Most eukaryotes harbor two distinct pre-mRNA splicing machineries: the major spliceosome, which removes >99% of introns, and the minor spliceosome, which removes rare, evolutionarily conserved introns 1 – 4 . Although hypothesized to serve important regulatory functions 5 , physiologic roles for the minor spliceosome are not well understood. For example, the minor spliceosome component ZRSR2 is subject to recurrent, leukemia-associated mutations 6 – 9 , yet functional connections between minor introns, hematopoiesis, and cancers are unclear. Here, we identify that impaired minor intron excision via ZRSR2 loss enhances hematopoietic stem cell self-renewal. CRISPR screens mimicking nonsense-mediated decay of minor intron-containing mRNAs converged on LZTR1, a regulator of Ras-related GTPases 10 – 12 . LZTR1 minor intron retention was also discovered in the RASopathy Noonan syndrome, due to intronic mutations disrupting splicing, and diverse solid tumors. These data uncover minor intron recognition as a regulator of hematopoiesis, noncoding mutations within minor introns as potential cancer drivers, and links between ZRSR2 mutations, LZTR1 regulation, and leukemias.

Posttranscriptional machinery regulates inflammation and is associated with autoimmunity as well as tumorigenesis in collaboration with transcription factors. We previously identified the tumor suppressor gene transformed follicular lymphoma (TFL) on 6q25 in a patient with follicular lymphoma, which transformed into diffuse large B cell lymphoma. TFL families have a common RNase domain that governs macrophage-mediated inflammation. In human peripheral blood, TFL is dominantly expressed at the glycine- and tryptophan-rich cytoplasmic processing bodies of T lymphocytes, and it is persistently upregulated in activated T cells. To address its physiological role, we established TFL−/− mice in which TFL−/− lymphocytes proliferated more rapidly than TFL+/+ upon stimulation with inappropriate cytokine secretion, including IL-2, IL-6, and IL-10. Moreover, TFL inhibited the synthesis of cytokines such as IL-2, IL-6, IL-10, TNF-α, and IL-17a by 3′ untranslated region RNA degradation. Experimental autoimmune encephalitis induced in TFL−/− mice demonstrated persistent severe paralysis. CNS-infiltrated CD4+ T cells in TFL−/− mice contained a higher proportion of Th17 cells than did those in TFL+/+ mice during the resolution phase, and IL-17a mRNA levels were markedly increased in TFL−/− cells. These results suggest that TFL may play an important role in attenuating local inflammation by suppressing the infiltration of Th17 cells in the CNS during the resolution phase of experimental autoimmune encephalitis. TFL is a novel gradual and persistent posttranscriptional regulator, and the TFL-driven attenuation of excessive inflammation could contribute to recovery from T cell–mediated autoimmune diseases.

Granulocyte colony-stimulating factor (G-CSF) is widely used for peripheral blood stem/progenitor mobilization. G-CSF causes low-grade fever that is ameliorated by nonsteroidal anti-inflammatory drugs (NSAIDs), suggesting the activation of arachidonic acid (AA) cascade. How G-CSF regulated this reaction was assessed. G-CSF treatment in mice resulted in fever, which was canceled in prostaglandin E synthase (mPGES-1)-deficient mice. Mobilization efficiency was twice as high in chimeric mice lacking mPGES-1, specifically in hematopoietic cells, suggesting that prostaglandin E (PGE) from hematopoietic cells modulated the bone marrow (BM) microenvironment. Neutrophils from steady-state BM constitutively expressed mPGES-1 and significantly enhanced PGE production in vitro by β-adrenergic stimulation, but not by G-CSF, which was inhibited by an NSAID. Although neutrophils expressed all β-adrenergic receptors, only β3-agonist induced this phenomenon. Liquid chromatography-tandem mass spectrometry traced β-agonist-induced PGE synthesis from exogenous deuterium-labeled AA. Spontaneous PGE production was highly efficient in Gr-1 neutrophils among BM cells from G-CSF-treated mice. In addition to these in vitro data, the in vivo depletion of Gr-1 neutrophils disrupted G-CSF-induced fever. Furthermore, sympathetic denervation eliminated both neutrophil priming for PGE production and fever during G-CSF treatment. Thus, sympathetic tone-primed BM neutrophils were identified as one of the major PGE producers. PGE upregulated osteopontin, specifically in preosteoblasts, to retain progenitors in the BM via EP4 receptor. Thus, the sympathetic nervous system regulated neutrophils as an indispensable PGE source to modulate BM microenvironment and body temperature. This study provided a novel mechanistic insight into the communication of the nervous system, BM niche components, and hematopoietic cells.

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