Transcriptome analyses of somatotropes and lactotropes reveal novel regulators of cell identity in the pituitary

The differentiation of the hormone-producing cell lineages of the anterior pituitary represents an informative model of mammalian cell fate determination. The generation and maintenance of two of these lineages, the growth hormone (GH) producing somatotropes and prolactin (PRL) producing lactotropes, is dependent on the pituitary-specific POU-homeo domain transcription factor, POU1F1. While POU1F1 is expressed in both cell types, and plays a direct and essential role in the activation of both the Gh and Prl genes, GH expression is restricted to somatotropes and PRL expression is restricted to lactotropes. These observations imply the existence of additional, cell type-enriched factors, that contribute to the somatotrope and lactotrope cell identities. Here, we use a set of transgenic mouse models to facilitate sorting of somatotrope and lactotrope populations based on the expression of distinct fluorescent markers expressed under Gh and Prl gene transcriptional controls, respectively. The transcriptomic analyses reveal a concordance of gene expression profiles in the two populations. The limited number of divergent mRNAs between the two populations includes a set of transcription factors that may have roles in pituitary lineage divergence or in regulating the expression of key lineage-specific genes after lineage divergence. Four of these factors were validated for lineage enrichment at the level of protein expression, two somatotrope-enriched and two lactotrope-enriched, and three of these four factors were shown to have corresponding activities in appropriate enhancement or repression of landmark genes. These studies establish a useful database for further study of the somatotrope and lactotrope cells as well as identify novel regulators of lineage marker expression in the anterior pituitary. Overall design: 6 total samples, 3 biological replicates of the somatotrope cell type and 3 biological replicates of the lactotrope cell type

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Peel MT, Ho Y, Liebhaber SA