The pituitary gland is an endocrine organ that plays a role in various physiological processes, including growth, metabolism and reproduction. The development of various pituitary endocrine cells is influenced by a number of transcription factors and signals. In this issue (p. 4947), Carmen Birchmeier and colleagues report that the transcription factor Insm1 controls the differentiation of all endocrine cells in the mouse pituitary. The researchers show that Insm1 is expressed in pituitary progenitors and continues to be expressed in differentiated endocrine cells. Using Insm1 knockout mice, they demonstrate that Insm1 controls a pan-endocrine differentiation programme; genes encoding pituitary hormones or proteins involved in hormone production and secretion are downregulated in Insm1 mutant pituitary glands. By contrast, Notch signalling components and skeletal muscle-specific genes are upregulated, suggesting that Insm1 also represses inappropriate gene expression programmes in the pituitary. Finally, the researchers show that the SNAG domain of Insm1 is required for its function, acting to recruit histone-modifying proteins and transcriptional regulators.