Pituitary Phenotypes of Mice Lacking the Notch Signalling Ligand Delta‐Like 1 Homologue

The Notch signalling pathway ligand delta‐like 1 homologue ( D lk1, also named Pref1) is expressed throughout the developing pituitary and becomes restricted to mostly growth hormone ( GH ) cells within the adult gland. We have investigated the role of D lk1 in pituitary development and function from late embryogenesis to adulthood using a mouse model completely lacking the expression of D lk1. We confirm that D lk1‐null mice are shorter and weigh less than wild‐type littermates from late gestation, at parturition and in adulthood. A loss of D lk1 leads to significant reduction in GH content throughout life, whereas other pituitary hormones are reduced to varying degrees depending on sex and age. Both the size of the pituitary and the proportion of hormone‐producing cell populations are unchanged, suggesting that there is a reduction in hormone content per cell. In vivo challenge of mutant and wild‐type littermates with growth hormone‐releasing hormone and growth hormone‐releasing hexapeptide shows that reduced GH secretion is unlikely to account for the reduced growth of D lk1 knockout animals. These data suggest that loss of Dlk1 gives rise to minor pituitary defects manifesting as an age‐ and sex‐dependent reduction in pituitary hormone contents. However, D lk1 expression in other tissue is most likely responsible for the weight and length differences observed in mutant animals.