Quantifying DYRK1A during perinatal development in the hippocampus, cerebral cortex, and cerebellum of the Ts65Dn mouse model

The relationship between gene copy number and protein expression levels has not thoroughly been examined in humans or mouse models of Down syndrome (DS) in relationship to developmental changes in the trisomic brain. Found on human chromosome 21 (Hsa21) and triplicated in DS, Dual-specificity tyrosine-phosphorylated regulated kinase 1A (DYRK1A) has been linked in DS to neurological deficits by restricting cell growth and proliferation. Little information exists regarding DYRK1A during perinatal development and how its expression may lead to cognitive deficits, and none exists that explores the gene-to-protein relationship during these critical time periods. This study aims to 1) Quantify variable DYRK1A expression across development as a function of age, sex, and brain region in trisomic Ts65Dn mice compared to euploid counterparts and 2) establish that the spatiotemporal pattern of developmental DYRK1A in the brain is not influenced solely by gene copy number, and that reduction of Dyrk1a in euploid and trisomic mice does not result in a corresponding global reduction of DYRK1A expression. DYRK1A was quantified in three areas of the postnatal brain at seven ages using the Ts65Dn mouse, the most studied model of DS, and found that trisomic expression is significantly increased on postnatal day ([P]6), declining by the third week to near euploid levels. We also uncovered a sexual dimorphic expression of DYRK1A when comparing animals of different sexes within the same genotype. Data from Dyrk1a knockdown mice indicated that reducing only Dyrk1a in euploid and in otherwise trisomic animals yields highly variable levels of DYRK1A, dependent on sex and tissue type, supporting the non-intuitive relationship between gene dosage and protein expression. These data emphasize the need to understand the age-dependent regulation of antecedent conditions that are causing changes in Dyrk1a expression in the brain.