# Mutations in Filamin C Associated with Both Alleles Do Not Affect the Functioning of Mice Cardiac Muscles

## TL;DR

Mice with specific mutations in the FLNC gene show normal heart function and even improved grip strength compared to normal mice.

## Contribution

The study reveals that compound heterozygous FLNC mutations in mice do not impair cardiac function and may even enhance physical performance.

## Key findings

- Homozygous FLNC mutations in mice are embryonically lethal, but compound heterozygous mice are viable and develop normally.
- Compound heterozygous mice show normal cardiac function and better grip strength than wild-type mice.
- A structural model explains how two FLNC mutations may complement each other.

## Abstract

Filamin C (FLNC) is a structural protein of muscle fibers. Mutations in the FLNC gene are known to cause myopathies and cardiomyopathies in humans. Here we report the generation by a CRISPR/Cas9 editing system injected into zygote pronuclei of two mouse strains carrying filamin C mutations—one of them (AGA) has a deletion of three nucleotides at position c.7418_7420, causing E>>D substitution and N deletion at positions 2472 and 2473, respectively. The other strain carries a deletion of GA nucleotides at position c.7419_7420, leading to a frameshift and a premature stop codon. Homozygous animals (FlncAGA/AGA and FlncGA/GA) were embryonically lethal. We determined that FlncGA/GA embryos died prior to the E12.5 stage and illustrated delayed development after the E9.5 stage. We performed histological analysis of heart tissue and skeletal muscles of heterozygous strains carrying mutations in different combinations (FlncGA/wt, FlncAGA/wt, and FlncGA/AGA). By performing physiological tests (grip strength and endurance tests), we have shown that heterozygous animals of both strains (FlncGA/wt, FlncAGA/wt) are functionally indistinguishable from wild-type animals. Interestingly, compound heterozygous mice (FlncGA/AGA) are viable, develop normally, reach puberty and it was verified by ECG and Eco-CG that their cardiac muscle is functionally normal. Intriguingly, FlncGA/AGA mice demonstrated better results in the grip strength physiological test in comparison to WT animals. We also propose a structural model that explains the complementary interaction of two mutant variants of filamin C.