The Six1 transcription factor plays a major role in craniofacial development. Mutations in SIX1 and its co-factor, EYA1, are causative for about 50% of Branchio-otic/Branchio-oto-renal syndrome (BOR) patients, who are characterized by variable craniofacial, otic and renal malformations. We previously screened for other proteins that might interact with Six1 to identify additional genes that may play a role in BOR, and herein characterize the developmental role of one of them, Microspherule protein 1 (Mcrs1). We found that in cultured cells, Mcrs1 bound to Six1 and in both cultured cells and embryonic ectoderm reduced Six1-Eya1 transcriptional activation. Knock-down of Mcrs1 in embryos caused an expansion of the domains of neural plate genes and two genes expressed in both the neural plate and neural crest (zic1, zic2). In contrast, two other genes expressed in pre-migratory neural crest (foxd3, sox9) were primarily reduced. Cranial placode genes showed a mixture of expanded and diminished expression domains. At larval stages, loss of Mcrs1 resulted in a significant reduction of otic vesicle gene expression concomitant with a smaller otic vesicle volume. Experimentally increasing Mcrs1 above endogenous levels favored the expansion of neural border and neural crest gene domains over cranial placode genes; it also reduced otic vesicle gene expression but not otic vesicle volume. Co-expression of Mcrs1 and Six1 as well as double knock-down and rescue experiments establish a functional interaction between Mcrs1 and Six1 in the embryo, and demonstrate that this interaction has an important role in the development of craniofacial tissues including the otic vesicle.

Six1转录因子在颅面发育中起主要作用。SIX1及其辅助因子EYA1中的突变引起约50％的分支性/支气管-肾-肾综合征（BOR）患者的病因，这些患者的特征是颅面，耳和肾畸形多种多样。我们先前筛选了可能与Six1相互作用的其他蛋白质，以鉴定可能在BOR中起作用的其他基因，并在此表征了其中之一微球蛋白1（Mcrs1）的发育作用。我们发现，在培养的细胞中，Mcrs1与Six1结合，在培养的细胞和胚胎外胚层中均减少了Six1-Eya1转录激活。胚胎中Mcrs1的敲低导致神经板基因和两个在神经板和神经c（zic1，zic2）中表达的基因的域扩展。相反，另外两个基因在迁移前的神经neural中表达（foxd3，sox9）主要减少。颅骨斑基因显示了扩展和缩小的表达域的混合物。在幼虫阶段，Mcrs1的丧失导致耳囊基因表达显着减少，而耳囊体积更小。实验性地将Mcrs1增加到内源水平之上，比颅底基因更倾向于扩大神经边界和神经c基因域。它也减少了耳泡基因表达，但不减少耳泡体积。Mcrs1和Six1的共表达以及双重敲低和挽救实验在胚胎中建立了Mcrs1和Six1之间的功能相互作用，并证明这种相互作用在颅面组织（包括耳囊）的发育中具有重要作用。