Emx1 and Emx2 cooperate in initial phase of archipallium development

Emx1 and Emx2 are mouse cognates of the Drosophila head gap gene, ems. Previously we have reported that the dentate gyrus is affected in Emx2 single mutants, and defects are subtle in Emx1 single mutants. In most of the cortical region Emx1 and Emx2 functions would be redundant. To test this assumption here we examined the Emx1 and Emx2 double mutant phenotype. In the double mutants the archipallium was transformed into the roof without establishing the signaling center at the cortical hem and without developing the choroid plexus. We propose that Emx1 and Emx2 cooperate in generation of the boundary between the roof and archipallium; these genes develop the archipallium against the roof. This process probably occurs immediately after the neural tube closure concomitant with the Emx1 expression.     

Emx2 and early hair cell development in the mouse inner ear

Emx2 is a homeodomain protein that plays a critical role in inner ear development. Homozygous null mice die at birth with a range of defects in the CNS, renal system and skeleton. The cochlea is shorter than normal with about 60% fewer auditory hair cells. It appears to lack outer hair cells and some supporting cells are either absent or fail to differentiate. Many of the hair cells differentiate in pairs and although their hair bundles develop normally their planar cell polarity is compromised. Measurements of cell polarity suggest that classic planar cell polarity molecules are not directly influenced by Emx2 and that polarity is compromised by developmental defects in the sensory precursor population or by defects in epithelial cues for cell alignment. Planar cell polarity is normal in the vestibular epithelia although polarity reversal across the striola is absent in both the utricular and saccular maculae. In contrast, cochlear hair cell polarity is disorganized. The expression domain for Bmp4 is expanded and Fgfr1 and Prox1 are expressed in fewer cells in the cochlear sensory epithelium of Emx2 null mice. We conclude that Emx2 regulates early developmental events that balance cell proliferation and differentiation in the sensory precursor population.     

Development of midline cell types and commissural axon tracts requires Fgfr1 in the cerebrum

The adult cerebral hemispheres are connected to each other by specialized midline cell types and by three axonal tracts: the corpus callosum, the hippocampal commissure, and the anterior commissure. Many steps are required for these tracts to form, including early patterning and later axon pathfinding steps. Here, the requirement for FGF signaling in forming midline cell types and commissural axon tracts of the cerebral hemispheres is examined. Fgfr1, but not Fgfr3, is found to be essential for establishing all three commissural tracts. In an Fgfr1 mutant, commissural neurons are present and initially project their axons, but these fail to cross the midline that separates the hemispheres. Moreover, midline patterning defects are observed in the mutant. These defects include the loss of the septum and three specialized glial cell types, the indusium griseum glia, midline zipper glia, and glial wedge. Our findings demonstrate that FGF signaling is required for generating telencephalic midline structures, in particular septal and glial cell types and all three cerebral commissures. In addition, analysis of the Fgfr1 heterozygous mutant, in which midline patterning is normal but commissural defects still occur, suggests that at least two distinct FGF-dependent mechanisms underlie the formation of the cerebral commissures.     

The expression pattern of Follistatin-like 1 in mouse central nervous system development

Follistatin-like 1 (Fstl1), also named TSC-36 (TGF-β-stimulated clone 36), was first cloned from the mouse osteoblastic MC3T3-E1 cell line and can be up-regulated by TGF-β. To better study the function of Fstl1 during the development of the mouse central nervous system (CNS), we examined Fstl1 expression in the developing mouse CNS, in detail, by in situ hybridization. Our results show that Fstl1 is strongly expressed in the telencephalon, diencephalon, brainstem, limbic system and spinal cord. In the telencephalon, Fstl1 positive cells are mainly located in the ventricular zone (VZ) and the subventricular zone (SVZ); a relatively weak signal was observed in layers II and III of the neocortex at postnatal stages. Fstl1 expression is robust in the developing hippocampus and persists to P20. In the developing diencephalon and hindbrain, abundant Fstl1 signals were also detected in nuclei including the medial habenular nucleus, the medial dorsal nucleus, the cochlear nuclei and so on. In addition, a strong expression of Fstl1 was detected in the thalamencephalic signal center, as well as in the olfactory cortex from E14.5 to P0. Meanwhile, Fstl1 was expressed in the septal area and the cingulate gyrus of the limbic system after birth. A high level of expression was also observed in the ventral horn of the spinal cord. These results indicate that Fstl1 may play an important role during CNS development in the mouse.     

Carnosine uptake in rat choroid plexus primary cell cultures and choroid plexus whole tissue from PEPT2 null mice

PEPT2 is functionally active and localized to the apical membrane of rat choroid plexus epithelial cells. However, little is known about the transport mechanisms of endogenous neuropeptides in choroid plexus, and the role of PEPT2 in this process. In the present study, we examined the uptake kinetics of carnosine in rat choroid plexus primary cell cultures and choroid plexus whole tissue from wild-type (PEPT2(+/+)) and null (PEPT2(-/-)) mice. Our results indicate that carnosine is preferentially taken up from the apical as opposed to basolateral membrane of cell monolayers, and that basolateral efflux in limited. Transepithelial flux of carnosine was not distinguishable from that of paracellular diffusion. The apical uptake of carnosine was characterized by a high affinity (K(m) = 34 microM), low capacity (V(max) = 73 pmol/mg protein/min) process, consistent with that of PEPT2. The non-saturable component was small (K(d) = 0.063 microL/mg protein/min) and, under linear conditions, was only 3% of the total uptake. Studies in transgenic mice clearly demonstrated that PEPT2 was responsible for over 90% of carnosine's uptake in choroid plexus whole tissue. These findings elucidate the unique role of PEPT2 in regulating neuropeptide homeostasis at the blood-cerebrospinal fluid interface.     

Conserved roles of ems/Emx and otd/Otx genes in olfactory and visual system development in Drosophila and mouse

The regional specialization of brain function has been well documented in the mouse and fruitfly. The expression of regulatory factors in specific regions of the brain during development suggests that they function to establish or maintain this specialization. Here, we focus on two such factors—the Drosophila cephalic gap genes empty spiracles (ems) and orthodenticle (otd), and their vertebrate homologues Emx1/2 and Otx1/2—and review novel insight into their multiple crucial roles in the formation of complex sensory systems. While the early requirement of these genes in specification of the neuroectoderm has been discussed previously, here we consider more recent studies that elucidate the later functions of these genes in sensory system formation in vertebrates and invertebrates. These new studies show that the ems and Emx genes in both flies and mice are essential for the development of the peripheral and central neurons of their respective olfactory systems. Moreover, they demonstrate that the otd and Otx genes in both flies and mice are essential for the development of the peripheral and central neurons of their respective visual systems. Based on these recent experimental findings, we discuss the possibility that the olfactory and visual systems of flies and mice share a common evolutionary origin, in that the conserved visual and olfactory circuit elements derive from conserved domains of otd/Otx and ems/Emx action in the urbilaterian ancestor.     

The S. cerevisiae Yap1 and Yap2 transcription factors share a common cadmium-sensing domain

Towards elucidating the function of Yap2, which remains unclear, we have taken advantage of the C-terminal homology between Yap1 and Yap2. Swapping domains experiments show that the Yap2 C-terminal domain functionally substitutes for the homologous Yap1 domain in the response to Cd, but not to H2O2. We conclude that specificity determinants of the Cd response are encoded within both Yap1 and Yap2 C-terminus, whereas those required for H2O2 response are only present in the Yap1 C-terminus. Furthermore, our results identify FRM2 as Cd-responsive Yap2 target and indicate a possible role of this protein in regulating a metal stress response.     

The E protein-TCF1 axis controls γδ T cell development and effector fate

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NFBD1/MDC1 stabilizes oncogenic MDM2 to contribute to cell fate determination in response to DNA damage

In response to DNA damage, NFBD1/MDC1 induces the accumulation of DNA repair machinery such as MRN complex at the sites of damaged DNA to form nuclear foci. In this study, we found that NFBD1 directly interacts with MDM2 and increases its stability. During adriamycin (ADR)-mediated apoptosis, expression levels of NFBD1 reduced in association with the down-regulation of MDM2. Enforced expression of NFBD1 resulted in a significant stabilization of MDM2. Consistent with these observations, siRNA-mediated knockdown of the endogenous NFBD1 decreased the amounts of the endogenous MDM2. Immunoprecipitation and in vitro pull-down assays demonstrated that NFBD1 interacts with MDM2 through its COOH-terminal BRCT domains. In accordance with our recent results, enforced expression of NFBD1 rendered cells resistant to DNA damage. Similar results were also obtained in cells expressing exogenous MDM2. Taken together, our present findings suggest that NFBD1-mediated stabilization contributes to cell survival in response to DNA damage.