Loss of Tctn3 causes neuronal apoptosis and neural tube defects in mice

Bin Wang,Wei Liu,Yingying Zhang,Miao Sun,Man Luo,Hongli Dong,Siyi Gong,Xingshun Xu,Xiaohui Wu,Yufang Zheng,Bin Wei,Hongyan Wang

doi:10.1038/s41419-018-0563-4

Abstract

Tctn3 belongs to the Tectonic (Tctn) family and is a single-pass membrane protein localized at the transition zone of primary cilia as an important component of ciliopathy-related protein complexes. Previous studies showed that mutations in Tctn1 and Tctn2, two members of the tectonic family, have been reported to disrupt neural tube development in humans and mice, but the functions of Tctn3 in brain development remain elusive. In this study, Tctn3 knockout (KO) mice were generated by utilizing the piggyBac (PB) transposon system. We found that Tctn3 KO mice exhibited abnormal global development, including prenatal lethality, microphthalmia, polysyndactyly, and abnormal head, sternum, and neural tube, whereas Tctn3 heterozygous KO mice did not show abnormal development or behaviors. Further, we found that the mRNA levels of Gli1 and Ptch1, downstream signaling components of the Shh pathway, were significantly reduced. Likewise, neural tube patterning-related proteins, such as Shh, Foxa2, and Nkx2.2, were altered in their distribution. Interestingly, Tctn3 KO led to significant changes in apoptosis-related proteins, including Bcl-2, Bax, and cleaved PARP1, resulting in reduced numbers of neuronal cells in embryonic brains. Tctn3 KO inhibited the PI3K/Akt signaling pathway but not the mTOR-dependent pathway. The small molecule SC79, a specific Akt activator, blocked apoptotic cell death in primary mouse embryonic fibroblasts from Tctn3 KO mice. Finally, NPHP1, a protein with anti-apoptotic ability, was found to form a complex with Tctn3, and its levels were decreased in Tctn3 KO mice. In conclusion, our results show that Tctn3 KO disrupts the Shh signaling pathway and neural tube patterning, resulting in abnormal embryonic development, cellular apoptosis, and prenatal death in mice.

Highlights

Loss of a single protein component within a ciliary protein complex disrupts the integrity of that complex and causes defects in the membrane protein composition of the cilia[1,2] that is associated with a group of diseases termed ciliopathies[3], including Joubert syndrome (JBTS), oral-facial-digital syndrome (OFDS), Meckel-Gruber syndrome (MKS), nephronophthisis (NPHP), and Bardet-Biedl syndrome (BBS)
Protein levels of p-mTOR and tmTOR were unchanged in Tctn[3] Het KO mice (P > 0.05, Fig. 5a,b). These results indicate that Shh regulates apoptosis in the brains of Tctn[3] KO mice through a PI3k/ Akt-dependent, mTOR-independent pathway
As Tctn proteins are crucial for ciliogenesis in pMEFs9,10, we further examined whether knockout of

Summary

Introduction

Loss of a single protein component within a ciliary protein complex disrupts the integrity of that complex and causes defects in the membrane protein composition of the cilia[1,2] that is associated with a group of diseases termed ciliopathies[3], including Joubert syndrome (JBTS), oral-facial-digital syndrome (OFDS), Meckel-Gruber syndrome (MKS), nephronophthisis (NPHP), and Bardet-Biedl syndrome (BBS). Among causative genes for these diseases, tectonic mutations have been shown to be important in facilitating ciliopathies[4,5,6,7]. Tectonic (Tctn) family proteins are a group of proteins existing in the cilium transition zone (TZ), including Tctn[1], Tctn[2], and Tctn[38,9]. Owing to the high sequence homology of the three Tctn members, Tctn[3] mutations may share similar phenotypes if the Official journal of the Cell Death Differentiation Association

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Conclusion