The cell surface hyaluronidase TMEM2 plays an essential role in mouse neural crest cell development and survival
Authors: Inubushi Toshihiro , Nakanishi Yuichiro , Abe Makoto , Takahata Yoshifumi , Nishimura Riko , Kurosaka Hiroshi , Irie Fumitoshi , Yamashiro Takashi , Yamaguchi Yu 
Published: August 2021

Neural crest cells (NCCs) are a migratory population that gives rise to a diverse cell lineage, including the craniofacial complex, the peripheral nervous system, and a part of the heart. Hyaluronan (HA) is a major component of the extracellular matrix, and its tissue levels are dynamically regulated in during development. Although the synthesis of HA has been shown to exert substantial influence on embryonic morphogenesis, the functional importance of the catabolic side of HA turnover is poorly understood. Here, we demonstrate that the transmembrane hyaluronidase TMEM2 plays an essential role in NCC development and the morphogenesis of their derivatives.Wnt1-Cre–mediatedTmem2knockout (Tmem2CKO) mice exhibit severe craniofacial and cardiovascular abnormalities. Analysis ofTmem2expression usingTmem2knock-in reporter mice reveals thatTmem2is expressed at the site of NCC delamination in the neural tube and in Sox9-positive emigrating NCCs, suggesting thatTmem2is critical for NCC development. Consistent with this possibility, linage tracing analysis reveals that the contribution ofWnt1-Cre–labeled cells to NCC derivatives is significantly reduced in aTmem2-deficient background. Moreover, the emigration of NCCs from the neural tube is greatly reduced inTmem2CKOmice.In vitroassays demonstrate thatTmem2expression is essential for the ability of mouse O9-1 NCCs to form focal adhesion on and migrate into HA-containing substrates.Tmem2CKOmice also exhibit increased apoptotic cell death in NCC-derived tissues. Collectively, our data demonstrate thatTmem2is essential for normal development of NCC-derivatives, including the craniofacial complex, and that TMEM2-mediated HA degradation allows NCCs to generate a tissue environment suitable for efficient focal adhesion assembly and migration. This study reveals the hitherto unrecognized functional importance of the catabolic side of HA metabolism in embryonic development and highlights the pivotal role ofTmem2in the process.

Author Summary

The functional significance of hyaluronan (HA) in embryonic developmental processes has been demonstrated by studies using genetic manipulation of HA synthesis. However, the expression of HA is regulated not only by its synthesis, but also by its degradation. This issue is of particular importance due to the extremely rapid metabolic turnover of HA. Curiously, mice with mutations/ablations of known hyaluronidase molecules, such as the lysosomal hyaluronidases HYAL1 and HYAL2, exhibit little embryonic phenotypes. This suggests the existence of yet another hyaluronidase molecule that plays a key role in regulating extracellular HA balance in developing tissues. In this context, transmembrane protein 2 (TMEM2) is a novel hyaluronidase that functions on the cell surface. Here, we demonstrate that TMEM2 is expressed at the site of neural crest development and in neural crest cell (NSC)-derived craniofacial tissue, and that NCC-targetedTmem2conditional knockout mice develop severe craniofacial defects, which attests to a requirement for TMEM2-mediated extracellular HA degradation in neural crest development. Ourin vitroandin vivoanalyses on the underlying mechanisms of the phenotype demonstrate that TMEM2 is essential for generating a tissue environment suitable for efficient focal adhesion formation by NCCs. This paper reveals for the first time that the catabolic machinery for HA exerts a specific regulatory role in embryonic morphogenesis, and that its dysregulation of HA degradation leads to severe developmental defects.