Genome-wide analysis of E17.5 pituitary gland gene expression of control and Insm1 mutant mice

The Insm1 gene encodes a zinc finger factor expressed in many endocrine organs. We show here that Insm1 is required for differentiation of all endocrine cell types in the pituitary. Thus, in Insm1 mutant mice, hormones characteristic of the different pituitary cell types (thyroid, follicle and melanocyte stimulating hormone, adrenocorticotrope hormone, growth hormone and prolactin) are absent or produced at markedly reduced levels. The differentiation deficit is accompanied by an up-regulated expression of components of the Notch signaling pathway. Further, skeletal muscle-specific genes are ectopically expressed, indicating that Insm1 blocks a muscle-specific expression program. Since Insm1 is also essential for differentiation of endocrine cells in the pancreas, intestine and adrenal gland, it is emerging as a transcription factor that acts in a pan-endocrine manner. The Insm1 factor contains a SNAG domain at its N-terminus, and we show here that the SNAG domain recruits histone modifying factors (Kdm1a, Hdac1/2 and Rcor1-3) and other proteins implicated in transcriptional regulation (Hmg20a/b and Gse1). Deletion of the SNAG domain in mice disrupted differentiation of pituitary endocrine cells, and resulted in an upregulated expression of components of the Notch signaling pathway and ectopic expression of skeletal muscle-specific genes. Our work demonstrates that Insm1 acts in the transcriptional network that controls differentiation of endocrine cells in the anterior pituitary gland, and requires the SNAG domain to exert this function in vivo. Analysis of genes regulated by Insm1 in embryonic day 17.5 pituitary gland. Total RNA from pituitary glands of E17.5 control embryos was compared to E17.5 Insm1 mutant embryos.胰岛素瘤相关1基因（Insm1）编码一种在多种内分泌器官中表达的锌指因子（zinc finger factor）。本研究证实，Insm1基因对于垂体中所有内分泌细胞类型的分化是必需的。因此，在Insm1突变小鼠体内，不同垂体细胞类型的标志性激素（促甲状腺激素、促卵泡激素、促黑素细胞激素、促肾上腺皮质激素、生长激素及催乳素）要么完全缺失，要么表达水平显著降低。该分化缺陷同时伴随Notch信号通路（Notch signaling pathway）组分的表达上调。此外，骨骼肌特异性基因出现异位表达，这表明Insm1能够抑制肌肉特异性表达程序。鉴于Insm1同样对胰腺、肠道及肾上腺中的内分泌细胞分化至关重要，该基因正逐渐被认定为一种以泛内分泌方式发挥功能的转录因子。Insm1蛋白的N端含有一个SNAG结构域，本研究证实该结构域能够招募组蛋白修饰因子（Kdm1a、Hdac1/2及Rcor1-3）以及其他参与转录调控的蛋白（Hmg20a/b与Gse1）。在小鼠体内删除SNAG结构域会破坏垂体内分泌细胞的分化，并导致Notch信号通路组分的表达上调以及骨骼肌特异性基因的异位表达。本研究证明，Insm1参与调控垂体前叶内分泌细胞分化的转录网络，且在体内发挥该功能时依赖于SNAG结构域。本研究对胚胎期17.5天的垂体中受Insm1调控的基因进行了分析：将E17.5天对照胚胎的垂体总RNA与同胎龄Insm1突变胚胎的垂体总RNA进行了对比。