Yee G W, Abbott U K
J Exp Zool. 1978 Dec;206(3):307-21. doi: 10.1002/jez.1402060302.
Early facial development in normal chick embryos was studied by scanning electron microscopy, and compared to the abnormal facial development of a mutant in which primary palate formation does not occur, thus resulting in bilateral cleft lip. In both normal and "cleft primary palate" mutant embryos, subsequent to the appearance of the nasal placodes, the surrounding tissues elevate to give rise to the presumptive facial primordia. As the facial primordia grow forward, they gradually assume the configuration of a square which is most pronounced at five days development. In normal embryos, the square configuration is then lost as the facial primordia become aligned in preparation for primary palate formation. The primary palate is formed at six days development by fusion of the "free-ended" medial nasal processes with the combined lateral nasal and maxillary processes across the nasal grooves. Just prior to fusion, long, slender filaments extend from the apposing surfaces of the facial primordia in the regions of prefusion contact. It is speculated that these "prefusion filaments" may function in alignment or adhesion of the facial primordia. In "cleft primary palate" embryos, facial morphogenesis appears to arrest at five days development, so that the square configuration persists. The medial nasal processes never contact the lateral nasal and maxillary processes, but instead remain separated from them by wide nasal grooves. Furthermore, facial primordia of mutant embryos do not exhibit the "prefusion filaments" characteristic of normal embryos.
通过扫描电子显微镜研究了正常鸡胚的早期面部发育，并将其与一种突变体的异常面部发育进行了比较，该突变体中不会发生原发腭形成，从而导致双侧唇裂。在正常和“原发腭裂”突变体胚胎中，鼻基板出现后，周围组织隆起形成假定的面部原基。随着面部原基向前生长，它们逐渐呈现出方形结构，在发育五天时最为明显。在正常胚胎中，随着面部原基排列整齐以准备形成原发腭，方形结构随后消失。原发腭在发育六天时由“自由端”的内侧鼻突与外侧鼻突和上颌突跨过鼻沟融合形成。就在融合之前，长而细的细丝从面部原基在融合前接触区域的相对表面延伸出来。据推测，这些“融合前细丝”可能在面部原基的排列或黏附中起作用。在“原发腭裂”胚胎中，面部形态发生似乎在发育五天时停止，因此方形结构持续存在。内侧鼻突从未与外侧鼻突和上颌突接触，而是被宽阔的鼻沟与它们隔开。此外，突变体胚胎的面部原基不表现出正常胚胎特有的“融合前细丝”。
