Department Prosektur Anatomie, Westfälische Wilhelms-University, Münster, Germany.
J Anat. 2019 Apr;234(4):551-563. doi: 10.1111/joa.12945. Epub 2019 Feb 7.
In the posterior placodal area (PPA) of C57BL/6N mice and primate-related Tupaia belangeri (Scandentia), apoptosis helps to establish morphologically separated otic and epibranchial placodes. Here, we demonstrate that basically identical patterns of apoptosis pass rostrocaudally through the Pax2 PPA of chicken embryos. Interplacodal apoptosis eliminates unneeded cells either between the otic anlage and the epibranchial placodes 1, 2 and/or 3, respectively (type A), or between neighbouring epibranchial placodes (type B). These observations support the idea that in chicken embryos, as in mammals, interplacodal apoptosis serves to remove vestigial lateral line placodes (Washausen & Knabe, 2018, Biol Open 7, bio031815). A special case represents the recently discovered Pax2 /Sox2 paratympanic organ (PTO) placode that has been postulated to be molecularly distinct from and developmentally independent of the ventrally adjacent first epibranchial (or 'geniculate') placode (O'Neill et al. 2012, Nat Commun 3, 1041). We show that Sox2 (PTO placodal) cells seem to segregate from the Pax2 geniculate placode, and that absence of Pax2 in the mature PTO placode is due to secondary loss. We further report that, between Hamburger-Hamilton (HH) stages HH14 and HH26, apoptosis in the combined anlage of the first epibranchial and PTO placodes is almost exclusively found within and/or immediately adjacent to the dorsally located PTO placode. Hence, apoptosis appears to support decision-making processes among precursor cells of the early developing PTO placode and, later, regression of the epibranchial placodes 2 and 3.
在 C57BL/6N 小鼠和与灵长类动物相关的树鼩（攀鼩目）的后脑基板区（PPA）中，细胞凋亡有助于建立形态上分离的耳原基和前鳃基板。在这里，我们证明，在鸡胚的 Pax2 PPA 中，细胞凋亡基本上以相同的模式从前向后穿过。基板间凋亡消除了耳原基和前鳃基板 1、2 和/或 3 之间的多余细胞（A 型），或者消除了相邻的前鳃基板之间的多余细胞（B 型）。这些观察结果支持这样一种观点，即在鸡胚中，与哺乳动物一样，基板间凋亡有助于去除退化的侧线基板（Washausen 和 Knabe，2018，Biol Open 7，bio031815）。一个特殊的情况是最近发现的 Pax2/Sox2 副听器官（PTO）基板，该基板被假定在分子上与腹侧相邻的第一个前鳃（或'神经节'）基板不同，并且在发育上独立（O'Neill 等人，2012，Nat Commun 3，1041）。我们表明 Sox2（PTO 基板）细胞似乎与 Pax2 神经节基板分离，并且成熟的 PTO 基板中 Pax2 的缺失是由于继发性缺失。我们进一步报告说，在 Hamburger-Hamilton（HH）阶段 HH14 和 HH26 之间，第一前鳃和 PTO 基板的联合基板中的凋亡几乎完全局限于或紧邻位于背部的 PTO 基板内。因此，凋亡似乎支持早期发育的 PTO 基板前体细胞中的决策过程，以及后来的 2 号和 3 号前鳃基板的退化。
