Combinatorial effects of Flk1 and Tal1 on vascular and hematopoietic development in the mouse

Mouse embryos mutant for the VEGF receptor, VEGFR2, Flk-1, or Kdr, fail to form both endothelial and hematopoietic cells, suggesting a possible role in a common progenitor to both lineages. The transcription factor Tal1 (Scl), is not expressed in Flk1(−/−) embryos, consistent with a downstream role in the Flk1 pathway. We tested whether expression of Tal1 under the Flk1 promoter was sufficient to rescue the loss of endothelial and hematopoietic cells in Flk1 mutants. Only partial rescue of hematopoiesis and endothelial development was observed in vivo. However, Flk1(−/Tal1) embryonic stem (ES) cells were capable of blast colony formation in vitro at levels equivalent to Flk1(+/−) heterozygotes. Ectopic expression of Tal1 under the Flk1 promoter in Flk1(+/−) mouse embryos or ES cells caused no obvious pathology but increased the number of blast colony forming cells (BL-CFCs) and enhanced their hematopoietic potential. These single-cell-derived BL-CFCs also produced smooth muscle cells in vitro. Increased Tal1 expression inhibited smooth muscle differentiation in this assay, whereas loss of Tal1 promoted smooth muscle formation. We propose a model in which the combinatorial effects of Flk1 and Tal1 act to regulate cell fate choice in early development into hematopoietic, endothelial, and smooth muscle lineages

Functional Response Properties of VIP-expressing Inhibitory Neurons in Mouse Visual and Auditory Cortex

Despite accounting for about 20% of all the layer 2/3 inhibitory interneurons, the vasoactive intestinal polypeptide (VIP) expressing neurons remain the least thoroughly studied of the major inhibitory subtypes. In recent studies, VIP neurons have been shown to be activated by a variety of cortico-cortical and neuromodulatory inputs, but their basic sensory response properties remain poorly characterized. We set out to explore the functional properties of layer 2/3 VIP neurons in the primary visual (V1) and primary auditory cortex (A1), using two-photon imaging guided patch recordings. We found that in the V1, VIP neurons were generally broadly tuned, with their sensory response properties resembling those of parvalbumin (PV) expressing neurons. With the exception of response latency, they did not exhibit a significant difference from PV neurons across any of the properties tested, including overlap index, response modulation, orientation selectivity and direction selectivity. In the A1, on the other hand, VIP neurons had a strong tendency to be intensity selective, which is a property associated with a subset of putative pyramidal cells and virtually absent in PV neurons. VIP neurons had a best intensity that was significantly lower than that of PV and putative pyramidal neurons.Finally, sensory evoked spike responses of VIP neurons were delayed relative to pyramidal and PV neurons in both the V1 and A1. Combined, these results demonstrate that the sensory response properties of VIP neurons do not fit a simple model of being either PV-like broadly tuned or pyramidal-like narrowly tuned. Instead, the selectivity pattern varies with sensory area and can even be, as in the case of low sound intensity responsiveness, distinct from both PV and pyramidal neurons

Survival and Growth of Epiphytic Ferns Depend on Resource Sharing

Locally available resources can be shared within clonal plant systems through physiological integration, thus enhancing their survival and growth. Most epiphytes exhibit clonal growth habit, but few studies have tested effects of physiological integration (resource sharing) on survival and growth of epiphytes and whether such effects vary with species. We conducted two experiments, one on individuals (single ramets) and another on groups (several ramets within a plot), with severed and intact rhizome treatments (without and with physiological integration) on two dominant epiphytic ferns (Polypodiodes subamoena and Lepisorus scolopendrium) in a subtropical montane moist forest in Southwest China. Rhizome severing (preventing integration) significantly reduced ramet survival in the individual experiment and number of surviving ramets in the group experiment, and it also decreased biomass of both species in both experiments. However, the magnitude of such integration effects did not vary significantly between the two species. We conclude that resource sharing may be a general strategy for clonal epiphytes to adapt to forest canopies where resources are limited and heterogeneously distributed in space and time