ScRNAseq Analysis of Chicken Embryonic Pituitary Reveals Cell Heterogeneity and a Cell Type Coexpressing <i>Gh</i> and <i>Pomc</i>

Gene expression profiles and the heterogeneity among hormone-producing pituitary cells remain poorly characterized in most vertebrates, especially in chicken embryos. Using single-cell RNA sequencing, the transcriptomes of 4346 basal and 10 835 corticosterone (CORT)-treated embryonic day 11 chicken pituitary cells were sequenced. Classical endocrine cell clusters were identified, and some were shown to express previously unreported marker genes. A cluster of uncommitted cells was identified that expressed markers for multiple endocrine cell types, with ∼30% coexpressing Gh and Pomc mRNA. We named this population of cells the cortico-somatotrophs. The existence of cortico-somatotrophs were confirmed at both the mRNA and protein level. We further characterized the corticosomatotrophs by utilizing the known effect of CORT to increase somatotroph abundance. Identification of cortico-somatotrophs challenges the prevailing view that corticotrophs and somatotrophs develop from distinct cell lineages.