The sequence of pEL1174 (Pegl-17::efn-4cDNA).

Hox transcription factors are involved in neuronal and neural crest development and differentiation, including migration, but the genetic programs employed by Hox genes to regulate terminal differentiation remain to be defined. In C. elegans, the Antennapedia-like Hox factor MAB-5 is both necessary and sufficient to induce posterior migration of the Q lineage neuroblasts and neurons downstream of canonical Wnt signaling. Q lineage fluorescence-activated cell sorting and RNA seq in mab-5 loss-of-function and gain-of-function backgrounds revealed genes with expression in the Q lineage dependent upon MAB-5. Here, the roles of three mab-5-regulated genes in QL lineage posterior migration are delineated, vab-8/KIF26, lin-17/Fz, and efn-4/Ephrin. Live, time-lapse imaging of QL.a and QL.ap posterior migration revealed that this migration occurs in three distinct stages: QL.a migration posterior to QL.p (1st stage); after QL.a division, posterior migration of QL.ap to a region immediately anterior to the anus (2nd stage); and final migration of QL.ap posterior to the final position where it differentiates into the PQR neuron (3rd stage). vab-8 affected each of the three stages, lin-17 affected stages two and three, and efn-4 was required for the third stage of posterior QL.ap migration. Thus, different MAB-5-regulated genes control distinct stages of posterior migration. mab-20/Semaphorin, a known interaction partner with efn-4, also affected only the third stage similar to efn-4. Suppression of mab-5 gof posterior migration confirmed that these genes act downstream of mab-5 in posterior migration. Possibly, VAB-8/KIF26 helps deliver distinct molecules to the plasma membrane that mediate distinct stages of migration, including LIN-17/Fz and EFN-4. Surprisingly, failure of stages two and three led to the premature extension of a posterior dendritic protrusion, which normally forms after QL.ap had migrated to its final position and PQR differentiation begins. This suggests a link between migration and differentiation, where differentiation is delayed while migration proceeds. In sum, this work delineates a transcriptional program downstream of mab-5/Hox that controls posterior neuroblast migration, in response to Wnt signaling.Hox转录因子（Hox transcription factors）参与神经元与神经嵴的发育及分化过程，涵盖细胞迁移环节，但Hox基因调控终末分化所依托的遗传程序仍有待明确。在秀丽隐杆线虫（C. elegans）中，类似触角足的Hox因子MAB-5在经典Wnt信号通路（canonical Wnt signaling）下游，既可诱导Q谱系成神经细胞及其子代神经元的后部迁移，且该调控功能既是必需的，也是充分的。研究人员对MAB-5功能丧失与功能获得背景下的Q谱系开展荧光激活细胞分选（fluorescence-activated cell sorting）与RNA测序（RNA seq），鉴定出了Q谱系中表达依赖于MAB-5的基因。 本研究明确了三个受MAB-5调控的基因在QL谱系后部迁移中的作用，分别为vab-8/KIF26、lin-17/Fz以及efn-4/Ephrin。通过对QL.a与QL.ap后部迁移进行活体细胞延时成像（live time-lapse imaging），发现该迁移过程可分为三个截然不同的阶段：第一阶段为QL.a向QL.p后方迁移；第二阶段为QL.a分裂完成后，QL.ap向紧临肛门前方的区域迁移；第三阶段为QL.ap最终迁移至其分化为PQR神经元的最终位置。 实验结果显示：vab-8可影响上述三个迁移阶段，lin-17影响第二与第三阶段，而efn-4仅为QL.ap后部迁移的第三阶段所必需。由此可见，不同的MAB-5调控基因分别控制后部迁移的不同阶段。已知与efn-4存在相互作用的伙伴mab-20/信号素（Semaphorin），同样仅影响第三阶段，其表型与efn-4一致。对MAB-5功能获得型突变体的后部迁移进行抑制实验证实，这些基因均作用于MAB-5下游参与后部迁移过程。 推测显示，VAB-8/KIF26可能负责将介导不同迁移阶段的特定分子（如LIN-17/Fz与EFN-4）运送至质膜。令人意外的是，第二、第三阶段迁移受阻会导致后部树突突起过早伸出——而该突起通常在QL.ap迁移至最终位置并开始分化为PQR神经元后才会形成。这表明迁移与分化之间存在关联：当迁移过程仍在进行时，分化进程会被延迟。 综上，本研究明确了受Wnt信号调控的、位于MAB-5/Hox下游的转录程序，该程序可控制成神经细胞的后部迁移。