The avian basilar papilla is a valuable model system for exploring the developmental determination and differentiation of sensory hair cells and their innervation. In the mature basilar papilla, hair cells form a well-known continuum between two extreme types—tall and short hair cells—that differ strikingly in their innervation. Previous work identified Wnt9a as a crucial factor in this differentiation. Here, we quantified the number and volume of immunolabelled presynaptic ribbons in tall and short hair cells of chickens, from developmental stages shortly after ribbons first appear to the mature posthatching condition. Two longitudinal locations were sampled, responding to best frequencies of approximately 1 kHz and approximately 5.5 kHz when mature. We found significant reductions of ribbon number during normal development in the tall-hair-cell domains, but stable, low numbers in the short-hair-cell domains. Exposing developing hair cells to continuous, excessive Wnt9a levels (through virus-mediated overexpression) led to transiently abnormal high numbers of ribbons and a delayed reduction of ribbon numbers at all sampled locations. Thus, (normally) short-hair-cell domains also showed tall-hair-cell like behaviour, confirming previous findings (Munnamalai et al., 2017). However, at 3 weeks posthatching, ribbon numbers had decreased to the location-specific typical values of control hair cells at all sampled locations. Furthermore, as shown previously, mature hair cells at the basal, high-frequency location harboured larger ribbons than more apically located hair cells. This was true for both normal and Wnt9a-overexposed basilar papillae.

中文翻译：

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鸡基底-乳头毛细胞突触前带数的发育成熟及其长期过表达Wnt9a的扰动

鸟类基底乳头是探索感觉毛细胞的发育决定和分化及其神经支配的有价值的模型系统。在成熟的基底乳头中，毛细胞在两种极端类型（高毛细胞和短毛细胞）之间形成了众所周知的连续体，它们的神经支配明显不同。以前的工作将 Wnt9a 确定为这种分化的关键因素。在这里，我们量化了鸡的高毛和短毛细胞中免疫标记的突触前丝带的数量和体积，从丝带首次出现后不久的发育阶段到成熟的孵化后条件。对两个纵向位置进行采样，对大约 1 kHz 的最佳频率和成熟时大约 5.5 kHz 的最佳频率作出响应。我们发现，在高毛细胞域的正常发育过程中，色带数量显着减少，但在短毛细胞域中，丝带数量稳定且低。将发育中的毛细胞暴露于连续的、过度的 Wnt9a 水平（通过病毒介导的过度表达）导致短暂异常的大量丝带和所有采样位置的丝带数量延迟减少。因此，（通常）短毛细胞结构域也表现出高毛细胞样行为，证实了先前的发现（Munnamalai 等，2017）。然而，在孵化后 3 周，带状数量已减少到所有采样位置的对照毛细胞的特定位置的典型值。此外，如前所述，在基部、高频位置的成熟毛细胞比位于更顶端的毛细胞具有更大的丝带。