Arresta Emiliano, Bernardini Sergio, Gargioli Cesare, Filoni Sergio, Cannata Stefano M
Dipartimento di Biologia, Università di Roma Tor Vergata, via della Ricerca Scientifica, I - 00133 Rome, Italy.
J Exp Zool A Comp Exp Biol. 2005 Jan 1;303(1):1-12. doi: 10.1002/jez.a.138.
In larval X. laevis the capacity to regenerate a lens under the influence of inductive factors present in the vitreous chamber is restricted to the outer cornea and pericorneal epidermis (Lentogenic Area, LA). However, in early embryos, the whole ectoderm is capable of responding to inductive factors of the larval eye forming lens cells. In a previous paper, Cannata et al. (2003) demonstrated that the persistence of lens-forming competence in the LA is the result of early signals causing lens-forming bias in the presumptive LA and of late signals from the eye causing cornea development. This paper analyzes 1) the decrease of the lens-forming capacity in ectodermal regions both near LA (head epidermis) and far from LA (flank epidermis) during development, 2) the capacity of the head epidermis and flank epidermis to respond to lens-competence promoting factors released by an eye transplanted below these epidermal regions, and 3) the eye components responsible for the promoting effect of the transplanted eye. Results were obtained by implanting fragments of ectoderm or epidermis into the vitreous chamber of host tadpoles and by evaluating the percentage of implants positive to a monoclonal antibody anti-lens. These results demonstrated that the lens-forming competence in the flank region is lost at the embryonic stage 30/31 and is weakly restored by eye transplantation; however, lens-forming competence in the head region is lost at the larval stage 48 and is strongly restored by eye transplantation. The authors hypothesize that during development the head ectoderm outside the LA is attained by low levels of the same signals that attain the LA and that these signals are responsible for the maintenance of lens-forming competence in the cornea and pericorneal epidermis of the larva. In this hypothesis, low levels of these signals slacken the decrease of the lens-forming competence in the head ectoderm and make the head epidermis much more responsive than the flank epidermis to the effect of promoting factors released by a transplanted eye. Results obtained after transplantation of eyes deprived of some components indicate that the lens and the retina are the main source of these promoting factors. The immunohistochemical detection of the FGFR-2 (bek variant) protein in the epidermis of stage 53 larvae submitted to eye transplantation at stage 46 showed that the eye transplantation increased the level of FGFR-2 protein in the head epidermis but not in the flank epidermis, indicating that the lens-forming competence in X. laevis epidermis could be related to the presence of an activated FGF receptor system in the responding tissue.
在非洲爪蟾幼体中，在玻璃体腔中存在的诱导因子影响下再生晶状体的能力仅限于外角膜和角膜周表皮（晶状体发生区，LA）。然而，在早期胚胎中，整个外胚层都能够对幼体眼的诱导因子作出反应而形成晶状体细胞。在之前的一篇论文中，卡纳塔等人（2003年）证明，LA中晶状体形成能力的持续存在是早期信号导致假定LA中形成晶状体偏向以及来自眼睛的晚期信号导致角膜发育的结果。本文分析了：1）发育过程中，LA附近（头部表皮）和远离LA（侧腹表皮）的外胚层区域中晶状体形成能力的下降；2）头部表皮和侧腹表皮对移植到这些表皮区域下方的眼睛释放的促进晶状体形成能力的因子作出反应的能力；3）负责移植眼促进作用的眼成分。通过将外胚层或表皮片段植入宿主蝌蚪的玻璃体腔，并评估对一种抗晶状体单克隆抗体呈阳性的植入物的百分比来获得结果。这些结果表明，侧腹区域的晶状体形成能力在胚胎期30/31时丧失，通过眼移植可微弱恢复；然而，头部区域的晶状体形成能力在幼体期48时丧失，通过眼移植可强烈恢复。作者推测，在发育过程中，LA外部的头部外胚层通过与到达LA的相同信号的低水平接触而获得这些信号，并且这些信号负责维持幼体角膜和角膜周表皮中的晶状体形成能力。在这一假说中，这些信号的低水平减缓了头部外胚层中晶状体形成能力的下降，并使头部表皮比侧腹表皮对移植眼释放的促进因子的作用更敏感。对在第46阶段接受眼移植的第53阶段幼体表皮中FGFR - 2（bek变体）蛋白的免疫组织化学检测表明，眼移植增加了头部表皮中FGFR - 2蛋白的水平，但未增加侧腹表皮中的水平，这表明非洲爪蟾表皮中的晶状体形成能力可能与反应组织中活化的FGF受体系统的存在有关。
