The development of the beak in turtles is poorly known. Beak development has been analyzed by immunofluorescent methods for studying cell proliferation and localization of specific proteins. The flat two-layered epidermis covering the turtle embryo at mid stage of development becomes columnar in the oral region and is associated with an increase of mesenchymal density as in placodes. Using 5BrdU, an intense cell proliferation is observed in the oral and epidermal cells covering the maxilla and mandibular bones, probably stimulated by the underlying mesenchyme in continuation with maxillary and mandibular bones. Expansion and fusion of these placodes give rise to the corneous beak. Beta catenin, mainly junctional but also sparsely detected in nuclei of the germinal layer of the beak epithelium, maintains united the differentiating keratinocytes that form a stratified corneous epithelium. This is initially composed of some layers of large cells that accumulate intermediate filament keratins (IFKs) and give rise to a keratinized embryonic epidermis destined to slough around hatching. The following corneocytes accumulate IFKs but mainly type I/II corneous beta proteins (CBPs) and form a corneous beak. These CBPs appear present with lower intensity in the beak than in the shell, but the higher intensity obtained with a general antibody against CBPs indicates that other CBPs contribute to the composition and stiffness of beak corneous material. The egg-tooth in continuation with the stratum corneum of the maxillary beak develops from a localized proliferation and comprises a thick embryonic epidermis accumulating IFKs under which large beta-cells connected by adhesion proteins accumulate CBPs contributing to hardening of this temporary organ.

中文翻译：

---

乌龟Emydura macquarii发育中的喙和卵齿中角质形成细胞的细胞增殖、粘附和分化

乌龟喙的发育鲜为人知。喙发育已通过免疫荧光方法进行分析，用于研究特定蛋白质的细胞增殖和定位。在发育中期覆盖龟胚的扁平两层表皮在口腔区域变成柱状，并与基板中的间充质密度增加有关。使用 5BrdU，在覆盖上颌骨和下颌骨的口腔和表皮细胞中观察到强烈的细胞增殖，这可能是受到上颌骨和下颌骨延续的潜在间充质的刺激。这些基板的扩张和融合产生角质喙。β 连环蛋白，主要是交界性的，但在喙上皮生发层的细胞核中也很少检测到，使分化的角质形成细胞保持团结，形成分层的角质上皮。这最初由一些大细胞层组成，这些细胞积累中间丝角蛋白 (IFK)，并产生角化的胚胎表皮，注定会在孵化周围脱落。以下角质细胞积累 IFK，但主要是 I/II 型角质β蛋白 (CBP) 并形成角质喙。这些 CBP 出现在喙中的强度低于壳中，但是使用针对 CBP 的通用抗体获得的更高强度表明其他 CBP 有助于喙角质材料的组成和刚度。