Nishikawa A, Hayashi H
Department of Biological Science, Faculty of Life and Environmental Science, Shimane University, Japan.
Histochem Cell Biol. 1999 Apr;111(4):325-34. doi: 10.1007/s004180050364.
The conversion of an erythropoietic system from larval to adult type in anuran amphibia may possibly come about through cell replacement. The hormonal regulation of apoptosis of larval-type precursor cells and adult-type cell proliferation has yet to be examined in detail. In amphibians, corticoids synergize T3 action during metamorphosis. In the present study, examination was made of the process of larval-to-adult conversion in the liver erythropoietic site of Xenopus laevis, with special attention to how these metamorphic hormones, T3 and corticoid, regulate programmed cell death specific for larval erythroblasts and the proliferation of adult cells. Immunohistochemical analysis of liver sections indicates that the number of larval erythroblasts decreased to less than 50% at the early climax stage (stages 59-60) of metamorphosis. Overall liver morphology greatly changed subsequent to the climax stage from the three-lobe to the two-lobe shape. The addition of T3 (10(-8) M) to premetamorphic tadpoles induced considerable liver morphological change and a 50% decrease in larval-type erythroblasts. These erythroblast decreases seem to take place through the apoptotic process, since double-staining experiments with in situ DNA nick-end labeling (TUNEL) and hemoglobin immunostaining revealed that DNA breakage of nuclei, a well-known feature of apoptosis, occurred specifically in larval erythroblasts during prometamorphosis. Hydrocortisone (HC), which modulates T3 action during metamorphosis, was found not to be a factor in larval cell decrease. But adult erythroblasts increased by 8 times as much through the action of T3 and 32 times as much by the action of T3 plus HC, indicating the important action of T3-HC synergism. It thus follows that the erythropoietic system is converted during metamorphosis effectively by two distinct hormonal mechanisms, T3-HC synergism on adult erythroblast proliferation and T3-mediated programmed death of larval precursor cells.
无尾两栖动物的红细胞生成系统从幼体类型向成体类型的转变可能是通过细胞替代实现的。幼体型前体细胞凋亡和成体型细胞增殖的激素调节尚未得到详细研究。在两栖动物中，皮质类固醇在变态过程中协同T3发挥作用。在本研究中，对非洲爪蟾肝脏红细胞生成部位从幼体到成体的转变过程进行了研究，特别关注这些变态激素T3和皮质类固醇如何调节幼体红细胞特异性的程序性细胞死亡以及成体细胞的增殖。肝脏切片的免疫组织化学分析表明，在变态早期高潮阶段（第59 - 60阶段），幼体红细胞数量减少至不到50%。高潮阶段之后，肝脏整体形态从三叶形大幅转变为两叶形。将T3（10(-8) M）添加到变态前的蝌蚪中会引起肝脏形态的显著变化以及幼体型红细胞数量减少50%。这些红细胞数量的减少似乎是通过凋亡过程发生的，因为原位DNA缺口末端标记（TUNEL）和血红蛋白免疫染色的双重染色实验表明，细胞核DNA断裂这一凋亡的典型特征在变态前期特异性地发生在幼体红细胞中。发现氢化可的松（HC）在变态过程中调节T3的作用，但不是幼体细胞减少的一个因素。但是，通过T3的作用，成体红细胞增加了8倍，通过T3加HC的作用增加了32倍，表明T3 - HC协同作用的重要作用。因此可以得出结论，在变态过程中，红细胞生成系统通过两种不同的激素机制有效地转变，即T3 - HC对成体红细胞增殖的协同作用以及T3介导的幼体前体细胞程序性死亡。
