Requirement for Shh and Fox family genes at different stages in sweat gland development (E16.5)

Sweat glands play a fundamental role in thermal regulation in man, but the molecular mechanism of their development remains unknown. To initiate analyses, we compared the model of Eda mutant Tabby mice, in which sweat glands were not formed, to wild-type mice. We inferred developmental stages and critical genes based on observations at 7 time points spanning embryonic, postnatal and adult life. In wild-type footpads, sweat gland germs were detected at E17.5. The coiling of secretory portions started at postnatal day 1 (P1), and sweat gland formation was essentially complete by P5. Consistent with a controlled morphological progression, expression profiling revealed stage-specific gene expression changes. Similar to the development of hair follicles the other major skin appendage controlled by EDA sweat gland induction and initial progression was accompanied by Eda-dependent up-regulation of the Shh pathway. During the further development of sweat gland secretory portions, Foxa1 and Foxi1, not at all expressed in hair follicles, were progressively up-regulated in wild-type but not in Tabby footpads. Upon completion of wild-type development, Shh declined to Tabby levels, but Fox family genes remained at elevated levels in mature sweat glands. The results provide a framework for the further analysis of phased downstream regulation of gene action, possibly by a signaling cascade, in response to Eda. Keywords: cell type comparison design,development or differentiation design To define target genes of Eda during sweat gland development, we carried out microarray experiments with mouse footpads that from 7 developmental time points including E15.5, E16.5, E17.5, P1, P3, P5 and 8 weeks of wild-type and Tabby mice. This dataset is E16.5.汗腺在人类体温调节中发挥着核心作用，但其发育的分子机制至今仍未明确。为启动相关研究，我们将汗腺发育完全缺失的外异蛋白A（Ectodysplasin A, Eda）突变Tabby小鼠模型与野生型小鼠进行对比。本研究基于覆盖胚胎期、出生后及成年阶段的7个时间点的观测数据，推断汗腺发育的阶段特征与关键基因。 在野生型小鼠足垫中，于胚胎第17.5天（E17.5）可检测到汗腺原基；分泌段的卷曲过程始于出生后第1天（P1），至出生后第5天（P5）时汗腺形成基本完成。与受控的形态发生进程一致，表达谱分析显示存在阶段特异性的基因表达变化。 与另一种受EDA调控的主要皮肤附属器——毛囊的发育过程相似，汗腺的诱导与初始发育进程，均伴随有Eda依赖的Sonic Hedgehog（Shh）信号通路上调。在汗腺分泌段的进一步发育过程中，在毛囊中完全不表达的Foxa1与Foxi1基因，在野生型小鼠足垫中呈渐进式上调，而在Tabby小鼠足垫中则未出现该表达变化。当野生型小鼠汗腺发育完成时，Shh的表达水平下调至与Tabby小鼠一致的水平，但Fox家族基因在成熟汗腺中仍维持较高表达水平。 本研究结果为解析EDA响应下、可能通过信号级联反应实现的分阶段下游基因调控机制，提供了系统性的研究框架。 关键词：细胞类型比较设计、发育或分化设计 为明确汗腺发育过程中EDA的靶基因，我们针对野生型与Tabby小鼠的足垫样本开展了基因芯片（microarray）实验，样本覆盖7个发育时间点：E15.5、E16.5、E17.5、P1、P3、P5及8周龄。本数据集对应时间点为E16.5。