Huber Katrin, Combs Stephanie, Ernsberger Uwe, Kalcheim Chaya, Unsicker Klaus
Department of Neuroanatomy, Interdisciplinary Center for Neurosciences, University of Heidelberg, Heidelberg, Germany.
Ann N Y Acad Sci. 2002 Oct;971:554-9. doi: 10.1111/j.1749-6632.2002.tb04526.x.
The developmental diversification of neural crest-derived sympathoadrenal (SA) progenitor cells into neuroendocrine adrenal chromaffin cells and sympathetic neurons has been thought to be largely understood. Based on two decades of in vitro studies with isolated SA progenitor and chromaffin cells, it was widely assumed that chromaffin cell development crucially depends on glucocorticoid hormones provided by adrenal cortical cells. However, analysis of mice lacking the glucocorticoid receptor has revealed that the chromaffin cell phenotype develops largely normally in these mice, except for the induction of the adrenaline synthesizing enzyme phenylethylamine N-methyl transferase. In a search for novel candidate genes that might be involved in triggering the sympathetic neuron/chromaffin cell decision, we have studied putative contributions of transforming growth factor (TGF)-alpha, BMP-4, and the transcription factor MASH-1, molecules with distinct expressions in SA progenitor cells, in their migratory pathways and final destinations. TGF-beta2 and -beta3 and BMP-4 are highly expressed in the wall of the dorsal aorta and in the adrenal anlagen during and after immigration of SA progenitors but expressed at much lower levels in sympathetic ganglia. We found that neutralizing antibodies against all three TGF-beta isoforms applied to the chorionic-allantoic membrane (CAM) of quail embryos interfere with proliferation of immigrated adrenal chromaffin cells but do not affect their specific neuroendocrine ultrastructural phenotype. Grafting of noggin-producing cells to the CAM, which scavenges BMPs, interferes with visceral arch and limb development but does not overtly affect the chromaffin phenotype. The transcription factor MASH-1 promotes early differentiation of SA progenitors. Mice deficient for MASH-1 lack sympathetic ganglia, whereas the adrenal medulla previously has been reported to be present. We show here that most adrenal medullary cells in MASH-1(-/-) mice identified by Phox2b immunoreactivity lack the catecholaminergic marker tyrosine hydroxylase. More surprisingly, most cells do not contain chromaffin granules and display a neuroblast-like ultrastructure and show strongly enhanced expression of c-RET comparable to that observed in sympathetic ganglia. Together, our data suggest that TGF-betas and BMP-4 do not seem to be essential for chromaffin cell differentiation. In contrast with previous reports, however, MASH-1 apparently plays a crucial role in chromaffin cell development.
神经嵴衍生的交感肾上腺（SA）祖细胞向神经内分泌肾上腺嗜铬细胞和交感神经元的发育分化在很大程度上已被认为是清楚的。基于对分离的SA祖细胞和嗜铬细胞进行的二十年体外研究，人们普遍认为嗜铬细胞的发育关键取决于肾上腺皮质细胞提供的糖皮质激素。然而，对缺乏糖皮质激素受体的小鼠的分析表明，除了肾上腺素合成酶苯乙胺N-甲基转移酶的诱导外，嗜铬细胞表型在这些小鼠中基本正常发育。在寻找可能参与触发交感神经元/嗜铬细胞分化决定的新候选基因的过程中，我们研究了转化生长因子（TGF）-α、骨形态发生蛋白（BMP）-4和转录因子MASH-1的假定作用，这些分子在SA祖细胞及其迁移途径和最终目的地有不同表达。TGF-β2和-β3以及BMP-4在SA祖细胞迁移期间和之后在背主动脉壁和肾上腺原基中高度表达，但在交感神经节中表达水平低得多。我们发现，应用于鹌鹑胚胎绒毛膜尿囊膜（CAM）的针对所有三种TGF-β同工型的中和抗体干扰了迁移的肾上腺嗜铬细胞的增殖，但不影响其特定的神经内分泌超微结构表型。将产生头蛋白的细胞移植到CAM上，该蛋白可清除BMP，会干扰内脏弓和肢体发育，但不会明显影响嗜铬细胞表型。转录因子MASH-1促进SA祖细胞的早期分化。缺乏MASH-1的小鼠没有交感神经节，而此前有报道称肾上腺髓质存在。我们在此表明，通过Phox2b免疫反应性鉴定的MASH-1（-/-）小鼠中的大多数肾上腺髓质细胞缺乏儿茶酚胺能标记物酪氨酸羟化酶。更令人惊讶的是，大多数细胞不含嗜铬颗粒，呈现成神经细胞样超微结构，并显示出与交感神经节中观察到的相当的c-RET表达强烈增强。总之，我们的数据表明TGF-β和BMP-4似乎对嗜铬细胞分化不是必需的。然而，与先前的报道相反，MASH-1显然在嗜铬细胞发育中起关键作用。
