A critical role for the nuclear protein Akirin2 in the formation of mammalian muscle in vivo

Abstract

Summary Evolutionarily conserved Akirin nuclear proteins interact with chromatin remodeling complexes at gene enhancers and promoters, and have been reported to regulate cell proliferation and differentiation. Of the two mouse Akirin genes, Akirin2 is essential during embryonic development, with known in vivo roles in immune system function and the formation of the cerebral cortex. Here we demonstrate that Akirin2 is critical for mouse myogenesis, a tightly regulated developmental process through which myoblast precursors fuse to form mature skeletal muscle fibers. Loss of Akirin2 in somitic muscle precursor cells via Sim1‐Cre‐mediated excision of a conditional Akirin2 allele results in neonatal lethality. Mutant embryos exhibit a complete lack of forelimb, intercostal, and diaphragm muscles due to extensive apoptosis and loss of Pax3‐positive myoblasts. Severe skeletal defects, including craniofacial abnormalities, disrupted ossification, and rib fusions are also observed, attributable to lack of skeletal muscles as well as patchy Sim1‐Cre activity in the embryonic sclerotome. We further show that Akirin2 levels are tightly regulated during muscle cell differentiation in vitro, and that Akirin2 is required for the proper expression of muscle differentiation factors myogenin and myosin heavy chain. Our results implicate Akirin2 as a major regulator of mammalian muscle formation in vivo.

p53-mediated neurodegeneration in the absence of the nuclear protein Akirin2

“…Interestingly, mRNA levels assessed by qPCR at a sampling of ages remained consistent throughout development in contrast to Aki2 protein levels (Figure 1C). This is consistent with our prior work utilizing muscle cells as well as with a developmental mouse cortex transcriptomic dataset (Fertuzinhos et al, 2014;Bosch et al, 2019) and suggests that Aki2 protein is post-transcriptionally regulated during brain maturation. Furthermore, close inspection of western blots at a variety of exposures revealed 3 distinct bands of ~22kDa, 25kDa, and 27kDa, as well as two higher molecular weight bands of ~33kDa and ~35kDa.…”

“…Cell death and glial activation moves from the cortical layers with the greatest number of Aki2 null cells and progresses to primarily Cre-negative layers providing evidence that primary cell death occurs in Aki2-null neurons cell-autonomously followed by secondary cell-non-autonomous death in neurons that retain Aki2. Interestingly, unlike the apoptosis reported in embryonic Aki2-null cortical progenitors (Bosch et al, 2016) and muscle progenitors (Bosch et al, 2019) we present extensive convergent evidence that Aki2-null postmitotic neurons die via necroptosis in a p53-dependent manner. Our transcriptomic analyses also support this conclusion, as both mutant neural progenitor and postmitotic neuron transcriptomes were enriched for upregulated p53 target genes.…”

“…Furthermore, close inspection of western blots at a variety of exposures revealed 3 distinct bands of ~22kDa, 25kDa, and 27kDa, as well as two higher molecular weight bands of ~33kDa and ~35kDa. Knockout and knockdown validation of the primary antibody used here (Bosch et al, 2018;Bosch et al, 2019), confirmed that all 5 of these bands are specific to Aki2. This suggests that the cortex expresses several post-translationally modified forms and/or unannotated Aki2 splice variants.…”

“…For qPCR validation studies, RNA (90-100ng) collected from E10.5 telencephalon was reverse transcribed using the High Capacity RNA-to-cDNA kit and qPCR performed as above using the primers listed in Table S2. The ddC(t) method was used to calculate fold change using -Actin as a reference gene as described previously (Bosch et al, 2019).…”

Akirin Is Required for Muscle Function and Acts Through the TGF-β Sma/Mab Signaling Pathway inCaenorhabditis elegansDevelopment

“…in porcine and mouse muscle cells and conditional knockout of Akirin2 perturbed muscle development in vivo in the mouse (Chen et al 2017;Bosch et al 2019). Akirin2, but not Akirin1, was also studied in the context of tumor promotion.…”