Mice carrying a hypomorphic Evi1 allele are embryonic viable but exhibit severe congenital heart defects.

The ecotropic viral integration site 1 (Evi1) oncogenic transcription factor is one of a number of alternative transcripts encoded by the Mds1 and Evi1 complex locus (Mecom). Overexpression of Evi1 has been observed in a number of myeloid disorders and is associated with poor patient survival. It is also amplified and/or overexpressed in many epithelial cancers including nasopharyngeal carcinoma, ovarian carcinoma, ependymomas, and lung and colorectal cancers. Two murine knockout models have also demonstrated Evi1's critical role in the maintenance of hematopoietic stem cell renewal with its absence resulting in the death of mutant embryos due to hematopoietic failure. Here we characterize a novel mouse model (designated Evi1(fl3)) in which Evi1 exon 3, which carries the ATG start, is flanked by loxP sites. Unexpectedly, we found that germline deletion of exon3 produces a hypomorphic allele due to the use of an alternative ATG start site located in exon 4, resulting in a minor Evi1 N-terminal truncation and a block in expression of the Mds1-Evi1 fusion transcript. Evi1(δex3/δex3) mutant embryos showed only a mild non-lethal hematopoietic phenotype and bone marrow failure was only observed in adult Vav-iCre/+, Evi1(fl3/fl3) mice in which exon 3 was specifically deleted in the hematopoietic system. Evi1(δex3/δex3) knockout pups are born in normal numbers but die during the perinatal period from congenital heart defects. Database searches identified 143 genes with similar mutant heart phenotypes as those observed in Evi1(δex3/δex3) mutant pups. Interestingly, 42 of these congenital heart defect genes contain known Evi1-binding sites, and expression of 18 of these genes are also effected by Evi1 siRNA knockdown. These results show a potential functional involvement of Evi1 target genes in heart development and indicate that Evi1 is part of a transcriptional program that regulates cardiac development in addition to the development of blood.

Goofy coordinates the acuity of olfactory signaling.

The basic scheme of odor perception and signaling from olfactory cilia to the brain is well understood. However, factors that affect olfactory acuity of an animal, the threshold sensitivity to odorants, are less well studied. Using signal sequence trap screening of a mouse olfactory epithelium cDNA library, we identified a novel molecule, Goofy, that is essential for olfactory acuity in mice. Goofy encodes an integral membrane protein with specific expression in the olfactory and vomeronasal sensory neurons and predominant localization to the Golgi compartment. Goofy-deficient mice display aberrant olfactory phenotypes, including the impaired trafficking of adenylyl cyclase III, stunted olfactory cilia, and a higher threshold for physiological and behavioral responses to odorants. In addition, the expression of dominant-negative form of cAMP-dependent protein kinase results in shortening of olfactory cilia, implying a possible mechanistic link between cAMP and ciliogenesis in the olfactory sensory neurons. These results demonstrate that Goofy plays an important role in establishing the acuity of olfactory sensory signaling.

Chromatin modification of Notch targets in olfactory receptor neuron diversification.

Neuronal-class diversification is central during neurogenesis. This requirement is exemplified in the olfactory system, which utilizes a large array of olfactory receptor neuron (ORN) classes. We discovered an epigenetic mechanism in which neuron diversity is maximized via locus-specific chromatin modifications that generate context-dependent responses from a single, generally used intracellular signal. Each ORN in Drosophila acquires one of three basic identities defined by the compound outcome of three iterated Notch signaling events during neurogenesis. Hamlet, the Drosophila Evi1 and Prdm16 proto-oncogene homolog, modifies cellular responses to these iteratively used Notch signals in a context-dependent manner, and controls odorant receptor gene choice and ORN axon targeting specificity. In nascent ORNs, Hamlet erases the Notch state inherited from the parental cell, enabling a modified response in a subsequent round of Notch signaling. Hamlet directs locus-specific modifications of histone methylation and histone density and controls accessibility of the DNA-binding protein Suppressor of Hairless at the Notch target promoter.

Prdm proto-oncogene transcription factor family expression and interaction with the Notch-Hes pathway in mouse neurogenesis.

BACKGROUND: Establishment and maintenance of a functional central nervous system (CNS) requires a highly orchestrated process of neural progenitor cell proliferation, cell cycle exit, and differentiation. An evolutionary conserved program consisting of Notch signalling mediated by basic Helix-Loop-Helix (bHLH) transcription factor activity is necessary for both the maintenance of neural progenitor cell character and the progression of neurogenesis; however, additional players in mammalian CNS neural specification remain largely unknown. In Drosophila we recently characterized Hamlet, a transcription factor that mediates Notch signalling and neural cell fate. METHODOLOGY/PRINCIPAL FINDINGS: Hamlet is a member of the Prdm (PRDI-BF1 and RIZ homology domain containing) proto-oncogene transcription factor family, and in this study we report that multiple genes in the Prdm family (Prdm6, 8, 12, 13 and 16) are expressed in the developing mouse CNS in a spatially and temporally restricted manner. In developing spinal cord Prdm8, 12 and 13 are expressed in precise neuronal progenitor zones suggesting that they may specify discrete neuronal subtypes. In developing telencephalon Prdm12 and 16 are expressed in the ventricular zone in a lateral to medial graded manner, and Prdm8 is expressed in a complementary domain in postmitotic neurons. In postnatal brain Prdm8 additionally shows restricted expression in cortical layers 2/3 and 4, the hippocampus, and the amygdala. To further elucidate roles of Prdm8 and 16 in the developing telencephalon we analyzed the relationship between these factors and the bHLH Hes (Hairy and enhancer of split homolog) effectors of Notch signalling. In Hes null telencephalon neural differentiation is enhanced, Prdm8 expression is upregulated, and Prdm16 expression is downregulated; conversely in utero electroporation of Hes1 into the developing telencephalon upregulates Prdm16 expression. CONCLUSIONS/SIGNIFICANCE: Our data demonstrate that Prdm genes are regulated by the Notch-Hes pathway and represent strong candidates to control neural class specification and the sequential progression of mammalian CNS neurogenesis.

Knot/Collier and cut control different aspects of dendrite cytoskeleton and synergize to define final arbor shape.

In a complex nervous system, neuronal functional diversity is reflected in the wide variety of dendritic arbor shapes. Different neuronal classes are defined by class-specific transcription factor combinatorial codes. We show that the combination of the transcription factors Knot and Cut is particular to Drosophila class IV dendritic arborization (da) neurons. Knot and Cut control different aspects of the dendrite cytoskeleton, promoting microtubule- and actin-based dendritic arbors, respectively. Knot delineates class IV arbor morphology by simultaneously synergizing with Cut to promote complexity and repressing Cut-mediated promotion of dendritic filopodia/spikes. Knot increases dendritic arbor outgrowth through promoting the expression of Spastin, a microtubule-severing protein disrupted in autosomal dominant hereditary spastic paraplegia (AD-HSP). Knot and Cut may modulate cellular mechanisms that are conserved between Drosophila and vertebrates. Hence, this study gives significant general insight into how multiple transcription factors combine to control class-specific dendritic arbor morphology through controlling different aspects of the cytoskeleton.