Towers P R, Woolf A S, Hardman P
Developmental Biology Unit, University College London, UK.
Exp Nephrol. 1998 Jul-Aug;6(4):337-51. doi: 10.1159/000020541.
Development of epithelial organs requires co-ordinated interactions between epithelial and mesenchymal tissues. Studies using null mutant mice have indicated that the ret receptor and its ligand, glial cell line-derived neurotrophic factor (GDNF), are crucial for initiation of development of the metanephric kidney. However, the role of this signalling system in other branching organs has not been analysed. Here we describe expression studies of ret, GDNF, and a co-receptor for GDNF (GDNFR alpha) in the developing mouse metanephros, lung, and submandibular salivary gland. Also, we examined the role of this signalling system in the development of these organs in vitro. In situ hybridisation revealed differences in the spatial distribution of the three transcripts in the different organs. At the initiation of metanephric development, late on embryonic day 10 (E10), ret and GDNFR alpha were detected in the Wolffian duct (including the presumptive ureteric bud) whilst the presumptive metanephric, mesenchyme expressed GDNFR alpha and GDNF. Later in development, all three transcripts were restricted to the nephrogenic zone. In contrast, expression in the lung was not detectable by in situ hybridisation until after initiation of development, at E13.5. At this time ret was expressed throughout the epithelium; GDNF was detected throughout the mesenchyme, and GDNFR alpha was present in the proximal epithelium and mesenchyme only. Ret and GDNF were not detected in the epithelium or mesenchyme of the developing salivary gland, however, GDNFR alpha was expressed in the mesenchyme at E13.5 and E16.5. Functional studies demonstrated that in organ culture, GDNF significantly increased branching morphogenesis of the E11.5 metanephros, and induced the formation of ectopic ureteric buds from the base of the bud and from the Wolffian duct. The development of lung and salivary primordia were not affected under similar growth conditions. In a novel ureteric bud primary culture system, GDNF significantly increased cell numbers at 24 and 48 h. In cells cultured on laminin this increase was due to increased survival and proliferation, whereas in cells cultured on fibronectin, only survival was enhanced. Our data suggest that GDNF stimulates outgrowth of the ureteric bud, in part, by enhancing cell survival and possibly by increasing proliferation.
上皮器官的发育需要上皮组织和间充质组织之间的协调相互作用。利用基因敲除小鼠进行的研究表明，Ret受体及其配体胶质细胞系源性神经营养因子（GDNF）对于后肾发育的起始至关重要。然而，该信号系统在其他分支器官中的作用尚未得到分析。在此，我们描述了Ret、GDNF以及GDNF的共受体（GDNFRα）在发育中的小鼠后肾、肺和下颌下唾液腺中的表达研究。此外，我们在体外研究了该信号系统在这些器官发育中的作用。原位杂交显示这三种转录本在不同器官中的空间分布存在差异。在后肾发育起始时，即胚胎第10天晚期（E10），在中肾管（包括假定的输尿管芽）中检测到Ret和GDNFRα，而假定的后肾间充质表达GDNFRα和GDNF。在发育后期，所有三种转录本都局限于肾发生区。相比之下，直到发育起始后，即E13.5时，原位杂交才在肺中检测到表达。此时Ret在整个上皮中表达；GDNF在整个间充质中被检测到，而GDNFRα仅存在于近端上皮和间充质中。在发育中的唾液腺上皮或间充质中未检测到Ret和GDNF，然而，在E13.5和E16.5时，GDNFRα在间充质中表达。功能研究表明，在器官培养中，GDNF显著增加E11.5后肾的分支形态发生，并诱导从芽基部和中肾管形成异位输尿管芽。在类似的生长条件下，肺和唾液原基的发育不受影响。在一种新型的输尿管芽原代培养系统中，GDNF在24小时和48小时时显著增加细胞数量。在层粘连蛋白上培养的细胞中，这种增加是由于存活和增殖增加，而在纤连蛋白上培养的细胞中，仅存活得到增强。我们的数据表明，GDNF部分通过增强细胞存活并可能通过增加增殖来刺激输尿管芽的生长。
