## 4 Discussion  
We identified enhancer RNAs (eRNAs) that are enriched in erythroid cells and have long-range interactions by integrating multi-omics approaches. However, we found that the majority of these eRNAs do not form chromatin loops with erythroid genes. This suggests that if these eRNAs play a role in erythropoiesis, they likely act indirectly or function in trans to regulate erythroid genes without being mediated by chromatin looping. Among these erythroid long-range interacting eRNAs, we studied one specific eRNA, _CpoxreRNA_. The knockdown of _CpoxreRNA_ by shRNA results in impaired cell proliferation and enucleation during terminal erythropoiesis. Interestingly, in earlier work, we observed that the knockdown of mRNA for the neighboring coding gene _Cpox_ had no effect on erythropoiesis [71; 72]. Additionally, _CpoxreRNA_ plays an architectural role in mediating chromatin looping between its genomic locus and TAD boundaries, as these interactions are reduced upon _CpoxreRNA_ loss (Supplementary Figure S5D). We observed different phenotypes for shRNA KD or KO of _CpoxreRNA_, which inhibit erythropoiesis, compared to KD or KO of _Cpox_, which do not affect erythropoiesis [71]. The latter result is consistent with _Cpox_ being dispensable for erythropoiesis [72]. However, _CpoxreRNA_ seems important for erythroid cell maturation. We observed impaired proliferation and enucleation after the loss of _CpoxreRNA_. This may be due to other erythroid genes that were dysregulated in the _CpoxreRNA_ KD or KO cells, thus affecting terminal erythropoiesis. Indeed, we found that some erythroid gene loci were bound by _CpoxreRNA_ via ChIP-seq experiments, and their expression was reduced upon _CpoxreRNA_ loss (Figure 5). Active enhancers can produce non-coding RNAs, which are often transcribed bidirectionally and have short half-lives due to rapid degradation by the RNA exosome after transcription [3; 4; 5; 34; 70]. Studies have reported that some eRNAs play regulatory roles and can activate target promoters that their genomic loci make contact with, acting as RNA activators (RNAa) [9; 26; 27]. Other studies have reported trans-acting eRNAs that regulate genes located distally on the same chromosome or on different chromosomes, such as Blood-linc [29], DRReRNA [23], GATA2 AS [30], and HOXDeRNA [22]. These types of trans-acting eRNAs are often polyadenlated, allowing them to be protected from degradation upon transcription and potentially enabling them to diffuse within the nucleus [34; 70]. We found that _CpoxreRNA_ is also polyadenlated, consistent with its proposed trans-acting properties. Cohesin has been shown to interact with eRNAs, such as DRReRNA, which recruits cohesin to the target gene locus [23; 31]. Using the non-repetitive 5\({}^{\prime}\) region of _CpoxreRNA_ as bait, we found that it can interact with the CTCF/cohesin complex. The remaining 3\({}^{\prime}\) part of _CpoxreRNA_ contains several repetitive elements, including three ERVL family transposons, one of which is rodent-specific and appears to be intact (Supplementary Figure S1C). The role of the 3\({}^{\prime}\) parts of _CpoxreRNA_ in its function as an eRNA, and particularly in its mobility, remains unknown. Our examination of ChIP-seq data from ENCODE shows that the _CpoxreRNA_ target gene loci already have CTCF/cohesin binding in undifferentiated MEL cells (Supplementary Figure S3A), while the highest levels of _CpoxreRNA_ are found in differ entiated MEL cells. There is a CTCF/cohesin binding site in the _CpoxeRNA_ locus, which may serve as the source of CTCF/cohesin that binds to _CpoxeRNA_ upon its transcription. We did not find inter-chromosomal loops at the _CpoxeRNA_ genomic locus in the fetal liver Promoter Capture Hi-C data [52] or high-resolution cell cycle in situ Hi-C data from G1 ER cells [74]. Therefore, we propose that _CpoxeRNA_ may migrate in the nuclear environment via CTCF/cohesin complex interaction, allowing binding at target sites.