These kinases are highly Palo Alto, California 94304 related in sequence, are rapidly activated following treatment with TNF or IL-1, and specifically phosphorylate the two critical serines of IB. In addition, catalyti-Summary cally inactive forms of IKK-␣ and IKK-␤ inhibit NF-B activation mediated by TNF and IL-1, suggesting that IB kinase-␣ and -␤ (IKK-␣ and IKK-␤), the catalytic IKK-␣ and -␤ are responsible for IB phosphorylation subunits of the IKK complex, phosphorylate IB proand subsequent NF-B activation. Recently, a third teins on specific serine residues, thus targeting IB component of the IKK complex, designated NEMO/ for degradation and activating the transcription factor IKK-␥, was identified by complementation cloning in NF-NF-B. To elucidate the in vivo function of IKK-␤, we B-unresponsive cells (Yamaoka et al., 1998) and by generated IKK-␤-deficient mice. The homozygous affinity purification using antibodies to IKK-␣ (Rothwarf mouse embryo dies at ‫5.41ف‬ days of gestation due et al., 1998). NEMO is a 47 kDa protein that interacts to liver degeneration and apoptosis. IKK-␤-deficient with IKK-␣ and IKK-␤. NEMO-deficient cells are unable embryonic fibroblasts have both reduced basal NF-B to activate NF-B in response to TNF, IL-1, or LPS. activity and impaired cytokine-induced NF-B activa-Furthermore, IKK complexes lacking NEMO cannot be tion. Similarly, basal and cytokine-inducible kinase acactivated to phosphorylate IB, indicating that NEMO tivities of the IKK complex are greatly reduced in IKKis an essential component of the IKK complex. ␤-deficient cells. These results indicate that IKK-␤ is NF-B-inducing kinase (NIK) and MEKK1 have been crucial for liver development and regulation of NF-B proposed to be upstream activators of IKKs (Malinin et activity and that IKK-␣ can only partially compensate al., 1997; Nemoto et al., 1998). NIK is a MEKK family for the loss of IKK-␤. member that binds to and activates both IKK-␣ and IKK-␤ when overexpressed (Regnier et al., 1997; Woronicz et al., 1997). In addition, NIK can phosphorylate

Embryonic stem cell–derived fibroblasts with genetic disruption of the Arp2/3 complex are unable to form lamellipodia or undergo sustained directional migration.

Neurogenesis requires the coordination of neural progenitor proliferation and differentiation with cell-cycle regulation. However, the mechanisms coordinating these distinct cellular activities are poorly understood. Here we demonstrate for the first time that a Cut-like homeodomain transcription factor family member, Cux2 (Cutl2), regulates cell-cycle progression and development of neural progenitors. Cux2 loss-of-function mouse mutants exhibit smaller spinal cords with deficits in neural progenitor development as well as in neuroblast and interneuron differentiation. These defects correlate with reduced cell-cycle progression of neural progenitors coupled with diminished Neurod and p27Kip1 activity. Conversely, in Cux2 gain-of-function transgenic mice, the spinal cord is enlarged in association with enhanced neuroblast formation and neuronal differentiation, particularly with respect to interneurons. Furthermore, Cux2 overexpression induces high levels of Neurod and p27 Kip1. Mechanistically, we discovered through chromatin immunoprecipitation assays that Cux2 binds both the Neurod and p27Kip1 promoters in vivo, indicating that these interactions are direct. Our results therefore show that Cux2 functions at multiple levels during spinal cord neurogenesis. Cux2 initially influences cell-cycle progression in neural progenitors but subsequently makes additional inputs through Neurod and p27 Kip1 to regulate neuroblast formation, cell-cycle exit and cell-fate determination. Thus our work defines novel roles for Cux2 as a transcription factor that integrates cell-cycle progression with neural progenitor development during spinal cord neurogenesis.

In mammalian species, detection of pheromone cues by the vomeronasal organ (VNO) at different concentrations can elicit distinct behavioral responses and endocrine changes. It is not well understood how concentration-dependent activation of the VNO impacts innate behaviors. In this study, we find that, when mice investigate the urogenital areas of a conspecific animal, the urinary pheromones can reach the VNO at a concentration of ϳ1% of that in urine. At this level, urinary pheromones elicit responses from a subset of cells that are tuned to sex-specific cues and provide unambiguous identification of the sex and strain of animals. In contrast, low concentrations of urine do not activate these cells. Strikingly, we find a population of neurons that is only activated by low concentrations of urine. The properties of these neurons are not found in neurons responding to putative single-compound pheromones. Additional analyses show that these neurons are masked by high-concentration pheromones. Thus, an antagonistic interaction in natural pheromones results in the activation of distinct populations of cells at different concentrations. The differential activation is likely to trigger different downstream circuitry and underlies the concentration-dependent pheromone perception.

Neural crest cells (NCC) comprise a multipotent, migratory stem cell and progenitor population that gives rise to numerous cell and tissue types within a developing embryo, including craniofacial bone and cartilage, neurons and glia of the peripheral nervous system, and melanocytes within the skin. Here we describe two novel stable transgenic mouse lines suitable for lineage tracing and analysis of gene function in NCC. Firstly, using the F10N enhancer of the Mef2c gene (Mef2c-F10N) linked to LacZ, we generated transgenic mice (Mef2c-F10N-LacZ) that express LacZ in the majority, if not all migrating NCC that delaminate from the neural tube. Mef2c-F10N-LacZ then continues to be expressed primarily in neurogenic, gliogenic and melanocytic NCC and their derivatives, but not in ectomesenchymal derivatives. Secondly, we used the same Mef2c-F10N enhancer together with Cre recombinase to generate transgenic mice (Mef2c-F10N-Cre) that can be used to indelibly label, or alter gene function in, migrating NCC and their derivatives. At early stages of development, Mef2c-F10N-LacZ and Mef2c-F10N-Cre label NCC in a pattern similar to Wnt1-Cre mice, with the exception that Mef2c-F10N-LacZ and Mef2c-F10N-Cre specifically label NCC that have delaminated from the neural plate, while premigratory NCC are not labeled. Thus, our Mef2c-F10N-LacZ and Mef2c-F10N-Cre transgenic mice provide new resources for tracing migratory NCC and analyzing gene function in migrating and differentiating NCC independently of NCC formation.