Investigating sex differences in DDX3X mouse models

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Abstract De novo mutations in the RNA binding protein DDX3X result in DDX3X syndrome. DDX3X mutations are also associated with autism spectrum disorder (ASD) and may account for 1-3% of unexplained developmental delay (DD) in females. Yet, our understanding of DDX3X function in the developing brain is limited. Our funded grant aims to understand the mechanisms by which DDX3X loss of function and missense mutations perturb cellular function. This supplement will focus on sexually dimorphic phenotypes linked to DDX3X. Most de novo mutations are in DDX3X females though increasing numbers of cases in males have been observed. We have discovered that complete loss of Ddx3x in females causes striking microcephaly. In contrast, complete knockout in males phenocopies haploinsufficiency in females. Our data suggest that these differences between males and females may be due to altered expression of the paralog, Ddx3y. In this supplement, we will test the hypothesis that phenotypic differences in males and females associated with Ddx3x loss are due to compensation by the paralog, Ddx3y. To test this, we will use single cell transcriptomics to quantify cell composition and transcriptome changes associated with Ddx3x loss in males and female embryonic brains. Additionally, we will use knockdown and rescue experiments to test the functional redundancy of Ddx3y and Ddx3x for embryonic brain development. These experiments will give valuable new insights to understand roles for Ddx3x in neurogenesis at a cellular and molecular level. Importantly, this proposal is designed to give fundamental experimental training in mouse genetics, embryology, sequencing, histology and microscopy. This supplement also includes a comprehensive mentoring plan for career development.