A Targeting Mutation of Tyrosine 1062 in Ret Causes a Marked Decrease of Enteric Neurons and Renal Hypoplasia

Abstract

The Ret receptor tyrosine kinase plays a crucial role in the development of the enteric nervous system and the kidney. Tyrosine 1062 in Ret represents a binding site for the phosphotyrosine-binding domains of several adaptor and effector proteins that are important for the activation of intracellular signaling pathways, such as the RAS/ERK, phosphatidylinositol 3-kinase/AKT, and Jun-associated N-terminal kinase pathways. To investigate the importance of tyrosine 1062 for organogenesis in vivo, knock-in mice in which tyrosine 1062 in Ret was replaced with phenylalanine were generated. Although homozygous knock-in mice were born normally, they died by day 27 after birth and showed growth retardation. The development of the enteric nervous system was severely impaired in homozygous mutant mice, about 40% of which lacked enteric neurons in the whole intestinal tract, as observed in Ret-deficient mice. The rest of the mutant mice developed enteric neurons in the intestine to various extents, although the size and number of ganglion cells were significantly reduced. Unlike Ret-deficient mice, a small kidney developed in all knock-in mice, accompanying a slight histological change. The reduction of kidney size was due to a decrease of ureteric bud branching during embryogenesis. Thus, these findings demonstrated that the signal via tyrosine 1062 plays an important role in histogenesis of the enteric nervous system and nephrogenesis.

GDNF/Ret signaling and the development of the kidney

“…In vivo, hypomorphic mutations in Ret (or heterozygosity for GDNF null mutations) that reduce but do not eliminate GDNF/Ret signaling result in hypodysplastic kidneys, apparently because they reduce the rate of growth and/ or branching of the UB. (30,60,61) The same is true of mutations in retinoic acid receptors, whose expression is required for the maintenance of Ret expression, and which can be rescued by forced expression of Ret in the UB. (10) Addition of GDNF to kidney cultures can increase the number of UB tips, which suggested a stimulation of branching.…”

Evaluation of potential mechanisms underlying genotype–phenotype correlations in multiple endocrine neoplasia type 2

“…Thus, we analysed the impact of different RET mutations on key molecules involved in signal transduction. Phosphorylation of tyrosine residue 1062 is an essential hallmark of RET transforming activity (Asai et al, 1996;Jijiwa et al, 2004). As shown in Figure 4a, the MEN 2B mutations M918T and A883F caused highly elevated phosphorylation of tyrosine residue 1062, whereas the other mutant RET proteins display equal amounts of low-level tyrosine phosphorylation.…”

Gdnf signaling pathways within the mammalian spermatogonial stem cell niche

“…These residues can serve as intracellular docking sites to many different SH2 domain-containing proteins, including Src. While Src interacts with Ret at Tyr 981 (Encinas et al, 2004), Tyr 1062 serves as a docking site to most other effectors and triggers the activation of the Ras signaling pathway in the developing enteric nervous system, the developing kidney, and also in neuroblastoma (Worby et al, 1996;Jijiwa et al, 2004;Hayashi et al, 2000). Therefore, we examined whether Gdnf can activate Ras signaling in SSCs (He et al, 2008).…”