Diverse functions of kindlin/fermitin proteins during embryonic development in Xenopus laevis

Kindlin-2 in myoepithelium controls luminal progenitor commitment to alveoli in mouse mammary gland

Myoepithelium plays an important role in mammary gland development, but less is known about the molecular mechanism underlying how myoepithelium controls acinus differentiation during gestation. Herein, we found that loss of Kindlin-2 in myoepithelial cells impaired mammary morphogenesis, alveologenesis, and lactation. Using five genetically modified mouse lines combined with single-cell RNA sequencing, we found a Kindlin-2-Stat3-Dll1 signaling cascade in myoepithelial cells that inactivates Notch signaling in luminal cells and consequently drives luminal progenitor commitment to alveolar cells identity. Single-cell profiling revealed that Kindlin-2 loss significantly reduces the proportion of matured alveolar cells. Mechanistically, Kindlin-2 depletion in myoepithelial cells promotes Stat3 activation and upregulates Dll1, which activates the Notch pathway in luminal cells and inhibits luminal progenitor differentiation and maturation during gestation. Inhibition of Notch1 with tangeretin allowed luminal progenitors to regain commitment ability in the pregnant mice with Kindlin-2 depletion in myoepithelium. Taken together, we demonstrated that Kindlin-2 is essential to myoepithelium-controlled luminal progenitors to alveoli transition during gestation.

[Kindlin-2 regulates endometrium development via mTOR and Hippo signaling pathways in mice]

OBJECTIVE

To investigate the effects and mechanisms of Kindlin-2 on uterus development and reproductive capacity in female mice.

METHODS

Cdh16-Cre tool mice and Kindlin-2^flox/flox mice were used to construct the mouse model of uterus specific knockout of Kindlin-2, and the effects of Kindlin-2 deletion on uterine development and reproduction capacity of female mice were observed. High expression and knockdown of Kindlin-2 in endometrial cancer cell lines HEC-1 and Ish were used to detect the regulation of mammalian target of rapamycin (mTOR) signaling pathway. In addition, uterine proteins of the female mice with specific knockout of Kindlin-2 and female mice in the control group were extracted to detect the protein levels of key molecules of mTOR signaling pathway and Hippo signaling pathway.

RESULTS

The mouse model of uterine specific knockout of Kindlin-2 was successfully constructed. The knockout efficiency of Kindlin-2 in mouse uterus was identified and verified by mouse tail polymerase chain reaction (PCR), Western blot protein identification, immunohistochemical staining (IHC) and other methods. Compared with the control group, the female mice with uterus specific deletion of Kindlin-2 lost weight, seriously impaired reproductive ability, and the number of newborn mice decreased, but the proportion of the female mice and male mice in the newborn mice did not change. Hematoxylin eosin staining (HE) experiment showed that the endometrium of Kindlin-2 knockout group was incomplete and the thickness of uterine wall became thinner. In terms of mechanism, the deletion of Kindlin-2 in endo-metrial cancer cell lines HEC-1 and Ish could downregulate the protein levels of mTOR, phosphorylated mTOR, adenosine monophosphate-activated protein kinase (AMPK), phosphorylated AMPK and phosphorylated ribosomal protein S6 (S6), and the mTOR signal pathway was inhibited. It was found that the specific deletion of Kindlin-2 could upregulate the protein levels of Mps one binding 1 (MOB1) and phosphorylated Yes-associated protein (YAP) in the uterus of the female mice, and the Hippo signal pathway was activated.

CONCLUSION

Kindlin-2 inhibits the development of uterus by inhibiting mTOR signal pathway and activating Hippo signal pathway, thereby inhibiting the fertility of female mice.

Kindlin2 regulates neural crest specification via integrin-independent regulation of the FGF signaling pathway

The focal adhesion protein Kindlin2 is essential for integrin activation, a process that is fundamental to cell-extracellular matrix adhesion. Kindlin 2 (Fermt2) is widely expressed in mouse embryos, and its absence causes lethality at the peri-implantation stage due to the failure to trigger integrin activation. The function of kindlin2 during embryogenesis has not yet been fully elucidated as a result of this early embryonic lethality. Here, we showed that kindlin2 is essential for neural crest (NC) formation in Xenopus embryos. Loss-of-function assays performed with kindlin2-specific morpholino antisense oligos (MOs) or with CRISPR/Cas9 techniques in Xenopus embryos severely inhibit the specification of the NC. Moreover, integrin-binding-deficient mutants of Kindlin2 rescued the phenotype caused by loss of kindlin2, suggesting that the function of kindlin2 during NC specification is independent of integrins. Mechanistically, we found that Kindlin2 regulates the fibroblast growth factor (FGF) pathway, and promotes the stability of FGF receptor 1. Our study reveals a novel function of Kindlin2 in regulating the FGF signaling pathway and provides mechanistic insights into the function of Kindlin2 during NC specification.

Kindlins: Roles in development and cancer progression

The Kindlins are FERM domain proteins comprising three members (Kindlin-1, -2 and -3) which are evolutionarily conserved. Kindlins bind with β-integrin cytoplasmic tails and execute broad biological functions including directed cell migration, proliferation, differentiation and survival. In light of more and more evidence point to the importance of Kindlin family members in normal development and human diseases especially in cancers, we aim to portrait the profile of Kindlins in the regulation of embryonic development and cancer progression. We first summarize all the known binding proteins for individual member of Kindlin family. We then outline the Kindlin-regulated signaling pathways including Wnt/β-catenin, TGFβ, EGFR, and Hedgehog signalings. Furthermore, we descript the pivotal role of Kindlins in embryonic development in detail with notions that Kindlin-1 is highly expressed in endo/ectodermal originated tissues, Kindlin-2 is highly expressed in mesoderm-derived tissues and Kindlin-3 is highly expressed in mesoderm- and ectoderm-derived tissues. Deregulation of Kindlins is generally reported in cancers from different organs. We also briefly descript the role of Kindlins in other diseases. Finally, we update the recent understanding of how Kindlins are regulated and modified as well as the degradation mechanism of Kindlins, respectively.

Kindlin-2 directly binds actin and regulates integrin outside-in signaling

Bledzka et al. show that kindlin-2 binds actin via its F0 domain, and mutation of this site diminishes cell spreading, revealing a new mechanism by which kindlin-2 regulates cellular responses.

Reduced levels of kindlin-2 (K2) in endothelial cells derived from K2^+/− mice or C2C12 myoblastoid cells treated with K2 siRNA showed disorganization of their actin cytoskeleton and decreased spreading. These marked changes led us to examine direct binding between K2 and actin. Purified K2 interacts with F-actin in cosedimentation and surface plasmon resonance analyses and induces actin aggregation. We further find that the F0 domain of K2 binds actin. A mutation, LK⁴⁷/AA, within a predicted actin binding site (ABS) of F0 diminishes its interaction with actin by approximately fivefold. Wild-type K2 and K2 bearing the LK⁴⁷/AA mutation were equivalent in their ability to coactivate integrin αIIbβ3 in a CHO cell system when coexpressed with talin. However, K2-LK⁴⁷/AA exhibited a diminished ability to support cell spreading and actin organization compared with wild-type K2. The presence of an ABS in F0 of K2 that influences outside-in signaling across integrins establishes a new foundation for considering how kindlins might regulate cellular responses.

Ptbp1 and Exosc9 knockdowns trigger skin stability defects through different pathways

In humans, genetic diseases affecting skin integrity (genodermatoses) are generally caused by mutations in a small number of genes that encode structural components of the dermal-epidermal junctions. In this article, we first show that inactivation of both exosc9, which encodes a component of the RNA exosome, and ptbp1, which encodes an RNA-binding protein abundant in Xenopus embryonic skin, impairs embryonic Xenopus skin development, with the appearance of dorsal blisters along the anterior part of the fin. However, histological and electron microscopy analyses revealed that the two phenotypes are distinct. Exosc9 morphants are characterized by an increase in the apical surface of the goblet cells, loss of adhesion between the sensorial and peridermal layers, and a decrease in the number of ciliated cells within the blisters. Ptbp1 morphants are characterized by an altered goblet cell morphology. Gene expression profiling by deep RNA sequencing showed that the expression of epidermal and genodermatosis-related genes is also differentially affected in the two morphants, indicating that alterations in post-transcriptional regulations can lead to skin developmental defects through different routes. Therefore, the developing larval epidermis of Xenopus will prove to be a useful model for dissecting the post-transcriptional regulatory network involved in skin development and stability with significant implications for human diseases.