During gastrulation, Hox genes are activated in a time-sequence that follows the order of the genes along their clusters. This property, which is observed in all animals that develop following a progressive rostral-to-caudal morphogenesis, is associated with changes in the chromatin structure and epigenetic profiles of Hox clusters, suggesting a process at least partly based on sequential gene accessibility. Here, we discuss recent work on this issue, as well as a possible mechanism based on the surprising conservation in both the distribution and orientation of CTCF sites inside vertebrate Hox clusters.

中文翻译：

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Hox 计时器基于 CTCF 相关机制：与分段身体计划的关系

在原肠胚形成过程中，Hox 基因按照基因簇中基因的顺序被激活。这种特性在所有从头端到尾端形态发生进行性发育的动物中都观察到，它与染色质结构和 Hox 簇的表观遗传谱的变化有关，表明这一过程至少部分基于顺序基因可及性。在这里，我们讨论了最近在这个问题上的工作，以及基于脊椎动物 Hox 簇内 CTCF 位点的分布和方向的惊人保守性的可能机制。