Differential roles of miR‐15a/16‐1 and miR‐497/195 clusters in immune cell development and homeostasis

Abstract

MicroRNAs (miRNAs) post-transcriptionally repress almost all genes in mammals and thereby form an additional layer of gene regulation. As such, miRNAs impact on nearly every physiological process and have also been associated with cancer. Prominent examples of such miRNAs can be found in the miR-15 family, composed of the bicistronic clusters miR-15a/ 16-1, miR-15b/16-2, and miR-497/195. In particular, the miR-15a/16-1 cluster is deleted in almost two thirds of all chronic B lymphocytic leukemia (CLL) cases, a phenotype that is also recapitulated by miR-15a/16-1deficient as well as miR-15b/16-2-deficient mice. Under physiological conditions, those two clusters have been implicated in T-cell function, and B-cell and natural killer (NK) cell development; however, it is unclear whether miR-497 and miR-195 confer similar roles in health and disease. Here, we have generated a conditional mouse model for tissue-specific deletion of miR-497 and miR-195. While mice lacking miR-15a/16-1 in the hematopoietic compartment developed clear signs of CLL over time, aging mice deficient for miR-497/195 did not show such a phenotype. Likewise, loss of miR-15a/16-1 impaired NK and early B-cell development, whereas miR-497/195 was dispensable for these processes. In fact, a detailed analysis of miR-497/195-deficient mice did not reveal any effect on steady-state hematopoiesis or immune cell function. Unexpectedly, even whole-body deletion of the cluster was well-tolerated and had no obvious impact on embryonic development or healthy life span. Therefore, we postulate that the miR-497/195 cluster is redundant to its paralog clusters or that its functional relevance is restricted to certain physiological and pathological conditions.

Regulatory noncoding RNAs: functions and applications in health and disease

“…For instance, Xu et al [1] show that microRNA-520c-3p functions as a novel tumor suppressor in lung adenocarcinoma, and Sun et al [2] propose that microRNA-134 inhibits osteosarcoma angiogenesis and proliferation. Very recent developments have also shown that microRNA clusters can have differential roles in development and homeostasis, as reported by Herzog et al Their conditional and whole-body mouse model deletion of miR-497/195, part of the miR-15 family, did not show onsets of chronic B lymphocytic leukemia or impaired immune cell development, in contrast to mice lacking their miR-15 paralogs [3].…”

“…Very recent developments have also shown that microRNA clusters can have differential roles in development and homeostasis, as reported by Herzog et al . Their conditional and whole‐body mouse model deletion of miR‐497/195, part of the miR‐15 family, did not show onsets of chronic B lymphocytic leukemia or impaired immune cell development, in contrast to mice lacking their miR‐15 paralogs [3].…”

The miR-15a/16-1 and miR-15b/16-2 clusters regulate early B cell development by limiting IL-7 receptor expression

“…To study whether a complete loss of the miR-15 family members expressed in the hematopoietic compartment would affect physiologic immune cell development and function we generated a conditional miR-15a/16-1 miR-15b/16-2 knockout mouse model. We decided to neglect the miR-497/195 cluster in this setting, as it is only marginally expressed in immune cells and was found to be dispensable for the immune system in our previously described miR-497/195 knockout mouse model (Hutter et al 2020). The conditional miR-15a/16-1 and miR-15b/16-2 knockout alleles were generated using CRISPR/Cas9-assisted editing to flank the endogenous clusters with loxP sites in embryonic stem (ES) cells (Figs.…”

“…The conditional miR-15a/16-1 and miR-15b/16-2 alleles were generated by CRISPR/Cas9-facilitated homologous recombination in murine ES cells, as already described for targeting of the miR-497/195 cluster (Hutter et al 2020). In short, KH2 ES cells ( (Premsrirut et al 2011), C57BL/6 x 129S4/Sv/Jae background, kindly provided by J. Zuber, IMP, Vienna) were electroporated (Nucleofector Kit; Lonza, Switzerland) with two Cas9/sgRNA vectors encoding GFP as a marker and the targeting DNA template containing the miRNA cluster flanked by loxP sites.…”

“…Noteworthy, whole-body deletion of miR-15a/16-1 and miR-15b/16-2 in mice did not result in accelerated CLL onset but rather induced acute myeloid leukemia (AML) development, indicating that distinct cell types have a different sensitivity for a reduction of miR-15 levels (Lovat et al 2020). As the miR-497/195 cluster is only marginally expressed in immune cells, it is dispensable for immune cell development and function, while the other two clusters are highly expressed and several studies are beginning to elucidate their physiologic functions (Kuchen et al 2010; Hutter et al 2020). The miR-15a/16-1 cluster was shown to be important for natural killer (NK) cell development, as its NK cell-specific deletion partially blocked NK cell maturation in the spleen (Sullivan et al 2015).…”