Kajioka Daiki, Suzuki Kentaro, Nakada Shoko, Matsushita Shoko, Miyagawa Shinichi, Takeo Toru, Nakagata Naomi, Yamada Gen
Department of Developmental Genetics, Institute of Advanced Medicine, Wakayama Medical University, Wakayama, Japan.
Division of Reproductive Engineering, Center for Animal Resources and Development, Kumamoto University, Kumamoto, Japan.
Congenit Anom (Kyoto). 2020 Jan;60(1):15-21. doi: 10.1111/cga.12326. Epub 2019 Feb 17.
The external genitalia are appendage organs outgrowing from the posterior body trunk. Murine genital tubercle (GT), anlage of external genitalia, initiates its outgrowth from embryonic day (E) 10.5 as a bud structure. Several growth factors such as fibroblast growth factor (FGF), Wnt and Sonic hedgehog (Shh) are essential for the GT outgrowth. However, the mechanisms of initiation of GT outgrowth are poorly understood. We previously identified bone morphogenetic protein (Bmp) signaling as a negative regulator for GT outgrowth. We show here novel aspects of Bmp4 functions for GT outgrowth. We identified the Bmp4 was already expressed in cloaca region at E9.5, before GT outgrowth. To analyze the function of Bmp4 at early stage for the initiation of GT outgrowth, we utilized the Hoxa3-Cre driver and Bmp4 mouse lines. Hoxa3 ; Bmp4 mutant mice showed the hypoplasia of GT with reduced expression of outgrowth promoting genes such as Wnt5a, Hoxd13 and p63, whereas Shh expression was not affected. Formation of distal urethral epithelium (DUE) marked by the Fgf8 expression is essential for controlling mesenchymal genes expression in GT and subsequent its outgrowth. Furthermore, Fgf8 expression was dramatically reduced in such mutant mice indicating the defective DUE formation. Hence, current results indicate that Bmp4 is an essential growth factor for the initiation of GT outgrowth independent of Shh signaling. Thus, Bmp4 positively regulates for the formation of DUE. The current study provides new insights into the function of Bmp signaling at early stage for the initiation of GT outgrowth.
外生殖器是从身体后躯干长出的附属器官。小鼠生殖结节（GT）作为外生殖器的原基，在胚胎第10.5天（E10.5）以芽状结构开始生长。几种生长因子，如成纤维细胞生长因子（FGF）、Wnt和音猬因子（Shh）对GT的生长至关重要。然而，GT生长起始的机制仍知之甚少。我们之前鉴定出骨形态发生蛋白（Bmp）信号传导是GT生长的负调节因子。我们在此展示了Bmp4在GT生长中的新功能。我们发现Bmp4在GT生长之前的E9.5就已在泄殖腔区域表达。为了分析Bmp4在GT生长起始早期的功能，我们利用了Hoxa3-Cre驱动小鼠品系和Bmp4条件性敲除小鼠品系。Hoxa3;Bmp4双突变小鼠表现出GT发育不全，促进生长的基因如Wnt5a、Hoxd13和p63的表达降低，而Shh的表达未受影响。以Fgf8表达为标志的远端尿道上皮（DUE）的形成对于控制GT中的间充质基因表达及其随后的生长至关重要。此外，在这种突变小鼠中Fgf8表达显著降低，表明DUE形成存在缺陷。因此，目前的结果表明Bmp4是GT生长起始所必需的生长因子，独立于Shh信号传导。因此，Bmp4正向调节DUE的形成。本研究为Bmp信号传导在GT生长起始早期的功能提供了新的见解。
