Effect of retinoic acid on midkine gene expression in rat anterior pituitary cells

Expression of Retinaldehyde Dehydrogenases in the Pituitary Glands of Fetus and Adult Mice

Retinoic acid (RA) plays a critical role in cell growth and tissue development. RA is synthesized from retinoids through oxidation processes by the retinaldehyde dehydrogenase (Raldh) family. However, the expression of Raldhs during pituitary development and the identification of Raldh-expressing cells in the adult pituitary have not been fully elucidated. Here, we performed in situ hybridization to localize the three Raldh isoforms (Raldh1-3) in fetal and adult mouse pituitary glands. The results showed that Raldh2 expression was observed in Rathke's pouch from embryonic day 13.5 (E13.5), and this expression was sustained in the anterior lobe of the pituitary primordium from E15.5 to E17.5. In contrast, Raldh1 and Raldh3 were rarely detectable. Real-time PCR analysis revealed that Raldh2 was the predominant isoform expressed in the adult pituitary, although Raldh1 was also expressed to a lesser extent. In the adult pituitary, Raldh1-expressing cells were primarily observed in the posterior lobe. Raldh2-expressing cells were found in the marginal cell layer and parenchyma of the anterior lobe and were immunopositive for aldolase C (folliculostellate cells), but not for anterior pituitary hormones. These results suggest that RA is an important regulatory factor in the functions of the pituitary throughout its development in mice.

Single-Cell RNA Sequencing Analysis of Chicken Anterior Pituitary: A Bird's-Eye View on Vertebrate Pituitary

It is well-established that anterior pituitary contains multiple endocrine cell populations, and each of them can secrete one/two hormone(s) to regulate vital physiological processes of vertebrates. However, the gene expression profiles of each pituitary cell population remains poorly characterized in most vertebrate groups. Here we analyzed the transcriptome of each cell population in adult chicken anterior pituitaries using single-cell RNA sequencing technology. The results showed that: (1) four out of five known endocrine cell clusters have been identified and designated as the lactotrophs, thyrotrophs, corticotrophs, and gonadotrophs, respectively. Somatotrophs were not analyzed in the current study. Each cell cluster can express at least one known endocrine hormone, and novel marker genes (e.g., CD24 and HSPB1 in lactotrophs, NPBWR2 and NDRG1 in corticotrophs; DIO2 and SOUL in thyrotrophs, C5H11ORF96 and HPGDS in gonadotrophs) are identified. Interestingly, gonadotrophs were shown to abundantly express five peptide hormones: FSH, LH, GRP, CART and RLN3; (2) four non-endocrine/secretory cell types, including endothelial cells (expressing IGFBP7 and CFD) and folliculo-stellate cells (FS-cells, expressing S100A6 and S100A10), were identified in chicken anterior pituitaries. Among them, FS-cells can express many growth factors, peptides (e.g., WNT5A, HBEGF, Activins, VEGFC, NPY, and BMP4), and progenitor/stem cell-associated genes (e.g., Notch signaling components, CDH1), implying that the FS-cell cluster may act as a paracrine/autocrine signaling center and enrich pituitary progenitor/stem cells; (3) sexually dimorphic expression of many genes were identified in most cell clusters, including gonadotrophs and lactotrophs. Taken together, our data provides a bird's-eye view on the diverse aspects of anterior pituitaries, including cell composition, heterogeneity, cell-to-cell communication, and gene expression profiles, which facilitates our comprehensive understanding of vertebrate pituitary biology.