# Impact of maternal compensation on developmental phenotypes in a zebrafish model of severe congenital muscular dystrophy

## TL;DR

The study shows how maternal compensation affects disease modeling in zebrafish, with maternal-zygotic mutants better replicating human congenital muscular dystrophy features.

## Contribution

The study introduces a zebrafish model of CMD that demonstrates the impact of maternal compensation on disease progression and gene expression.

## Key findings

- Offspring from mutant mothers show early-onset muscle disease and neurological deficits similar to human CMD.
- Maternal compensation influences offspring gene expression, including metabolic changes.
- Maternal-zygotic mutants provide a more accurate model for human CMD compared to zygotic-only mutants.

## Abstract

Genetic compensation is a common phenomenon in zebrafish in response to genetic alterations. Differences between genetic and morpholino-mediated zebrafish models of human diseases have led to significant difficulties in phenotypic interpretation and translatability. One form of compensation is the maternal deposit of mRNAs and proteins to the oocyte that supports developmental processes before zygotic genome activation. In this study, we generated a zebrafish model of severe congenital muscular dystrophy (CMD) by targeting protein O-mannose N-Acetylglucosaminyltransferase 2 (pomgnt2), a maternally provided gene that maintains cell-extracellular matrix interactions through glycosylation and leads to congenital muscular dystrophy when mutated. Zygotic knockouts (ZKOs) retain protein function in the first week post fertilization and survive to adulthood, only developing muscle disease later in life. In contrast, maternal-zygotic KOs (MZKOs) generated from ZKO females develop early-onset muscle disease, reduced motor function, neuronal axon guidance deficits, and retinal synapse disruptions recapitulating features of the human presentation. While assessing transcriptional changes linked to disease progression, the availability of embryos obtained from different breeding strategies also allowed for a direct comparison of ZKOs and MZKOs to define the impact of having a KO mother. We found that offspring from a ZKO mother, independently of genotype, show distinct expression patterns from animals obtained from heterozygous breedings. Some of these changes reflect changes in metabolic function, possibly stemming from maternal metabolic disruption. These findings will not only be applicable for other CMD models targeting maternally provided genes, but also provide new insight into modeling disease using maternal-zygotic mutants.

Generating zebrafish genetic mutants that exhibit similar features to human diseases can be complicated. Unlike humans, zebrafish are highly equipped to compensate for genetic mutations. As a result, mutant zebrafish are often healthy or show signs of disease much later in their lifespan. In this study, we generated a zebrafish strain with mutations in a gene that causes congenital muscular dystrophy, but due to compensation from healthy female parents, the mutant offspring do not show signs of disease until adulthood. Mutant female parents, however, cannot compensate, so their mutant offspring have disease early in life, like humans. Using mutant females to generate mutant offspring helped us study how the disease progresses in the muscles and nervous system. We also showed that this approach could impact the metabolism of these offspring compared to the offspring of healthy females. This finding is highly important, as many other mutant zebrafish designed to model human genetic disorders show the same compensation. Therefore, fully understanding this compensation will also advance our understanding of other zebrafish genetic models of disease.