Actin remodeling driven by circLIMA1: sperm cell as an intriguing cellular model

Abstract

CircRNA cargo in spermatozoa (SPZ) participates in setting cell quality, in terms of morphology and motility. Cannabinoid receptor CB1 activity is correlated with a proper spermatogenesis and epididymal sperm maturation. Despite CB1 promotes endogenous skill to circularize mRNAs in SPZ, few notions are reported regarding the functional link between endocannabinoids and spermatic circRNA cargo. In CB1 knock-out male mice, we performed a complete dataset of spermatic circRNA content by microarray strategy. Differentially expressed (DE)-circRNAs, as a function of genotype, were identified. Within DE-circRNAs, we focused the attention on circLIMA1, as putative actin-cytoskeleton architecture regulator. The validation of circLIMA1 dependent-competitive endogenous RNA (ceRNA) network (ceRNET) in in vitro cell line confirmed its activity in the regulation of the cytoskeletal actin. Interestingly, a dynamic actin regulation in SPZ nuclei was found during their epididymal maturation. In this scenario, we showed for the first time an intriguing sperm nuclear actin remodeling, regulated via a ceRNET-independent pathway, consisting in the nuclear shuttling of circLIMA1-QKI interactome and downstream in Gelsolin regulation. In particular, the increased levels of circLIMA1 in CB1 knock-out SPZ, associated with an inefficient depolymerization of nuclear actin, specifically illustrate how endocannabinoids, by regulating circRNA cargo, may contribute to sperm morpho-cellular maturation.

A landscape of mouse mitochondrial small non-coding RNAs

“…contributes to proper spermatogenesis in terms of morphology and then motility [74]. Overall, those results support the idea that regulation via miRNAs could be functionally relevant for mitochondria biology, since a pool of miRNAs could be related to the basic function of mitochondria shared by different cell types, and others may be related to the specialized functions of each tissue.…”

“…The enrichment of biological pathways implied in different signaling routes was probably expected for miRNAs associated to mitochondria, since the central role of the organelle in metabolism and homeostasis and the results here reported highlight the potential strong miRNA contribution. Behind those pathways enriched for mitomiRs arising from all analyzed tissues, others are specifically found for tissue-specific mitomiRs; e.g, “insuline resistance” and “Type II diabetes mellitus” pathways were found for liver-specific mitomiRs; “Wnt signling pathway”, well-known to be related to gluconeogenesis, was found for WAT; “Regulation of actin cytoskeleton” pathway emerges significantly enriched for mitomiRs in testis, where actin remodeling contributes to proper spermatogenesis in terms of morphology and then motility [ 74 ]. Overall, those results support the idea that regulation via miRNAs could be functionally relevant for mitochondria biology, since a pool of miRNAs could be related to the basic function of mitochondria shared by different cell types, and others may be related to the specialized functions of each tissue.…”

Novel Insights into circRNA Saga Coming from Spermatozoa and Epididymis of HFD Mice

“…Previously, we identified FUS as the principal RBP able to orchestrate the endogenous formation of spermatic circRNA, and QKI as one of the favorite FUS molecular interactors needed for its RNA circulating skills [ 29 , 35 ]. Based on these pieces of evidence, we have morphologically and molecularly characterized FUS protein in both HFD sperm and epididymis in order to demonstrate its potential involvement in molecular mechanisms underlying both spermatic and epididymal circRNA biogenesis.…”

“…Considering that epididymal layered epithelium is dependent on cell-to-cell junctions and is able to coordinate protein-to-protein interactions to ensure several biological processes [ 59 , 60 , 61 , 62 , 63 , 64 ], we asked if an anomalous backsplicing mechanism, dependent on impaired FUS molecular partner interactions, could occur in HFD epididymis. With this in mind, we pointed our attention to QKI, the main FUS partner recently reported to be involved in spermatic backsplicing endogenous skills [ 29 , 35 ]. Effectively, a drastic QKI reduction was observed in HFD epididymis, and in agreement, a strong reduction of FUS–QKI physical interaction occurred.…”

“…In addition, spermatic circRNAs have been identified in human SPZ and appear differentially expressed in relation to sperm morphological quality parameters, as well as to subcellular localization [ 33 ]. In this scenario, a new potential application of circRNAs as biomarkers of sperm quality has been highlighted by profiling a complete dataset of circRNA cargo in asthenozoospermic patients [ 34 ], and not least, a new intriguing role of circRNAs in the modulation of sperm nuclear remodeling dynamics, during their epididymal maturation, has been recently reported [ 35 ].…”