Search for regulatory factors of the pituitary-specific transcription factor PROP1 gene

SOX9-positive pituitary stem cells differ according to their position in the gland and maintenance of their progeny depends on context

Stem cell (SC) differentiation and maintenance of resultant progeny underlie cell turnover in many organs, but it is difficult to pinpoint the contribution of either process. In the pituitary, a central regulator of endocrine axes, adult SCs undergo activation after target organ ablation, providing a well-characterized paradigm to study an adaptative response in a multi-organ system. Here, we used single-cell technologies to characterize SC heterogeneity and mobilization together with lineage tracing. We show that SC differentiation occurs more frequently than thought previously. In adaptative conditions, differentiation increases and is more diverse than demonstrated by the lineage tracing experiments. Detailed examination of SC progeny suggests that maintenance of selected nascent cells underlies SC output, highlighting a trophic role for the microenvironment. Analyses of cell trajectories further predict pathways and potential regulators. Our model provides a valuable system to study the influence of evolving states on the mechanisms of SC mobilization.

Retinoic acid signalling is a candidate regulator of the expression of pituitary-specific transcription factor Prop1 in the developing rodent pituitary

Development of the anterior pituitary proceeds via spatiotemporal patterning of transcription factors and signalling molecules. Among them, retinoic acid (RA) functions as an important signalling molecule for vertebrate organogenesis in many tissues. However, little is known regarding the target genes in the developing pituitary. The present study aimed to clarify the relationship between endogenous RA signalling and mRNA expression of the pituitary-specific transcription factor Prop1 in the pituitary primordium of Rathke's pouch. Gene expression analysis and in situ hybridisation demonstrated that retinaldehyde dehydrogenases (Raldhs) and all types of RA receptors (Rars) are expressed at the level of transcription in the rat Rathke's pouch. Ex vivo organ culture using Rathke's pouch and an in vitro reporter assay demonstrated that RA signalling increases the expression level of Prop1 via RARα. Moreover, a reporter assay using serial truncated constructs of the 5'-upstream region of mouse Prop1 revealed a predicted cis-regulatory element of RARα. This is the first report of a relationship between RA signalling and Prop1-expression during early pituitary development.

Involvement of DNA methylation in regulating rat Prop1 gene expression during pituitary organogenesis

PROP1 is a pituitary specific transcription factor that plays a crucial role in pituitary organogenesis. The Prop1 shows varied expression patterns that promptly emerge and then fade during the early embryonic period. However, the regulatory mechanisms governing Prop1 expression remain unclear. Here, we investigated whether Prop1 was under epigenetic regulation by DNA methylation. Bisulfite sequencing was performed on DNA obtained from the pituitary glands and livers of rats on embryonic days (E) 13.5 and E14.5, and postnatal days (P) 4 and P30. The methylation of CpG sites in seven regions from 3-kb upstream of the Prop1 transcription start site through to its second intron were examined. Certain differences in CpG-methylation levels were observed in Region-1 (–2772 b to –2355 b), Region-4 (–198 b to +286 b), Region-5 (+671 b to +990 b), and Region-6 (+1113 b to +1273 b) based on comparisons between pituitary and liver DNA on E13.5. DNA methylation in pituitary glands on E14.5, P4, and P30 was generally similar to that observed in in the pituitary gland on E13.5, whereas the anterior and intermediate lobes of the pituitary gland on P4 and P30 showed only small differences. These results indicate that Prop1 is under regulation by CpG methylation during the early period of pituitary primordium development around E13.5.

Long-chain unsaturated fatty acids reduce the transcriptional activity of the rat follicle-stimulating hormone β-subunit gene

Here, we assessed the effects of long-chain fatty acids (LCFAs) and the LCFA receptor agonist GW9508 on the transcription of the gonadotropin subunit genes Cga, Lhb and Fshb because LCFA receptor GPR120 was observed in mouse gonadotropes in our recent study. A transcription assay using LβT2 cells demonstrated that LCFAs, oleic acid, α-linolenic acid, docosahexaenoic acid and palmitate, repressed the expression of Cga, Lhb, and Fshb at concentrations between 50 and 100 µM. On the other hand, treatment with 10 µM unsaturated LCFAs, oleic acid, α-linolenic acid and docosahexaenoic acid, repressed only Fshb expression, while the same dose of a saturated LCFA, palmitate, had no effect on the expression of gonadotropin subunit genes. Furthermore, GW9508 did not affect promoter activity. Next, we examined deletion mutants of the upstream region of Fshb and found that the upstream regulatory region (-2824 to -2343 bp) of Fshb was responsible for the notable repression by 10 µM unsaturated LCFAs. Our results suggest that the upstream region of Fshb is susceptible to unsaturated LCFAs. In addition, unsaturated LCFAs play a role in repressing Fshb expression through the distal -2824 to -2343 bp region, which might be independent of the LCFA receptor GPR120 pathway.