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Abstract Background The mammalian thalamus relays sensory information from the periphery to the cerebral cortex for cognitive processing via the thalamocortical tract. The thalamocortical tract forms during embryonic development controlled by mechanisms that are not fully understood. β-catenin is a nuclear and cytosolic protein that transduces signals from secreted signaling molecules to regulate both cell motility via the cytoskeleton and gene expression in the nucleus. In this study we tested whether β-catenin is likely to play a role in thalamocortical connectivity by examining its expression and activity in developing thalamic neurons and their axons. Results At embryonic day (E)15.5, the time when thalamocortical axonal projections are forming, we found that the thalamus is a site of particularly high β-catenin mRNA and protein expression. As well as being expressed at high levels in thalamic cell bodies, β-catenin protein is enriched in the axons and growth cones of thalamic axons and its growth cone concentration is sensitive to Netrin-1. Using mice carrying the β-catenin reporter BAT-gal we find high levels of reporter activity in the thalamus. Further, Netrin-1 induces BAT-gal reporter expression and upregulates levels of endogenous transcripts encoding β-actin and L1 proteins in cultured thalamic cells. We found that β-catenin mRNA is enriched in thalamic axons and its 3'UTR is phylogenetically conserved and is able to direct heterologous mRNAs along the thalamic axon, where they can be translated. Conclusion We provide evidence that β-catenin protein is likely to be an important player in thalamocortcial development. It is abundant both in the nucleus and in the growth cones of post-mitotic thalamic cells during the development of thalamocortical connectivity and β-catenin mRNA is targeted to thalamic axons and growth cones where it could potentially be translated. β-catenin is involved in transducing the Netrin-1 signal to thalamic cells suggesting a mechanism by which Netrin-1 guides thalamocortical development.

Abstract Background Embryonic stem (ES) cells can differentiate into all cell types and have been used extensively to study factors affecting neuronal differentiation. ES cells containing mutations in known genes have the potential to provide useful in vitro models for the study of gene function during neuronal differentiation. Recently, mouse ES cell lines lacking the neurogenic transcription factor Pax6 were reported; neurons derived from these Pax6-/- ES cells died rapidly after neuronal differentiation in vitro. Results Here we report the derivation of new lines of Pax6-/- ES cells and the assessment of their ability to survive and differentiate both in vitro and in vivo. Neurons derived from our new Pax6-/- lines were viable and continued to elaborate processes in culture under conditions that resulted in the death of neurons derived from previously reported Pax6-/- ES cell lines. The new lines of Pax6-/-ES cells showed reduced neurogenic potential, mimicking the effects of loss of Pax6 in vivo. We used our new lines to generate Pax6-/- ↔ Pax6+/+ chimeras in which the mutant cells survived and displayed the same phenotypes as Pax6-/- cells in Pax6-/- ↔ Pax6+/+ chimeras made by embryo aggregation. Conclusions We suggest that loss of Pax6 from ES cells reduces their neurogenic capacity but does not necessarily result in the death of derived neurons. We offer these new lines as additional tools for those interested in the generation of chimeras and the analysis of in vitro ES cell models of Pax6 function during neuronal differentiation, embryonic and postnatal development.

Background: Embryonic stem (ES) cells can differentiate into all cell types and have been used extensively to study factors affecting neuronal differentiation. ES cells containing mutations in known genes have the potential to provide useful in vitro models for the study of gene function during neuronal differentiation. Recently, mouse ES cell lines lacking the neurogenic transcription factor Pax6 were reported; neurons derived from these Pax6-/- ES cells died rapidly after neuronal differentiation in vitro. Results: Here we report the derivation of new lines of Pax6-/- ES cells and the assessment of their ability to survive and differentiate both in vitro and in vivo. Neurons derived from our new Pax6-/- lines were viable and continued to elaborate processes in culture under conditions that resulted in the death of neurons derived from previously reported Pax6-/- ES cell lines. The new lines of Pax6-/-ES cells showed reduced neurogenic potential, mimicking the effects of loss of Pax6 in vivo. We used our new lines to generate Pax6-/- ↔ Pax6+/+ chimeras in which the mutant cells survived and displayed the same phenotypes as Pax6-/- cells in Pax6-/- ↔ Pax6+/+ chimeras made by embryo aggregation. Conclusions: We suggest that loss of Pax6 from ES cells reduces their neurogenic capacity but does not necessarily result in the death of derived neurons. We offer these new lines as additional tools for those interested in the generation of chimeras and the analysis of in vitro ES cell models of Pax6 function during neuronal differentiation, embryonic and postnatal development. [ABSTRACT FROM AUTHOR]