Huang D, Chen S W, Langston A W, Gudas L J
Department of Pharmacology, Cornell University Medical College, New York, NY 10021, USA.
Development. 1998 Aug;125(16):3235-46. doi: 10.1242/dev.125.16.3235.
The murine Hoxb-1 gene contains a homeobox sequence and is expressed in a spatiotemporal specific pattern in neuroectoderm, mesoderm and gut endoderm during development. We previously identified a conserved retinoic acid (RA)-inducible enhancer, named the RAIDR5, which contains a DR5 RARE; this RAIDR5 enhancer is located 3' of the Hoxb-1-coding region in both the mouse and chick. In the F9 murine teratocarcinoma cell line, this DR5 RARE is required for the RA response of the Hoxb-1 gene, suggesting a functional role of the DR5 RARE in Hoxb-1 gene expression during embryogenesis. From the analysis of Hoxb-1/lacZ reporter genes in transgenic mice, we have shown that a wild-type (WT) transgene with 15 kb of Hoxb-1 genomic DNA, including this Hoxb-1 3' RAIDR5, is expressed in the same tissues and at the same times as the endogenous Hoxb-1 gene. However, a transgene construct with point mutations in the DR5 RARE (DR5mu) was not expressed in the developing foregut, which gives rise to organs such as the esophagus, lung, stomach, liver and pancreas. Like the wild-type transgene, this DR5 RARE mutated transgene was expressed in rhombomere 4 in 9.5 day postcoitum (d.p.c.) embryos. Similarly, transgene staining in the foregut of animals carrying a deletion of the entire Hox-b1 RAIDR5 enhancer (3'-del) was greatly reduced relative to that seen with the WT transgene. We also demonstrated that expression of the WT transgene in the gut increases in response to exogenous RA, resulting in anterior expansion of the expression in the gut. These observations that the Hoxb-1 gene is expressed in the developing gut and that this expression is regulated through a DR5 RARE strongly suggest a role for Hoxb-1 in the anteroposterior axis patterning of the gut and a critical role for endogenous retinoids in early gut development.
小鼠Hoxb - 1基因包含一个同源异型框序列，在发育过程中于神经外胚层、中胚层和肠内胚层以时空特异性模式表达。我们之前鉴定出一个保守的视黄酸（RA）诱导增强子，命名为RAIDR5，它包含一个DR5视黄酸反应元件（RARE）；这个RAIDR5增强子在小鼠和鸡中都位于Hoxb - 1编码区的3'端。在F9小鼠畸胎瘤细胞系中，这个DR5 RARE是Hoxb - 1基因对RA反应所必需的，这表明DR5 RARE在胚胎发生过程中对Hoxb - 1基因表达具有功能性作用。通过对转基因小鼠中Hoxb - 1 / lacZ报告基因的分析，我们已经表明，带有15 kb Hoxb - 1基因组DNA的野生型（WT）转基因，包括这个Hoxb - 1 3' RAIDR5，与内源性Hoxb - 1基因在相同组织和相同时间表达。然而，一个在DR5 RARE中具有点突变的转基因构建体（DR5mu）在前肠发育过程中不表达，前肠会发育出诸如食管、肺、胃、肝脏和胰腺等器官。与野生型转基因一样，这个DR5 RARE突变的转基因在妊娠9.5天（d.p.c.）胚胎的菱脑节4中表达。同样，相对于WT转基因，携带整个Hox - b1 RAIDR5增强子缺失（3'-del）的动物前肠中的转基因染色大大减少。我们还证明，WT转基因在肠道中的表达对外源RA有反应而增加，导致肠道中表达的前部扩展。这些关于Hoxb - 1基因在发育中的肠道中表达且这种表达通过DR5 RARE调节的观察结果，强烈暗示Hoxb - 1在肠道前后轴模式形成中起作用，以及内源性视黄酸在早期肠道发育中起关键作用。
