Jain, V. D. | bioRxiv Science

bioRxiv2026

EFN-4/Ephrin converges with SAX-3/Robo, UNC-6/Netrin, and Heparan Sulfate Proteoglycan signaling to control MAB-5/Hox-dependent posterior Q neuroblast migration in Caenorhabditis elegans

Hox genes have been broadly implicated in nervous system development, but the molecular and genetic mechanisms that act downstream of Hox factors remain to be identified. The MAB-5 antennapedia-like Hox transcription factor is both necessary and sufficient to cause posterior migration of the Q neuroblast descendants in Caenorhabditis elegans. In response to MAB-5, the left-side QL descendants QL.a and QL.ap undergo a three-stage migration process, with each stage characterized by a posterior lamellipodial protrusion followed by cell body migration. The QL.ap cell differentiates into the PQR neuron posterior to the anus. Previous studies showed that the MAB-5-regulated gene efn-4/Ephrin was required for the third and final stage of QL.ap migration, with efn-4 mutation resulting in placement of PQR immediately anterior to the anus. This subtle and previously-undescribed phenotype opens the possibility that other known neuronal development genes could be involved. In this work, we screened known signaling mutants for third-stage PQR migration defects. We found that mutations in SAX-3/Robo signaling, UNC-6/Netrin signaling, and heparan sulfate proteoglycans (HSPGs) all displayed third-stage PQR migration defects. The effects in single mutants were weak compared to efn-4, and double mutant analysis revealed lack of genetic synergy, consistent with all of these molecules converging on a common pathway. This genetic analysis is consistent with physical interaction studies in vitro from another group that suggest that these molecules form connected communities of interacting extracellular domains, raising the possibility that they are all components of a large extracellular signaling complex required for posterior QL.ap migration. In this model, we envision that MAB-5/Hox drives EFN-4/Ephrin expression in QL.ap, which then seeds the formation of an extracellular signaling complex containing SAX-3/Robo signaling, UNC-6/Netrin signaling, and HSPGs that drives posterior lamellipodial formation and posterior migration.

developmental biology↗

bioRxiv2025

VAB-8/KIF26, LIN-17/Frizzled, and EFN-4/Ephrin, control distinct stages of posterior neuroblast migration downstream of the MAB-5/Hox transcription factor in Caenorhabditis elegans

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 target genes in QL lineage posterior migration are delineated, vab-8/KIF26, lin-17/Fz, and efn-4/Ephrin. First, 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; after QL.a division, posterior migration of QL.ap to a region immediately anterior to the anus; and final migration of QL.ap posterior to the anus to the final position where it differentiates into the PQR neuron. 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 target 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 trafficks distinct molecules to the plasma membrane that mediate distinct stages of migration, including LIN-17/Fz and EFN-4. Surpisingly, 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 works delineates a transcriptional program downstream of mab-5/Hox that controls posterior neuroblast migration, in response to Wnt signaling.

developmental biology↗