Craniosynostosis severity varies in patients with identical genetic mutations. To understand causes of this phenotypic variation, we backcrossed the FGFR2^+/C342Y mouse model of Crouzon syndrome onto congenic C57BL/6 and BALB/c backgrounds. Coronal suture fusion was observed in C57BL/6 (88% incidence, p < .001 between genotypes) but not in BALB/c FGFR2^+/C342Y mutant mice at 3 weeks after birth, establishing that that the two models differ in phenotype severity. To begin identifying pre-existing modifiers of craniosynostosis severity, we compared transcriptome signatures of cranial tissues from C57BL/6 vs. BALB/c FGFR2^+/+ mice. We separately analyzed frontal bone with coronal suture tissue from parietal bone with sagittal suture tissues because the coronal suture but not the sagittal suture fuses in FGFR2^+/C342Y mice. The craniosynostosis associated Twist and En1 transcription factors were down-regulated, while Runx2 was up-regulated, in C57BL/6 compared to BALB/c tissues, which could predispose to craniosynostosis. Transcriptome analyses under the GO term MAPK cascade revealed that genes associated with calcium ion channels, angiogenesis, protein quality control and cell stress response were central to transcriptome differences associated with genetic background. FGFR2 and HSPA2 protein levels plus ERK1/2 activity were higher in cells isolated from C57BL/6 than BALB/c cranial tissues. Notably, the HSPA2 protein chaperone is central to craniofacial genetic epistasis, and we find that FGFR2 protein is abnormally processed in primary cells from FGFR2^+/C342Y but not FGFR2^+/+ mice. Therefore, we propose that differences in protein quality control responses may contribute to genetic background influences on craniosynostosis phenotype severity.

具有相同基因突变的患者的颅缝早闭严重程度各不相同。为了了解这种表型变异的原因，我们将Crouzon 综合征的 FGFR2 ^+/C342Y小鼠模型回交到同类 C57BL/6 和 BALB/c 背景上。在 C57BL/6 中观察到冠状缝融合（88% 的发生率，基因型之间的 p < .001），但在出生后 3 周的BALB/c FGFR2 ^+/C342Y突变小鼠中没有观察到，这表明这两种模型在表型严重性方面存在差异。为了开始识别颅缝早闭严重程度的预先存在的调节剂，我们比较了 C57BL/6 与 BALB/c FGFR2 ^+/+颅骨组织的转录组特征老鼠。我们分别分析了带有冠状缝合组织的额骨和带有矢状缝合组织的顶骨，因为在 FGFR2 ^+/C342Y小鼠中，冠状缝合融合而不是矢状缝合融合。颅缝早闭相关的Twist和En1转录因子被下调，而Runx2与 BALB/c 组织相比，在 C57BL/6 中表达上调，这可能导致颅缝早闭。GO 术语 MAPK 级联下的转录组分析表明，与钙离子通道、血管生成、蛋白质质量控​​制和细胞应激反应相关的基因是与遗传背景相关的转录组差异的核心。从 C57BL/6 分离的细胞中 FGFR2 和 HSPA2 蛋白水平加上 ERK1/2 活性高于 BALB/c 颅组织。值得注意的是，HSPA2 蛋白伴侣是颅面遗传上位性的核心，我们发现 FGFR2 蛋白在 FGFR2 ^{+/C342Y 的}原代细胞中异常加工，但 FGFR2 ^{+/+ 没有}老鼠。因此，我们提出蛋白质质量控​​制反应的差异可能有助于遗传背景对颅缝早闭表型严重程度的影响。