Chojnowski Jena L, Masuda Kyoko, Trau Heidi A, Thomas Kirk, Capecchi Mario, Manley Nancy R
Department of Genetics, Paul D. Coverdell Center, 500 DW Brooks Drive, University of Georgia, Athens, GA 30602, USA.
Division of Hematology and Program in Molecular Medicine, University of Utah School of Medicine, Salt Lake City, UT 84132, USA.
Development. 2014 Oct;141(19):3697-708. doi: 10.1242/dev.110833. Epub 2014 Sep 5.
Hoxa3 was the first Hox gene to be mutated by gene targeting in mice and is required for the development of multiple endoderm and neural crest cell (NCC)-derived structures in the pharyngeal region. Previous studies have shown that the Hoxa3 null mutant lacks third pharyngeal pouch derivatives, the thymus and parathyroids by E18.5, and organ-specific markers are absent or downregulated during initial organogenesis. Our current analysis of the Hoxa3 null mutant shows that organ-specific domains did undergo initial patterning, but the location and timing of key regional markers within the pouch, including Tbx1, Bmp4 and Fgf8, were altered. Expression of the parathyroid marker Gcm2 was initiated but was quickly downregulated and differentiation failed; by contrast, thymus markers were delayed but achieved normal levels, concurrent with complete loss through apoptosis. To determine the cell type-specific roles of Hoxa3 in third pharyngeal pouch development, we analyzed tissue-specific mutants using endoderm and/or NCC-specific Cre drivers. Simultaneous deletion with both drivers resulted in athymia at E18.5, similar to the null. By contrast, the individual tissue-specific Hoxa3 deletions resulted in small, ectopic thymi, although each had a unique phenotype. Hoxa3 was primarily required in NCCs for morphogenesis. In endoderm, Hoxa3 temporally regulated initiation of the thymus program and was required in a cell-autonomous manner for parathyroid differentiation. Furthermore, Hoxa3 was required for survival of third pharyngeal pouch-derived organs, but expression in either tissue was sufficient for this function. These data show that Hoxa3 has multiple complex and tissue-specific functions during patterning, differentiation and morphogenesis of the thymus and parathyroids.
Hoxa3是第一个通过基因打靶在小鼠中发生突变的Hox基因，是咽区多个内胚层和神经嵴细胞（NCC）衍生结构发育所必需的。先前的研究表明，Hoxa3基因敲除突变体在E18.5时缺乏第三咽囊衍生物、胸腺和甲状旁腺，并且在初始器官发生过程中器官特异性标志物缺失或下调。我们目前对Hoxa3基因敲除突变体的分析表明，器官特异性结构域确实经历了初始模式形成，但囊内关键区域标志物（包括Tbx1、Bmp4和Fgf8）的位置和时间发生了改变。甲状旁腺标志物Gcm2的表达开始启动，但很快下调且分化失败；相比之下，胸腺标志物的表达延迟但达到正常水平，同时通过凋亡完全消失。为了确定Hoxa3在第三咽囊发育中细胞类型特异性的作用，我们使用内胚层和/或NCC特异性Cre驱动因子分析了组织特异性突变体。与两个驱动因子同时缺失导致E18.5时无胸腺，类似于基因敲除突变体。相比之下，单个组织特异性Hoxa3缺失导致小的异位胸腺，尽管每个都有独特的表型。Hoxa3主要在NCC中参与形态发生。在内胚层中，Hoxa3在时间上调节胸腺程序的启动，并且以细胞自主方式参与甲状旁腺分化。此外，Hoxa3是第三咽囊衍生器官存活所必需的，但在任何一种组织中的表达对于该功能都是足够的。这些数据表明，Hoxa3在胸腺和甲状旁腺的模式形成、分化和形态发生过程中具有多种复杂的组织特异性功能。
