Herman R K, Hedgecock E M
Department of Genetics and Cell Biology, University of Minnesota, St Paul 55108.
Nature. 1990 Nov 8;348(6297):169-71. doi: 10.1038/348169a0.
In the nematode Caenorhabditis elegans six hypodermal cells, the vulval precursor cells, are each competent to generate vulval cells. Normally only the three nearest precursor cells to the uterine anchor cell generate the vulva (22 nuclei), while the three others fuse with the non-specialized hypodermal syncytium (hyp7) surrounding each precursor cell and covering the body. Without an inductive signal from the anchor cell, all six vulval precursor cells fuse with hyp7 and no vulva is formed. But without activity of the vulval determination gene lin-15(+), all six cells undergo vulval divisions whether the anchor cell is present or not. Using mosaic analysis, we demonstrate here that lin-15(+) expression is necessary in cells other than the vulval precursor cells or the anchor cell, most probably in the hyp7 syncytium. We propose that lin-15(+) is active in hyp7 in order to repress an intrinsic vulval program in the precursor cells. The inductive signal from the anchor cell counteracts this repression for three precursor cells, allowing them to generate vulval cells. Such a two-signal (repressor/derepressor) mechanism may operate in other cases of tissue induction.
在线虫秀丽隐杆线虫中，六个皮下细胞，即外阴前体细胞，每个都有能力产生外阴细胞。正常情况下，只有最靠近子宫锚定细胞的三个前体细胞产生外阴（22个细胞核），而另外三个则与围绕每个前体细胞并覆盖身体的非特化皮下合胞体（hyp7）融合。没有来自锚定细胞的诱导信号，所有六个外阴前体细胞都会与hyp7融合，不会形成外阴。但是，如果没有外阴决定基因lin-15(+)的活性，无论锚定细胞是否存在，所有六个细胞都会进行外阴分裂。通过镶嵌分析，我们在此证明lin-15(+)的表达在外阴前体细胞或锚定细胞以外的细胞中是必需的，很可能在hyp7合胞体中。我们提出lin-15(+)在hyp7中是活跃的，以便抑制前体细胞中的内在外阴程序。来自锚定细胞的诱导信号抵消了三个前体细胞的这种抑制作用，使它们能够产生外阴细胞。这种双信号（阻遏物/去阻遏物）机制可能在其他组织诱导情况下起作用。
