Dupé V, Ghyselinck N B, Thomazy V, Nagy L, Davies P J, Chambon P, Mark M
Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), CNRS/INSERM/ULP/ Collège de France, Illkirch Cedex, C.U de Strasbourg, 67404, France.
Dev Biol. 1999 Apr 1;208(1):30-43. doi: 10.1006/dbio.1998.9176.
We previously reported that mice lacking the RARgamma gene and one or both alleles of the RARbeta gene (i.e., RARbeta+/-/RARgamma-/- and RARbeta-/-/RARgamma-/- mutants) display a severe and fully penetrant interdigital webbing (soft tissue syndactyly), caused by the persistence of the fetal interdigital mesenchyme (Ghyselinck et al., 1997, Int. J. Dev. Biol. 41, 425-447). In the present study, these compound mutants were used to investigate the cellular and molecular mechanisms involved in retinoic acid (RA)-dependent formation of the interdigital necrotic zones (INZs). The mutant INZs show a marked decrease in the number of apoptotic cells accompanied by an increase of cell proliferation. This marked decrease was not paralleled by a reduction of the number of macrophages, indicating that the chemotactic cues which normally attract these cells into the INZs were not affected. The expression of a number of genes known to be involved in the establishment of the INZs, the patterning of the autopod, and/or the initiation of apoptosis was also unaffected. These genes included BMP-2, BMP-4, Msx-1, Msx-2, 5' members of Hox complexes, Bcl2, Bax, and p53. In contrast, the mutant INZs displayed a specific, graded, down-regulation of tissue transglutaminase (tTG) promoter activity and of stromelysin-3 expression upon the removal of one or both alleles of the RARbeta gene from the RARgamma null genetic background. As retinoic acid response elements are present in the promoter regions of both tTG and stromelysin-3 genes, we propose that RA might increase the amount of cell death in the INZs through a direct modulation of tTG expression and that it also contributes to the process of tissue remodeling, which accompanies cell death, through an up-regulation of stromelysin-3 expression in the INZs. Approximately 10% of the RARbeta-/- /RARgamma-/- mutants displayed a supernumerary preaxial digit on hindfeet, which is also a feature of the BMP-7 null phenotype (Dudley et al., 1995, Genes Dev. 9, 2795-2807; Luo et al., 1995, Genes Dev. 9, 2808-2820). BMP-7 was globally down-regulated at an early stage in the autopods of these RAR double null mutants, prior to the appearance of the digital rays. Therefore, RA may exert some of its effects on anteroposterior autopod patterning through controlling BMP-7 expression.
我们之前报道过，缺乏视黄酸受体γ（RARγ）基因以及视黄酸受体β（RARβ）基因一个或两个等位基因的小鼠（即RARβ+/-/RARγ-/-和RARβ-/-/RARγ-/-突变体）表现出严重且完全显性的指间蹼（软组织并指），这是由胎儿指间间充质持续存在所致（吉瑟林克等人，1997年，《国际发育生物学杂志》41卷，425 - 447页）。在本研究中，这些复合突变体被用于研究参与视黄酸（RA）依赖性指间坏死区（INZ）形成的细胞和分子机制。突变体的INZ显示凋亡细胞数量显著减少，同时细胞增殖增加。这种显著减少与巨噬细胞数量的减少并不平行，这表明正常吸引这些细胞进入INZ的趋化信号未受影响。一些已知参与INZ形成、肢体末端模式形成和/或凋亡起始的基因的表达也未受影响。这些基因包括骨形态发生蛋白 - 2（BMP - 2）、骨形态发生蛋白 - 4（BMP - 4）、肌节同源盒基因 - 1（Msx - 1）、肌节同源盒基因 - 2（Msx - 2）、Hox复合体的5'成员、Bcl2、Bax和p53。相反，当从RARγ基因缺失的遗传背景中去除RARβ基因的一个或两个等位基因时，突变体的INZ在组织转谷氨酰胺酶（tTG）启动子活性和基质溶解素 - 3表达方面呈现出特异性的、分级的下调。由于tTG和基质溶解素 - 3基因的启动子区域都存在视黄酸反应元件，我们推测RA可能通过直接调节tTG表达来增加INZ中的细胞死亡数量，并且它还通过上调INZ中基质溶解素 - 3的表达，促进伴随细胞死亡的组织重塑过程。大约10%的RARβ-/- /RARγ-/-突变体后足出现额外的前轴趾，这也是BMP - 7基因缺失表型的一个特征（达德利等人，1995年，《基因与发育》9卷，2795 - 2807页；罗等人，1995年，《基因与发育》9卷，2808 - 2820页）。在这些RAR双基因缺失突变体的肢体末端，数字射线出现之前的早期阶段，BMP - 7整体下调。因此，RA可能通过控制BMP - 7的表达，对前后轴肢体末端模式形成发挥一些作用。
