Expression and molecular diversity of Tcf7l2 in the developing murine cerebellum and brain.

The Wingless family of secreted proteins impinges on multiple aspects of vertebrate nervous system development, from early global patterning and cell fate decision to synaptogenesis. Here, we mapped the developmental expression of the Tcf7l2, which is key to the canonical Wingless signaling cascade, in the developing cerebellum. The exclusive and transient expression of Tcf7l2 in ventricular and Olig2-defined precursor cells within the cerebellar anlage, and its predominant expression in postmitotic neurons in the midbrain/inferior colliculus allowed us to ask whether cell type-specific differences are also reflected in splice isoform variability. We also included in this analysis intestinal epithelia, where Tcf7l2 function has been intensively studied. Our data reveal extensive variability of Tcf7l2 splicing in the central nervous system. Additional variability in brain-expressed Tcf7l2 is generated by a length polymorphism of expressed mRNAs in a stretch of normally nine adenines found at the beginning of exon 18, reminiscent of variability observed at the same site in cancers with microsatellite instability. A consensus emerging from our data is that the expression of isoforms comprising or lacking the C-clamp motif, which has been linked by in vitro studies to the regulation of cell growth, is indeed tightly correlated with the proliferative status in vivo.

Developmental expression and differentiation-related neuron-specific splicing of metastasis suppressor 1 (Mtss1) in normal and transformed cerebellar cells.

BACKGROUND: Mtss1 encodes an actin-binding protein, dysregulated in a variety of tumors, that interacts with sonic hedgehog/Gli signaling in epidermal cells. Given the prime importance of this pathway for cerebellar development and tumorigenesis, we assessed expression of Mtss1 in the developing murine cerebellum and human medulloblastoma specimens. RESULTS: During development, Mtss1 is transiently expressed in granule cells, from the time point they cease to proliferate to their synaptic integration. It is also expressed by granule cell precursor-derived medulloblastomas. In the adult CNS, Mtss1 is found exclusively in cerebellar Purkinje cells. Neuronal differentiation is accompanied by a switch in Mtss1 splicing. Whereas immature granule cells express a Mtss1 variant observed also in peripheral tissues and comprising exon 12, this exon is replaced by a CNS-specific exon, 12a, in more mature granule cells and in adult Purkinje cells. Bioinformatic analysis of Mtss1 suggests that differential exon usage may affect interaction with Fyn and Src, two tyrosine kinases previously recognized as critical for cerebellar cell migration and histogenesis. Further, this approach led to the identification of two evolutionary conserved nuclear localization sequences. These overlap with the actin filament binding site of Mtss1, and one also harbors a potential PKA and PKC phosphorylation site. CONCLUSION: Both the pattern of expression and splicing of Mtss1 is developmentally regulated in the murine cerebellum. These findings are discussed with a view on the potential role of Mtss1 for cytoskeletal dynamics in developing and mature cerebellar neurons.

Developmental increase of total cell numbers in the murine cerebellum.

The cerebellum has been widely used as a paradigm to study basic mechanisms of brain development and cortical histogenesis. Its highly regular structure has always made it particularly attractive to approaches relying on, and yielding, quantitative information, which provide a cornerstone of systems-oriented integrative analyses. Astonishingly, though, a systematic quantification of cell generation during cerebellar development has so far not been provided. Here, we use the isotropic fractionator (i.e., cell counts based on tissue homogenates from anatomically defined regions; cf. Herculano-Houzel S, Lent R., J Neurosci. 2005;25:2518-21) to assess the developmental increase of total cell numbers in the murine cerebellum from embryonic day 17 into early adulthood. Our data show that the quantitative increase of cerebellar cell numbers follows a classical, S-shaped growth curve as described by the Hill-equation. The adult murine cerebellum was found to comprise a total of (44.03+/-0.42) * 10(6) cells, half of which are generated before postnatal day 12+/-0.18. Consistent results were obtained by using two approaches to cell counting, one based on manual assessment, the other on flow cytometry. These data provide a reliable quantitative description of cerebellar growth in the mouse and define a predictive model that should allow their integration with quantitative and qualitative descriptions of cerebellar development.