No abstract

The primary cilium is essential for skin morphogenesis through regulating the Notch, Wnt, and hedgehog signaling pathways. Prior studies on the functions of primary cilia in the skin were based on the investigations of genes that are essential for cilium formation. However, none of these ciliogenic genes has been linked to ciliopathy, a group of disorders caused by abnormal formation or function of cilia. To determine whether there is a genetic and molecular link between ciliopathies and skin morphogenesis, we investigated the role of RPGRIP1L, a gene mutated in Joubert (JBTS) and Meckel (MKS) syndromes, two severe forms of ciliopathy, in the context of skin development. We found that RPGRIP1L is essential for hair follicle morphogenesis. Specifically, disrupting the Rpgril1 gene in mice resulted in reduced proliferation and differentiation of follicular keratinocytes, leading to hair follicle developmental defects. These defects were associated with significantly decreased primary cilium formation and attenuated hedgehog signaling. In contrast, we found that hair follicle induction and polarization and the development of interfollicular epidermis were unaffected. This study indicates that RPGRIP1L, a ciliopathy gene, is essential for hair follicle morphogenesis likely through regulating primary cilia formation and the hedgehog signaling pathway.

Inturned (INTU), a cilia and planar polarity effector (CPLANE), performs prominent ciliogenic functions during morphogenesis, such as in the skin. INTU is expressed in adult tissues but its role in tissue maintenance is unknown. Here, we report that the expression of the INTU gene is aberrantly elevated in human basal cell carcinoma (BCC), coinciding with increased primary cilia formation and activated hedgehog (Hh) signaling. Disrupting Intu in an oncogenic mutant Smo (SmoM2)-driven BCC mouse model prevented the formation of BCC through suppressing primary cilia formation and Hh signaling, suggesting that Intu performs a permissive role during BCC formation. INTU is essential for IFT-A complex assembly during ciliogenesis. To further determine whether Intu is directly involved in the activation of Hh signaling downstream of ciliogenesis, we examined the Hh signaling pathway in mouse embryonic fibroblasts, which readily respond to Hh pathway activation. Depleting Intu blocked SAG-induced Hh pathway activation, whereas the expression of Gli2ΔN, a constitutively active Gli2, restored Hh pathway activation in Intu-deficient cells, suggesting that INTU functions upstream of Gli2 activation. In contrast, overexpressing Intu did not promote ciliogenesis or Hh signaling. Taken together, data obtained from this study suggest that INTU is indispensable during BCC tumorigenesis and that its aberrant upregulation is likely a prerequisite for primary cilia formation during Hh-dependent tumorigenesis.

GORAB is a golgin that localizes predominantly at the Golgi apparatus and physically interacts with small GTPases. GORAB is ubiquitously expressed in mammalian tissues, including the skin. However, the biological function of this golgin in skin is unknown. Here, we report that disrupting the expression of the Gorab gene in mice results in hair follicle morphogenesis defects that were characterized by impaired follicular keratinocyte differentiation. This hair follicle phenotype was associated with markedly suppressed hedgehog (Hh) signaling pathway in dermal condensates in vivo. Gorab-deficient dermal mesenchymal cells also displayed significantly reduced capability to respond to Hh pathway activation in vitro. Furthermore, we found that the formation of primary cilium, a cellular organelle that is essential for the Hh pathway, was impaired in mutant dermal papilla cells, suggesting that Gorab may be required for the Hh pathway through facilitating the formation of primary cilia. Thus, data obtained from this study provided insight onto the biological functions of Gorab during embryonic morphogenesis of skin in which Hh signaling and primary cilia exert important functions.

In 2009, a novel swine-origin H1N1 influenza virus emerged in Mexico and quickly spread to other countries, including China. This 2009 pandemic H1N1 can cause human respiratory disease, but its pathogenesis remains poorly understood. Here, we studied the infection and pathogenesis of a new 2009 pandemic strain, A/Wenshan/01/2009 H1N1, in China in human airway epithelial cell lines compared with contemporary seasonal H1N1 influenza virus. Our results showed that viral infection by the A/Wenshan H1N1 induced significant apoptotic cell death in both the human nasopharyngeal carcinoma cell line CNE-2Z and the human lung adenocarcinoma cell line A549. The A/Wenshan H1N1 virus enters both of these cell types more efficiently than the seasonal influenza virus. Viral entry in both cell lines was shown to be mediated by clathrin- and dynamin-dependent endocytosis. Therefore, we discovered that the 2009 pandemic H1N1 strain, A/Wenshan/01/2009, can induce apoptotic cell death in epithelial cells of the human respiratory tract, suggesting a molecular pathogenesis for the 2009 pandemic H1N1.