Roberson Whitney, Holland Jorden N, Riley Bruce B
Biology Department, Texas A&M University, College Station, TX, 77843-3258, USA.
Biology Department, Texas A&M University, College Station, TX, 77843-3258, USA.
Dev Biol. 2025 Jan;517:157-167. doi: 10.1016/j.ydbio.2024.09.009. Epub 2024 Sep 25.
During inner ear development, specification of sensory epithelia requires dynamic regulation of Fgf signaling. In zebrafish, high levels of Fgf are necessary and sufficient to specify the utricular/vestibular macula, whereas the saccular/auditory macula requires a discreet lower level of Fgf. Transcription factors Pax2a and Pax5 act downstream of Fgf to help specify utricular identity, loss of which leads to sporadic extrusion of hair cells from the utricular macula. The mechanism for utricular instability is not clear but is potentially related to reduced expression of cdh1/Ecad caused by disruption of pax2a. Here we find that utricular hair cells in pax2-/- and pax5-/- mutants gradually lose adhesive contact with the macula, leading to ejection of intact hair cells from either the basal or apical surface. The phenotype is far more severe in pax2a-/- mutants and is progressive, resulting in loss of large swaths of the utricular hair cells by 82 hpf. Instability is caused by elevated Fgf signaling in the utricle, as modest reduction of Fgf signaling with a low dose of SU5402 prevents hair cell loss in pax2a-/- mutants. Misexpression of cdh1/Ecad in pax2a-/- mutants partially rescues pax2a-/- mutants. Elevating β-catenin levels by treatment with BIO, or misexpression of a mutant form of β-catenin lacking transcriptional activity but retaining cell adhesion function, fully rescues pax2a-/- mutants. In contrast, Wnt signaling is not required for utricular stability. Thus, Pax2/5 factors serve to counteract the destabilizing effects of elevated Fgf signaling needed to specify utricular identity.
在内耳发育过程中,感觉上皮的特化需要Fgf信号的动态调节。在斑马鱼中,高水平的Fgf对于确定椭圆囊/前庭斑是必要且充分的,而球囊/听觉斑则需要适度较低水平的Fgf。转录因子Pax2a和Pax5在Fgf下游起作用,以帮助确定椭圆囊的身份,其缺失会导致椭圆囊斑中的毛细胞偶尔挤出。椭圆囊不稳定的机制尚不清楚,但可能与pax2a破坏导致的cdh1/Ecad表达降低有关。在这里,我们发现pax2-/-和pax5-/-突变体中的椭圆囊毛细胞逐渐失去与斑的粘附接触,导致完整的毛细胞从基底或顶端表面排出。该表型在pax2a-/-突变体中更为严重且呈进行性发展,到82 hpf时导致大片椭圆囊毛细胞丢失。不稳定性是由椭圆囊中Fgf信号升高引起的,因为用低剂量的SU5402适度降低Fgf信号可防止pax2a-/-突变体中的毛细胞丢失。在pax2a-/-突变体中过表达cdh1/Ecad可部分挽救pax2a-/-突变体。通过用BIO处理提高β-连环蛋白水平,或过表达缺乏转录活性但保留细胞粘附功能的β-连环蛋白突变体形式,可完全挽救pax2a-/-突变体。相比之下,Wnt信号对于椭圆囊的稳定性不是必需的。因此,Pax2/5因子起到抵消确定椭圆囊身份所需的Fgf信号升高的不稳定作用。