Nucleoporins are the constituents of nuclear pore complexes (NPCs) and are essential regulators of nucleocytoplasmic transport, gene expression and genome stability. The nucleoporin MEL-28/ELYS plays a critical role in post-mitotic NPC reassembly through recruitment of the NUP107-160 subcomplex and is required for correct segregation of mitotic chromosomes. MEL-28 has a dynamic behavior: it localizes to nuclear pore complexes and chromatin during interphase and shuttles to kinetochores during cell division. However, it is unknown how MEL-28 localization and activity is regulated.
Here we present a systematic functional and structural analysis of MEL-28 in C. elegans early development and human ELYS in cultured cells. We have identified functional domains responsible for NPC and kinetochore localization, chromatin binding, mitotic spindle matrix association and chromosome segregation. Surprisingly, we found that perturbations to MEL-28’s conserved AT-hook domain do not affect MEL-28 localization although they disrupt MEL-28 function and delay cell cycle progression in a DNA damage checkpoint-dependent manner. Our analyses also uncover a novel meiotic role of MEL-28. Together, these results show that MEL-28 has conserved structural domains that are essential for its fundamental roles in NPC assembly and chromosome segregation during meiosis and mitosis.
To understand the function of MEL-28 chromatin binding we have used DamID to identify the chromatin regions with which MEL-28 associates. Interestingly, MEL-28 is enriched at transcribed genes and correlates positively with active histone marks, suggesting that it may be involved in regulation of gene expression. We compared the MEL-28 chromatin profile with the profile of another nucleoporin, NPP-22, which is permanently anchored to the nuclear pore complex. Surprisingly, we found that the chromatin association profile of NPP-22 was more similar to the profile of the nuclear lamina protein LMN-1 than to MEL-28’s profile, suggesting that individual NPPs interact with specific chromatin domains. Finally, GO-term analysis reveals that MEL-28-associated genes are related to larval and reproductive development. This suggests that MEL-28 has postembryonic functions that have not yet been studied.