VIP blockade leads to microcephaly in mice via disruption of Mcph1-Chk1 signaling.

Autosomal recessive primary microcephaly (MCPH) is a genetic disorder that causes a reduction of cortical outgrowth without severe interference with cortical patterning. It is associated with mutations in a number of genes encoding protein involved in mitotic spindle formation and centrosomal activities or cell cycle control. We have shown previously that blocking vasoactive intestinal peptide (VIP) during gestation in mice by using a VIP antagonist (VA) results in microcephaly. Here, we have shown that the cortical abnormalities caused by prenatal VA administration mimic the phenotype described in MCPH patients and that VIP blockade during neurogenesis specifically disrupts Mcph1 signaling. VA administration reduced neuroepithelial progenitor proliferation by increasing cell cycle length and promoting cell cycle exit and premature neuronal differentiation. Quantitative RT-PCR and Western blot showed that VA downregulated Mcph1. Inhibition of Mcph1 expression led to downregulation of Chk1 and reduction of Chk1 kinase activity. The inhibition of Mcph1 and Chk1 affected the expression of a specific subset of cell cycle–controlling genes and turned off neural stem cell proliferation in neurospheres. Furthermore, in vitro silencing of either Mcph1 or Chk1 in neurospheres mimicked VA-induced inhibition of cell proliferation. These results demonstrate that VIP blockade induces microcephaly through Mcph1 signaling and suggest that VIP/Mcph1/Chk1 signaling is key for normal cortical development.journal articleresearch support, non-u.s. gov't2011 Augimporte

Placental lactogens induce serotonin biosynthesis in a subset of mouse beta cells during pregnancy

AIMS/HYPOTHESIS: Upregulation of the functional beta cell mass is required to match the physiological demands of mother and fetus during pregnancy. This increase is dependent on placental lactogens (PLs) and prolactin receptors, but the mechanisms underlying these events are only partially understood. We studied the mRNA expression profile of mouse islets during pregnancy to gain a better insight into these changes. METHODS: RNA expression was measured ex vivo via microarrays and quantitative RT-PCR. In vivo observations were extended by in vitro models in which ovine PL was added to cultured mouse islets and MIN6 cells. RESULTS: mRNA encoding both isoforms of the rate-limiting enzyme of serotonin biosynthesis, tryptophan hydroxylase (TPH), i.e. Tph1 and Tph2, were strongly induced (fold change 25- to 200-fold) during pregnancy. This induction was mimicked by exposing islets or MIN6 cells to ovine PLs for 24 h and was dependent on janus kinase 2 and signal transducer and activator of transcription 5. Parallel to Tph1 mRNA and protein induction, islet serotonin content increased to a peak level that was 200-fold higher than basal. Interestingly, only a subpopulation of the beta cells was serotonin-positive in vitro and in vivo. The stored serotonin pool in pregnant islets and PL-treated MIN6 cells was rapidly released (turnover once every 2 h). CONCLUSIONS/INTERPRETATION: A very strong lactogen-dependent upregulation of serotonin biosynthesis occurs in a subpopulation of mouse islet beta cells during pregnancy. Since the newly formed serotonin is rapidly released, this lactogen-induced beta cell function may serve local or endocrine tasks, the nature of which remains to be identified

Time-Resolved Observation of Luminescence from a Charge-Transfer State in Double Quantum Wells

We have directly observed the buildup of a charge-transfer state in double quantum well structures due to electron and hole tunneling in opposite directions.</jats:p