Post-natal development of brown adipocytes in white fat: Phases independent and dependent of the ambient temperature

Decreased ambient temperature, from birth to weaning, significantly reduced fat mass (FM) and adiposity in developing mice. Changes in FM content in 10 day-old mice raised at 17°C were not accompanied by precocious induction of brown adipocytes in inguinal white adipose tissue (WAT). Brown phenotype was induced in 21 day-old mice independently of ambient temperature (17°C or 29°C) however the expression of Ucp1 and other brown fat biomarker genes was greater in animals raised at 17°C suggesting increased adaptive thermogenesis. Accordingly, we predict that the induction of brown adipocytes in WAT follows a strict developmental program and the number of potential brown adipocytes in WAT is determined genetically. Microarray analysis of gene expression was performed on inguinal white adipose tissue dissected from 10 and 21 day-old mice kept at different temperature conditions, that is, in mice maintained at 17°C or 29oC during early post-natal development.