Antibodies used in this study.

<div><p>Brown adipose tissue (BAT) thermogenesis is pivotal for maintaining body temperature and energy balance. Mitochondrial morphology is dynamically controlled by a balance between fusion and fission, which is crucial for cell differentiation, response to metabolic insults, and heat production. Dynamin-related protein 1 (Drp1) is a key regulator of mitochondrial fission. This study investigates the role of Drp1 in BAT development and thermogenesis by generating Drp1-deficient mice. These mice were created by crossing Drp1 floxed mice with fatty acid-binding protein 4-Cre (<i>aP2</i>-Cre) transgenic mice, resulting in <i>aP2</i>-Cre<sup>+/-</sup><i>Drp1</i><sup>flox/flox</sup> (<i>aP2-Drp1</i><sup>f/f</sup>) mice. The <i>aP2-Drp1</i><sup>f/f</sup> mice exhibited severe BAT and brain hypoplasia, with the majority dying within 48 hours postnatally, highlighting Drp1’s crucial role in neonatal survival. Impaired thermogenic responses were observed in <i>aP2-Drp1</i><sup>f/f</sup> mice, characterized by significantly decreased expression of thermogenic and lipogenic genes in BAT. Ultrastructural analysis revealed disrupted mitochondrial morphology and reduced lipid droplet content in BAT. The few surviving adult <i>aP2-Drp1</i><sup>f/f</sup> mice also showed impaired BAT and brain development, along with BAT thermogenesis dysfunction during cold exposure. Our findings underscore the essential role of Drp1-mediated mitochondrial fission in BAT thermogenesis and neonatal survival, providing insights into potential therapeutic approaches for metabolic disorders.</p></div>