Department of Molecular Reproduction, Development and Genetics, Biological Sciences Division, Indian Institute of Science, Bangalore 560012, India.
Department of Mathematics, Western Washington University, Bellingham, WA 98229, USA.
Mech Dev. 2019 Apr;156:41-54. doi: 10.1016/j.mod.2019.03.001. Epub 2019 Mar 10.
The tetrapod appendicular skeleton is initiated as spatially patterned mesenchymal condensations. The size and spacing of these condensations in avian limb buds are mediated by a reaction-diffusion-adhesion network consisting of galectins Gal-1A, Gal-8 and their cell surface receptors. In cell cultures, the appearance of condensations is synchronized across distances greater than the characteristic wavelength of their spatial pattern. We explored the possible role of observed oscillations of the transcriptional co-regulator Hes1 in this phenomenon. Treatment of micromass cultures with DAPT, a γ-secretase inhibitor, damped Hes1 oscillations, elevated Gal-1A and -8 mRNA levels, and led to irregularly-sized proto-condensations that subsequently fused. In developing limb buds, DAPT led to spatially non-uniform Hes1 expression and fused, truncated and misshapen digits. Periodicity in adhesive response to Gal-1A, a plausible Hes1-dependent function, was added to a previously tested mathematical model for condensation patterning by the two-galectin network. The enhanced model predicted regularization of patterning due to synchronization of Hes1 oscillations and resulting spatiotemporal coordination of its expression. The model also predicted changes in galectin expression and patterning in response to suppression of Hes1 expression, which were confirmed in in vitro experiments. Our results indicate that the two-galectin patterning network is regulated by Hes1 dynamics, the synchronization of which refines and regularizes limb skeletogenesis.
四足动物附肢骨骼是作为空间模式化的间充质凝聚物而启动的。这些凝聚物在禽类肢体芽中的大小和间距由一个由半乳糖凝集素 Gal-1A、Gal-8 及其细胞表面受体组成的反应-扩散-黏附网络介导。在细胞培养物中，凝聚物的出现会在距离上同步，其距离大于其空间模式的特征波长。我们探索了观察到的转录共调节因子 Hes1 振荡在这种现象中的可能作用。用 γ-分泌酶抑制剂 DAPT 处理微团培养物，会抑制 Hes1 振荡，提高 Gal-1A 和 Gal-8 mRNA 水平，并导致不规则大小的原凝聚物融合。在发育中的肢体芽中，DAPT 导致 Hes1 表达的空间不均匀，并导致融合、截断和畸形的指骨。对半乳糖凝集素 Gal-1A 的黏附反应的周期性，这是一个可能依赖 Hes1 的功能，被添加到之前测试的由双半乳糖凝集素网络进行凝聚物模式形成的数学模型中。增强后的模型预测由于 Hes1 振荡的同步及其表达的时空协调，模式形成会得到规则化。该模型还预测了抑制 Hes1 表达后半乳糖凝集素表达和模式形成的变化，这在体外实验中得到了证实。我们的结果表明，双半乳糖凝集素模式形成网络受 Hes1 动力学的调节，其同步可以细化和规则化肢体骨骼发生。
