Berry D L, Schwartzman R A, Brown D D
Department of Embryology, Carnegie Institution of Washington, Baltimore, Maryland, 21210, USA.
Dev Biol. 1998 Nov 1;203(1):12-23. doi: 10.1006/dbio.1998.8974.
Expression of genes up-regulated by thyroid hormone (TH) during amphibian tail resorption was localized by in situ hybridization. The constitutive thyroid hormone receptor (TRalpha) and its heterodimeric partners (RXRalpha and RXRbeta) are expressed ubiquitously in the resorbing tail. A group of early response genes, including those encoding transcription factors, are expressed at greatest levels within tissues whose cells attempt to grow and differentiate in the tail, but eventually succumb to the resorption program. The TH-inducible TR isoform, TRbeta, is expressed ubiquitously in the tail, but especially high in fibroblasts. Similarly, a group of delayed response genes including two proteolytic enzymes that appear to execute the tail resorption program, is expressed specifically in fibroblasts that line and surround the notochord and lie beneath the epidermal lamella (subepidermal fibroblasts). During active tail resorption these fibroblasts invade their neighboring epidermal and notochord lamellae as part of the resorption process. Expression analysis implicates the single layer of invasive subepidermal fibroblasts as crucial in tail resorption. Stromelysin-3 is up-regulated by TH with early kinetics, and is expressed most actively in fibroblasts within the tail fins. None of the proteases are expressed in the tadpole epidermis, which will be replaced entirely during metamorphosis. While very few TH response genes are expressed in tadpole muscle, many are activated in fibroblasts that surround muscle and could induce muscle cell death by proteolysis of the extracellular matrix. These distinct localization patterns suggest that the common fate of all cell types within the tail is the result of multiple genetic programs.
通过原位杂交确定了甲状腺激素（TH）在两栖动物尾部吸收过程中上调的基因的表达情况。组成型甲状腺激素受体（TRα）及其异源二聚体伙伴（RXRα和RXRβ）在吸收的尾部广泛表达。一组早期反应基因，包括那些编码转录因子的基因，在尾部细胞试图生长和分化但最终屈服于吸收程序的组织中表达水平最高。TH诱导型TR异构体TRβ在尾部广泛表达，但在成纤维细胞中表达尤其高。同样，一组延迟反应基因，包括两种似乎执行尾部吸收程序的蛋白水解酶，特异性地在围绕脊索并位于表皮薄片下方的成纤维细胞（表皮下成纤维细胞）中表达。在活跃的尾部吸收过程中，这些成纤维细胞侵入其相邻的表皮和脊索薄片，作为吸收过程的一部分。表达分析表明，单层侵袭性表皮下成纤维细胞在尾部吸收中至关重要。基质溶解素-3被TH以早期动力学上调，并在尾鳍内的成纤维细胞中最活跃地表达。没有一种蛋白酶在蝌蚪表皮中表达，蝌蚪表皮在变态过程中会完全被替换。虽然在蝌蚪肌肉中表达的TH反应基因很少，但许多基因在围绕肌肉的成纤维细胞中被激活，并可能通过细胞外基质的蛋白水解诱导肌肉细胞死亡。这些不同的定位模式表明，尾部所有细胞类型的共同命运是多个遗传程序的结果。
