Marikawa Yusuke, Satoh Noriyuki
Department of Zoology, Graduate School of Science, Kyoto University, Kyoto 606-01 and Asamushi Marine Biological Station, Tohoku University, Aomori 039-34, Japan.
Dev Growth Differ. 1996 Apr;38(2):167-173. doi: 10.1046/j.1440-169X.1996.t01-1-00006.x.
The ascidian egg contains muscle and endoderm determinants that play critical roles in the specification of muscle and endoderm cells, respectively. Endoderm cells of the ascidian embryo express alkaline phosphatase (AP) as a tissue-specific enzyme. We obtained egg fragments from the unfertilized eggs of Ciona savignyi by means of centrifugal force. The largest fragment (red fragments) contained the egg nucleus while other small fragments (black, clear and brown fragments) were anucleate. When inseminated, only red fragments developed into partial embryos, which showed only epidermis cell differentiation and, very rarely, AP activity. When red fragments were fused with other fragments, only black fragments promoted AP expression, suggesting that endoderm determinants were concentrated in the black fragments. A lower dose (1500 J/m ) of ultraviolet (UV) light did not eliminate the AP-promoting ability of black fragments, while this dose significantly repressed the ability to promote the expression of the muscle-marker. A higher dose (4500 J/m ) of UV light markedly reduced the AP-promoting activity of black fragments. These results suggest that factors for endodermal AP development are inactivated by UV irradiation, but are more resistant than muscle determinants.
海鞘卵含有肌肉和内胚层决定因子，它们分别在肌肉细胞和内胚层细胞的特化过程中发挥关键作用。海鞘胚胎的内胚层细胞表达碱性磷酸酶（AP）作为一种组织特异性酶。我们通过离心力从未受精的萨氏海鞘卵中获得卵片段。最大的片段（红色片段）含有卵细胞核，而其他小片段（黑色、透明和棕色片段）无细胞核。受精时，只有红色片段发育成部分胚胎，这些胚胎仅表现出表皮细胞分化，且极少有AP活性。当红色片段与其他片段融合时，只有黑色片段促进AP表达，这表明内胚层决定因子集中在黑色片段中。较低剂量（1500 J/m ）的紫外线（UV）并未消除黑色片段促进AP表达的能力，而该剂量显著抑制了促进肌肉标记物表达的能力。较高剂量（4500 J/m ）的紫外线明显降低了黑色片段促进AP表达的活性。这些结果表明，内胚层AP发育的因子会被紫外线照射失活，但比肌肉决定因子更具抗性。
