Differentiated cells assume complex shapes through polarized cell migration and growth. These processes require the restricted organization of the actin cytoskeleton at limited subcellular regions. IKK epsilon is a member of the IkappaB kinase family, and its developmental role has not been clear. Drosophila IKK epsilon was localized to the ruffling membrane of cultured cells and was required for F actin turnover at the cell margin. In IKK epsilon mutants, tracheal terminal cells, bristles, and arista laterals, which require accurate F actin assembly for their polarized elongation, all exhibited aberrantly branched morphology. These phenotypes were sensitive to a change in the dosage of Drosophila inhibitor of apoptosis protein 1 (DIAP1) and the caspase DRONC without apparent change in cell viability. In contrast to this, hyperactivation of IKK epsilon destabilized F actin-based structures. Expression of a dominant-negative form of IKK epsilon increased the amount of DIAP1. The results suggest that at the physiological level, IKK epsilon acts as a negative regulator of F actin assembly and maintains the fidelity of polarized elongation during cell morphogenesis. This IKK epsilon function involves the negative regulation of the nonapoptotic activity of DIAP1.

Summary Nedd4-1 is a ‘Neuronal Precursor Cell Expressed and Developmentally Downregulated Protein’ and among the most abundant E3 ubiquitin ligases in mammalian neurons. In analyses of conventional and conditional Nedd4-1 deficient mice, we found that Nedd4-1 plays a critical role in dendrite formation. Nedd4-1, the serine/threonine kinase TNIK, and Rap2A form a complex that controls Nedd4-1-mediated ubiquitination of Rap2A. Ubiquitination by Nedd4-1 inhibits Rap2A function, which reduces the activity of Rap2 effector kinases of the TNIK family and promotes dendrite growth. We conclude that a Nedd4-1/Rap2A/TNIK signaling pathway regulates neurite growth and arborization in mammalian neurons.

Epithelial folding is typically driven by localized actomyosin contractility. However, it remains unclear how epithelia deform when myosin levels are low and uniform. In the Drosophila gastrula, dorsal fold formation occurs despite a lack of localized myosin changes, while the fold-initiating cells reduce cell height following basal shifts of polarity via an unknown mechanism. We show that cell shortening depends on an apical microtubule network organized by the CAMSAP protein Patronin. Prior to gastrulation, microtubule forces generated by the minus-end motor dynein scaffold the apical cell cortex into a dome-like shape, while the severing enzyme Katanin facilitates network remodelling to ensure tissue-wide cell size homeostasis. During fold initiation, Patronin redistributes following basal polarity shifts in the initiating cells, apparently weakening the scaffolding forces to allow dome descent. The homeostatic network that ensures size/shape homogeneity is thus repurposed for cell shortening, linking epithelial polarity to folding via a microtubule-based mechanical mechanism.

IKK-related kinases are key regulators of innate immunity and oncogenesis. While their effects on transcription are well characterized, their cytoplasmic functions remain poorly understood. Drosophila IKK-related kinase, IKKɛ, regulates cytoskeletal organization and cell elongation. Here, we demonstrate that IKKɛ is activated locally at the tip of growing mechanosensory bristles and regulates the rapid shuttling of recycling endosomes, independent of its roles in F-actin organization and caspase signaling. IKKɛ regulates the localization of recycling endosome regulators Rab11 and Dynein and phosphorylates their adaptor molecule, Nuclear fallout (Nuf). Nuf's negative regulation by IKKɛ suggests that local activation of IKKɛ inhibits Dynein on incoming recycling endosomes, converting them for outward transport. Mammalian IKK-related kinases also regulate the recycling endosomes' distribution by phosphorylating the Nuf homolog Rab11-FIP3. Our results establish an evolutionarily conserved function of IKK-related kinases in regulating recycling endosome dynamics and point to a key role of endosome dynamics in cell morphogenesis.

Highlights d Btd/Eve-dependent lateral MyoII shortens cells to initiate CF d Single-cell row Btd/Eve positional code accounts for only 80% of CF-initiating cells d Mis-specification arises due to MyoII noise, and yet the cells align among themselves d Mechanical coupling via planar polarized MyoII aligns cells to ensure CF linearity

Protein ubiquitination is a core regulatory determinant of neural development. Previous studies have indicated that the Nedd4-family E3 ubiquitin ligases Nedd4-1 and Nedd4-2 may ubiquitinate phosphatase and tensin homolog (PTEN) and thereby regulate axonal growth in neurons. Using conditional knockout mice, we show here that Nedd4-1 and Nedd4-2 are indeed required for axonal growth in murine central nervous system neurons. However, in contrast to previously published data, we demonstrate that PTEN is not a substrate of Nedd4-1 and Nedd4-2, and that aberrant PTEN ubiquitination is not involved in the impaired axon growth upon deletion of Nedd4-1 and Nedd4-2. Rather, PTEN limits Nedd4-1 protein levels by modulating the activity of mTORC1, a protein complex that controls protein synthesis and cell growth. Our data demonstrate that Nedd4-family E3 ligases promote axonal growth and branching in the developing mammalian brain, where PTEN is not a relevant substrate. Instead, PTEN controls neurite growth by regulating Nedd4-1 expression.

We have uncovered a functional bone morphogenetic protein (BMP) and activin system complete with ligands (BMP-6 and activin betaA/betaB), receptors (activin receptor-like kinase receptors 2, 3, and 4; activin type-II receptor; and BMP type-II receptor), and the binding protein follistatin in the human adrenocortical cell line H295R. Administration of activin and BMP-6 to cultures of H295R cells caused concentration-responsive increases in aldosterone production. The mRNA levels of steroidogenic acute regulatory protein or P450 steroid side-chain cleavage enzyme, the rate-limiting steps of adrenocortical steroidogenesis, were enhanced by activin and BMP-6. Activin and BMP-6 also activated the transcription of steroidogenic acute regulatory protein as well as the late-step steriodogenic enzyme CYP11B2. Activin enhanced ACTH-, forskolin-, or dibutyryl-cAMP- but not angiotensin II (Ang II)-induced aldosterone production, whereas BMP-6 specifically augmented Ang II-induced aldosterone production. Activin and ACTH but not BMP-6 increased cAMP production. Follistatin, which inhibits activin actions by binding, suppressed basal and ACTH-induced aldosterone secretion but failed to affect the Ang II-induced aldosterone level. Furthermore, MAPK signaling appeared to be involved in aldosterone production induced by Ang II and BMP-6 because an inhibitor of MAPK activation, U0126, reduced the level of aldosterone synthesis stimulated by Ang II and BMP-6 but not activin. In addition, Ang II reduced the expression levels of BMP-6 but increased that of activin betaB, whereas ACTH had no effect on these levels. Collectively, the present data suggest that activin acts to regulate adrenal aldosterone synthesis predominantly by modulating the ACTH-cAMP-protein kinase A signaling cascade, whereas BMP-6 works primarily by modulating the Ang II-MAPK cascade in human adrenal cortex in an autocrine/paracrine fashion.

In the present study, we investigated the cellular mechanism by which oocytes and bone morphogenetic proteins (BMPs) govern FSH-induced steroidogenesis using rat primary granulosa cells. BMP-6 and BMP-7 both inhibited FSH- and forskolin (FSK)-induced progesterone synthesis and reduced cAMP synthesis independent of the presence or absence of oocytes. BMP-7 also increased FSH-induced estradiol production, and the response was further augmented in the presence of oocytes. In contrast, BMP-6 had no impact on estradiol synthesis regardless of the presence of oocytes. Because BMP-7 changed neither FSK- nor cAMP-induced estradiol production, the BMP-7 action was mediated through a FSH receptor signaling mechanism that was independent of cAMP-protein kinase A pathway. Treatment with FSH but not cAMP activated ERK1/2 phosphorylation in granulosa cells, which was further accelerated by oocytes. A specific ERK inhibitor, U0126, increased estradiol production and decreased FSH- and FSK-induced progesterone production and cAMP synthesis. This suggests that ERK activation is directly linked to inhibition of estradiol synthesis and amplification of cAMP. Moreover, FSH-induced ERK1/2 phosphorylation was inhibited by BMP-7 but not influenced by BMP-6. In contrast, BMP signaling including Smad1/5/8 phosphorylation and Id-1 transcription was up-regulated by FSH and oocytes in granulosa cells through inhibition of Smad6/7 expression. Collectively, oocytes enhance FSH-induced MAPK activation and BMP signaling in granulosa cells, which leads to differential regulation of steroidogenesis elicited by BMPs in the presence of FSH in developing follicles.