DAAM1 and DAAM2 are co-required for myocardial maturation and sarcomere assembly

AbstractWnt ligands regulate heart morphogenesis but the underlying mechanisms remain unclear. Two Formin-related proteins, DAAM1 and 2, were previously found to bind the Wnt effector Disheveled. Here, since DAAM1 and 2 nucleate actin and mediate Wnt-induced cytoskeletal changes, a floxed-allele of Daam1 was used to disrupt its function specifically in the myocardium and investigate Wnt-associated pathways. Homozygous Daam1 conditional knockout (CKO) mice were viable but had misshapen hearts and poor cardiac function. The defects in Daam1 CKO mice were observed by mid-gestation and were associated with a loss of protrusions from cardiomyocytes invading the outflow tract. Further, these mice exhibited noncompaction cardiomyopathy (NCM) and deranged cardiomyocyte polarity. Interestingly, Daam1 CKO mice that were also homozygous for an insertion disrupting Daam2 (DKO) had stronger NCM, severely reduced cardiac function, disrupted sarcomere structure, and increased myocardial proliferation, suggesting that DAAM1 and DAAM2 have redundant functions. While RhoA was unaffected in the hearts of Daam1/2 DKO mice, AKT activity was lower than in controls, raising the issue of whether DAAM1/2 are only mediating Wnt signaling. Daam1-floxed mice were thus bred to Wnt5a null mice to identify genetic interactions. The hearts of Daam1 CKO mice that were also heterozygous for the null allele of Wnt5a had stronger NCM and more severe loss of cardiac function than Daam1 CKO mice, consistent with DAAM1 and Wnt5a acting in a common pathway. However, deleting Daam1 further disrupted Wnt5a homozygous-null hearts, suggesting that DAAM1 also has Wnt5a-independent roles in cardiac development

薬剤誘導性遺伝子ノックアウト法を用いた細胞極性制御機構の解析

金沢大学医薬保健研究域医学系本研究ではaPKCとDaam1の2種類の細胞極性関連遺伝子のコンディショナル・ノックアウトマウスを用いて、薬剤誘導下で遺伝子ノックアウトが可能な実験系を構築した。マウスの発生過程での表現型解析、上皮の初代培養系における解析を行い、aPKC-Daam1の遺伝学的な相互作用を検出した。さらにアフリカツメガエルを用いた遺伝子ノックダウン・レスキュー法を用いた解析によりaPKCの作用点がDaam1の下流であることを示唆する結果を得た。In this study, we constructed novel experimental system, which enable us to disrupt gene function under the control of Tamoxifen by using Cre-loxP technology. We focused on two polarity related genes, aPKC(atypical Protein kinase C) and Daam1(Deshevelled associated activator of morphogenesis), and successfully detected genetic interaction and cellular phenotype. Further, we confirmed this results by using Xenopus injection experiment and found the possibility that aPKC acts as down stream of Daam1.研究課題/領域番号:21790177, 研究期間(年度):2009-2010出典：研究課題「薬剤誘導性遺伝子ノックアウト法を用いた細胞極性制御機構の解析」課題番号21790177（KAKEN：科学研究費助成事業データベース（国立情報学研究所）） （https://kaken.nii.ac.jp/ja/report/KAKENHI-PROJECT-21790177/21790177seika/）を加工して作

Placental defects lead to embryonic lethality in mice lacking the Formin and PCP proteins Daam1 and Daam2.

The actin cytoskeleton plays a central role in establishing cell polarity and shape during embryonic morphogenesis. Daam1, a member of the Formin family of actin cytoskeleton regulators, is a Dvl2-binding protein that functions in the Wnt/Planar Cell Polarity (PCP) pathway. To examine the role of the Daam proteins in mammalian development, we generated Daam-deficient mice by gene targeting and found that Daam1, but not Daam2, is necessary for fetal survival. Embryonic development of Daam1 mutants was delayed most likely due to functional defects in the labyrinthine layer of the placenta. Examination of Daam2 and Daam1/2 double mutants revealed that Daam1 and Daam2 are functionally redundant during placental development. Of note, neural tube closure defects (NTD), which are observed in several mammalian PCP mutants, are not observed in Wnt5a or Daam1 single mutants, but arise in Daam1;Wnt5a double mutants. These findings demonstrate a unique function for Daam genes in placental development and are consistent with a role for Daam1 in the Wnt/PCP pathway in mammals