Shannon J M
Department of Medicine, Denver, Colorado.
Dev Biol. 1994 Dec;166(2):600-14. doi: 10.1006/dbio.1994.1340.
Normal branching morphogenesis and cytodifferention of the lung require a specific interaction between the epithelial rudiment and pulmonary mesenchyme. Previous studies in the mouse have shown glandular stage pulmonary mesenchyme can elicit a lung-like pattern of branching morphogenesis when grafted onto tracheal epithelium of the same age that has been denuded of its own mesenchyme. We have examined whether are not this pattern of branching is accompanied by changes in epithelial cytodifferentiation. Purified pulmonary mesenchyme was isolated from the distal tips of day 13-14 fetal rat lungs and grafted onto a stretch of tracheal epithelium from which the mesenchyme had been removed. The grafts were cultured on semisolid 0.5% agarose in Waymouth's medium containing 10% serum for 5 days and then for an additional 2 days in the same medium containing 10(-6) M cortisol. Unoperated or operated-ungrafted tracheae and intact lung explants served as controls. Grafting distal tip pulmonary mesenchyme onto the tracheal epithelium induced a pattern of branching identical to that seen in control lung explant cultures, while ungrafted control tracheal cultures formed cystic structures. Light microscopy of the induced tracheal epithelium showed that the constituent cells exhibited a morphology virtually identical to cells in control lung explants. Ultrastructural analysis demonstrated that the induced tracheal epithelial cells contained lamellar inclusion bodies, and the lumina of the induced acinar structures contained tubular myelin figures. Reverse transcription polymerase chain reaction analysis of the induced tracheae revealed the presence of mRNAs for surfactant protein A (SP-A) and SP-B, as well as SP-C, which is a specific marker for type II cell differentiation in the adult rat. Control tracheal cultures contained mRNAs only for SP-A and SP-B. Immunocytochemistry demonstrated that many cells within the induced tracheal epithelium were positive for SP-A and SP-C proteins. Further studies demonstrated that the ability of mesenchyme to induce tracheal epithelium varied within the pulmonary tree, and that the competence of the tracheal epithelium to respond to the influence of distal tip mesenchyme was temporally restricted. Our results demonstrate that pulmonary mesenchyme can act instructively on the tracheal epithelium to induce a program of type II cell differentiation.
肺的正常分支形态发生和细胞分化需要上皮原基与肺间充质之间的特定相互作用。先前在小鼠中的研究表明，腺泡期肺间充质移植到已去除自身间充质的同龄气管上皮上时，可引发类似肺的分支形态发生模式。我们研究了这种分支模式是否伴随着上皮细胞分化的变化。从第13 - 14天胎鼠肺的远端分离纯化的肺间充质，并移植到一段已去除间充质的气管上皮上。将移植物在含10%血清的Waymouth培养基中的半固体0.5%琼脂糖上培养5天，然后在含10(-6)M皮质醇的相同培养基中再培养2天。未手术或手术未移植的气管以及完整的肺外植体作为对照。将远端肺间充质移植到气管上皮上诱导出与对照肺外植体培养中所见相同的分支模式，而未移植的对照气管培养形成囊性结构。诱导的气管上皮的光学显微镜检查显示，组成细胞的形态与对照肺外植体中的细胞几乎相同。超微结构分析表明，诱导的气管上皮细胞含有板层包涵体，诱导的腺泡结构的管腔含有管状髓磷脂样结构。对诱导的气管进行逆转录聚合酶链反应分析发现存在表面活性蛋白A（SP - A）、SP - B以及SP - C的mRNA，SP - C是成年大鼠II型细胞分化的特异性标志物。对照气管培养物仅含有SP - A和SP - B的mRNA。免疫细胞化学表明，诱导的气管上皮内的许多细胞对SP - A和SP - C蛋白呈阳性。进一步研究表明，间充质诱导气管上皮的能力在肺树内有所不同，并且气管上皮对远端间充质影响的反应能力在时间上受到限制。我们的结果表明，肺间充质可对气管上皮起诱导作用，以诱导II型细胞分化程序。
