Background: Mouse studies have demonstrated the necessity of Sonic Hedgehog (SHH) for normal proliferation of Rathkes pouch (RP) precursors. However, the possible function of SHH in pituitary cell specification remains to be assessed. Additionally, evidence suggests that SHH may be relevant in human adamantinomatous craniopharyngioma (ACP), a histologically benign, but clinically aggressive childhood tumour associated with high morbidity.
Objective and Hypotheses: To determine the function of SHH during normal pituitary development and in human ACP. Specifically, we aim to test whether:
i) SHH is relevant for cell specification during pituitary development. ii) SHH is expressed in human ACP and involved in its pathogenesis.
Method: i) Conditional deletion of Shh in the developing pituitary and ii) murine models of human ACP as well as chemical inhibition of Shh in the ACP models.
Results: We firstly show that the conditional deletion of Shh in the hypothalamus causes a severe arrest of RP development with complete loss of pituitary tissue by 12.5 days post coitum. Molecular analyses have shown that Shh is not only required for normal proliferation as previously suggested, but in addition, its plays a critical role in the specification of RP precursors. In the absence of hypothalamic SHH signalling, expression of Lhx3 and Lhx4 is not activated, whilst Islet 1 and Pitx1 are normally expressed in RP. Secondly, we show by in situ hybridisation analysis on more than 20 ACP samples that SHH is expressed in the β-catenin-accumulating cell clusters, whilst PTCH1, a direct target of the pathway, is expressed in surrounding tumour cells. Moreover, using a novel multiple-reaction-monitoring tandem mass spectrometry-based assay, SHH protein is detected in human ACP, strongly suggesting that biologically active SHH is present within the tumours.
Conclusion: SHH is required for cell specification of RP precursors and is expressed in human ACP.
18 Sep 2014 - 20 Sep 2014