Distinct apical and basolateral mechanisms drive planar cell polarity-dependent convergent extension of the mouse neural plate.

The mechanisms of tissue convergence and extension (CE) driving axial elongation in mammalian embryos, and in particular, the cellular behaviors underlying CE in the epithelial neural tissue, have not been identified. Here we show that mouse neural cells undergo mediolaterally biased cell intercalation and exhibit both apical boundary rearrangement and polarized basolateral protrusive activity. Planar polarization and coordination of these two cell behaviors are essential for neural CE, as shown by failure of mediolateral intercalation in embryos mutant for two proteins associated with planar cell polarity signaling: Vangl2 and Ptk7. Embryos with mutations in Ptk7 fail to polarize cell behaviors within the plane of the tissue, whereas Vangl2 mutant embryos maintain tissue polarity and basal protrusive activity but are deficient in apical neighbor exchange. Neuroepithelial cells in both mutants fail to apically constrict, leading to craniorachischisis. These results reveal a cooperative mechanism for cell rearrangement during epithelial morphogenesis.

Tgif1 and Tgif2 regulate Nodal signaling and are required for gastrulation.

Tgif1 and Tgif2 are transcriptional co-repressors that limit the response to TGFbeta signaling and play a role in regulating retinoic-acid-mediated gene expression. Mutations in human TGIF1 are associated with holoprosencephaly, but it is unclear whether this is a result of deregulation of TGFbeta/Nodal signaling, or of effects on other pathways. Surprisingly, mutation of Tgif1 in mice results in only relatively mild developmental phenotypes in most strain backgrounds. Here, we show that loss-of-function mutations in both Tgif1 and Tgif2 result in a failure of gastrulation. By conditionally deleting Tgif1 in the epiblast, we demonstrate that a single wild-type allele of Tgif1 in the extra-embryonic tissue allows the double null embryos to gastrulate and begin organogenesis, suggesting that extra-embryonic Tgif function is required for patterning the epiblast. Genetically reducing the dose of Nodal in embryos lacking all Tgif function results in partial rescue of the gastrulation defects. Conditional double null embryos have defects in left-right asymmetry, which are also alleviated by reducing the dose of Nodal. Together, these data show that Tgif function is required for gastrulation, and provide the first clear evidence that Tgifs limit the transcriptional response to Nodal signaling during early embryogenesis.

A comparison of three NMDA receptor antagonists in the treatment of prolonged status epilepticus.

Three different classes of NMDA receptor antagonists were compared for their effectiveness in terminating prolonged status epilepticus (SE), induced by continuous hippocampal stimulation. Animals were treated after 150 min of SE by intraperitoneal administration of increasing doses of 3-((R,S)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP), MK-801 (dizocilpine), ifenprodil, or saline. EEG recordings were used to determine seizure termination. The first experiment (n = 57 animals) determined the most effective anticonvulsant dose of each agent by determining its ability to terminate SE within the next 300 min. Five control rats treated with normal saline after 150 min of SE continued to exhibit continuous seizures for the next 300 min. All drugs were administered after 150 min of SE. CPP terminated seizures with an ED(50) of 6.4 mg/kg; the maximal effective dose was 15 mg/kg. MK-801 has an ED(50) of 1.4 mg/kg; the maximal effective dose was 2 mg/kg. Ifenprodil was maximally effective at 30 mg/kg. However, an ED(50) could not be calculated. In a subsequent experiment, the NMDA antagonists were compared for their ability to terminate prolonged SE within 60 min of their administration at the most effective dose. MK-801 (2.0 mg/kg) terminated SE in 6 of 10 animals within 60 min, CPP (15 mg/kg) terminated it in 1 of 9 animals; ifenprodil (30 mg/kg) did not terminate it in any of 9 animals treated. In the 300 min following administration, CPP (6/9) and MK-801 (6/10) were equally efficacious in terminating SE but ifenprodil (2/7) was less effective (P = 0.065, chi-square test). The results indicate that the non-competitive NMDA receptor antagonist MK-801 was superior to the competitive antagonist CPP and the pH-sensitive site antagonist ifenprodil, in terminating prolonged experimental SE.