C57bl 6 j c57

All the experiments were approved by the local ethics committee Malmö/Lund region and specified in permit 4992/2022. Male mice were housed under a 12-h Light: Dark cycle with free access to food and water. Wild-type (WT) Females for the Oncins France 1 (OF1) and C57Bl/6 J (C57) strains were obtained from Charles River Laboratories, France, and mated with En1^+/− males (C57-En1^+/− and OF1-En1^+/−). OF1-En1^+/− were generated as described earlier (Sonnier et al., 2007 (link)). C57-En1^+/− mice were generated by repeated backcrossing (>10 generations) of OF1-En1^+/− to the C57 background (Van Andel Institute, MI, United States). Mice were sacrificed at 4 different ages: 1, 4, and 16 weeks. Seven mice per genotype and strain were used for histological analysis. As for RNA-Seq, 6 mice from each strain were used, of which 3 were WT and 3 En1^+/−. Exclusively male mice were used in this study. Four groups of male mice were studied to assess both En1^+/− and genetic background effects (Figure 1A).

Male C57BL/6J (C57, n = 16, Charles River, UK), DBA/2J (DBA, n = 16, Harlan, UK) and CD1 (n = 15, Charles River, UK) mice were 7–9 weeks old at the start of behavioural procedures. Mice were housed between one and four per cage, in a holding room with a 12-h light cycle (lights off at 7 AM). All experiments were performed during the dark cycle. After a minimum of 7 days of acclimatisation to the animal facility, food was restricted to maintain 85–90 % of free feeding body weight with ad libitum drinking water throughout the experiments. During food restriction, reward pellets (14 mg Bio-Serv purified rodent dustless precision pellets through Sandown Scientific) were introduced in the home cage for minimum 3 days to decrease neophobia to the rewards during training. All experiments were in compliance with the United Kingdom Animals (Scientific Procedures) Act (1986).