。后来，SRF表达在形成外胚层的细胞中关闭，但在中央细胞团的细胞中继续表达，内胚层上皮细胞和I细胞谱系由此起源。表达最终局限于I细胞谱系。我们得出结论，水螅虫的SRF在所有这些仍具有分化特性的细胞中表达。在成年水螅中，SRF转录本的丰度在一天中有所变化。这种昼夜节律的起搏器是摄食模式。喂食后4小时，HvSRF表达下降，喂食后12小时恢复到初始水平。当停止喂食时，SRF表达周期在动物未进食的第一天持续存在。已经表明，喂食部分同步上皮细胞的细胞周期，但不影响I细胞的细胞周期。我们认为上皮细胞影响I细胞中SRF的表达，从而影响I细胞进入分化途径的决定。
