Zhao Yangu, Morales Donna Chelle, Hermesz Edit, Lee Woon-Kyu, Pfaff Samuel L, Westphal Heiner
Laboratory of Mammalian Genes and Development, National Institute of Child Health and Human Development, Bethesda, MD 20892, USA.
Mech Dev. 2006 Aug;123(8):605-13. doi: 10.1016/j.mod.2006.06.005. Epub 2006 Jun 14.
The formation of the anterior and intermediate lobes of the pituitary gland is a multi-step process regulated by cell-cell interactions involving a number of signaling pathways and by cascades of cell-intrinsic transcription factors. The LIM-homeodoamin protein Lhx3 has previously been shown to play an essential role in the growth of Rathke's pouch, a primordium of the anterior and intermediate lobes of the pituitary. However, the mechanisms underlying the function and regulation of Lhx3 remain to be elucidated. Here we report that a targeted insertion of a DNA fragment in the 3'-untranslated region of the Lhx3 gene reduces the expression of both Lhx3 mRNA and protein in Rathke's pouch. Mutant mice homozygous for this Lhx3 allele show severe hypoplasia of the pouch, a defect identical to that observed in Lhx3-null mutants. To gain insights into the mechanism of Lhx3 function in pituitary development, we further analyzed the Lhx3 deficient mutants by examination of early pituitary marker expression, cell proliferation, and cell apoptosis. Our results revealed an increase in cell apoptosis and a loss of Islet1 and Calbindin marker expression in Rathke's pouch of these mutants. Recently, increased cell apoptosis in Rathke's pouch has been described in mutant mice impaired in the function of the bicoid-like homeodomain proteins Pitx1 and Pitx2. In those mutants, the expression of Lhx3 is absent. Our results thus underscore the view that Lhx3 functions downstream of the Pitx factors in the same transcriptional cascade that controls growth and early cell differentiation of the developing pituitary gland.
垂体前叶和中叶的形成是一个多步骤过程，受涉及多种信号通路的细胞间相互作用以及细胞内源性转录因子级联反应的调节。此前已证明，LIM同源结构域蛋白Lhx3在拉特克囊（垂体前叶和中叶的原基）的生长中起关键作用。然而，Lhx3功能和调控的潜在机制仍有待阐明。在此，我们报告在Lhx3基因的3'非翻译区靶向插入一个DNA片段会降低拉特克囊中Lhx3 mRNA和蛋白质的表达。纯合携带此Lhx3等位基因的突变小鼠表现出囊的严重发育不全，这一缺陷与在Lhx3基因敲除突变体中观察到的相同。为深入了解Lhx3在垂体发育中的功能机制，我们通过检测早期垂体标志物表达、细胞增殖和细胞凋亡，进一步分析了Lhx3缺陷型突变体。我们的结果显示，这些突变体的拉特克囊中细胞凋亡增加，胰岛1和钙结合蛋白标志物表达缺失。最近，在类双尾同源结构域蛋白Pitx1和Pitx2功能受损的突变小鼠中，已描述了拉特克囊中细胞凋亡增加的情况。在那些突变体中，Lhx3的表达缺失。因此，我们的结果强调了这样一种观点，即在控制发育中垂体的生长和早期细胞分化的同一转录级联反应中，Lhx3在Pitx因子的下游发挥作用。
