Genetic interaction between Lef1 and Alx4 is required for early embryonic development

Lymphoid Enhancer Factor-1 (Lef1) facilitates the assembly of transcriptional regulatory complexes and mediates nuclear responses to Wnt signals. We determined previously that the mesenchymally restricted, paired-like homeodomain protein Aristaless-like 4 (Alx4) interacts with Lef1 and together alters promoter activity of candidate genes. In order to define their overlapping functions, mice deficient for both Lef1 and Alx4 activity (Lef1^-/-/Alx4^lstD/lstD) were produced. Whereas embryos lacking either Lef1 or Alx4 activity remain viable up to or after birth, early embryonic lethality results when both factors were absent. No viable Lef1^-/-/Alx4^lstD/lstD embryos were recovered beyond 9.5 dpc. Between E8.5 and E10, viable Lef1^-/-/Alx4^lstD/lstD embryos were developmentally delayed 0.5 days relative to littermates of all other genotypes. Principle among the alterations seen in Lef1^-/-/Alx4^lstD/lstD animals was defective vasculature in both embryonic and extra-embryonic tissues. In the yolk sac, while the vascular network is present, it were greatly diminished and large vitelline vessels were largely absent. Platelet/endothelial cell adhesion molecule (PECAM) staining revealed that the major vessels in the head of compound mutant embryos were absent, while the other vessels were finer than those seen in normal littermates. Pools of blood and pericardial effusion were also apparent in Lef1^-/-/Alx4^lstD/lstD animals, further indicative of a defective vasculature. These data confirm genetically the interaction between Lef1 and Alx4 and further reveal unknown, overlapping roles for these transcription factors in embryonic vasculogenesis

Identification of the regions involved in DNA binding by the mouse PEBP2α protein

AbstractThe polyomavirus enhancer binding protein 2α (PEBP2α) is a DNA binding transcriptional regulatory protein that binds conserved sites in the polyomavirus enhancer, mammalian type C retroviral enhancers and T-cell receptor gene enhancers. Binding of PEBP2α and homologous proteins to the consensus DNA sequence TGPyGGTPy is mediated through a protein domain known as the runt domain. Although recent NMR studies of DNA-bound forms of the runt domain have shown an immunoglobulin-like (Ig) fold, the identification of residues of the protein that are involved in DNA binding has been obscured by the low solubility of the runt domain. Constructs of the mouse PEBP2αA1 gene were generated with N- and C-terminal extensions beyond the runt homology region. The construct containing residues Asp90 to Lys225 of the sequence (PEBP2α90–225) yielded soluble protein. The residues that participate in DNA binding were determined by comparing the NMR spectra of free and DNA-bound PEBP2α90–225. Analysis of the changes in the NMR spectra of the two forms of the protein by chemical shift deviation mapping allowed the unambiguous determination of the regions that are responsible for specific DNA recognition by PEBP2α. Five regions in PEBP2α90–225 that are localized at one end of the β-barrel were found to interact with DNA, similar to the DNA binding interactions of other Ig fold proteins

Two Regulatory Elements for Immunoglobulin kappa Light Chain Gene Expression

By using internal deletions within a rearranged immunoglobulin kappa light chain gene, the presence of an intron regulatory sequence (enhancer) has been confirmed. Its presence is required for high-level transcription from a plasmid after transfection into myeloma cells. Transfection efficiency was monitored by the activity of a deleted H4 histone gene included in the plasmid. The intron element could be moved upstream of the gene in both orientations, fulfilling the definition of an enhancer. By using 5' deletions, a second regulatory element was located upstream of the "TATA" box, between positions -69 and -104. These two elements both are required for efficient kappa chain gene expression

Satb2 Regulates Callosal Projection Neuron Identity in the Developing Cerebral Cortex

SummarySatb2 is a DNA-binding protein that regulates chromatin organization and gene expression. In the developing brain, Satb2 is expressed in cortical neurons that extend axons across the corpus callosum. To assess the role of Satb2 in neurons, we analyzed mice in which the Satb2 locus was disrupted by insertion of a LacZ gene. In mutant mice, β-galactosidase-labeled axons are absent from the corpus callosum and instead descend along the corticospinal tract. Satb2 mutant neurons acquire expression of Ctip2, a transcription factor that is necessary and sufficient for the extension of subcortical projections by cortical neurons. Conversely, ectopic expression of Satb2 in neural stem cells markedly decreases Ctip2 expression. Finally, we find that Satb2 binds directly to regulatory regions of Ctip2 and induces changes in chromatin structure. These data suggest that Satb2 functions as a repressor of Ctip2 and regulatory determinant of corticocortical connections in the developing cerebral cortex

Enhancer decommissioning by Snail1-induced competitive displacement of TCF7L2 and down-regulation of transcriptional activators results in EPHB2 silencing

Transcriptional silencing is a major cause for the inactivation of tumor suppressor genes, however, the underlying mechanisms are only poorly understood. The EPHB2 gene encodes a receptor tyrosine kinase that controls epithelial cell migration and allocation in intestinal crypts. Through its ability to restrict cell spreading, EPHB2 functions as a tumor suppressor in colorectal cancer whose expression is frequently lost as tumors progress to the carcinoma stage. Previously we reported that EPHB2 expression depends on a transcriptional enhancer whose activity is diminished in EPHB2 non-expressing cells. Here we investigated the mechanisms that lead to EPHB2 enhancer inactivation. We show that expression of EPHB2 and SNAIL1 - an inducer of epithelial-mesenchymal transition (EMT) - is anti-correlated in colorectal cancer cell lines and tumors. In a cellular model of Snail1-induced EMT, we observe that features of active chromatin at the EPHB2 enhancer are diminished upon expression of murine Snail1. We identify the transcription factors FOXA1, MYB, CDX2 and TCF7L2 as EPHB2 enhancer factors and demonstrate that Snail1 indirectly inactivates the EPHB2 enhancer by downregulation of FOXA1 and MYB. In addition, Snail1 induces the expression of Lymphoid enhancer factor 1 (LEF1) which competitively displaces TCF7L2 from the EPHB2 enhancer. In contrast to TCF7L2, however, LEF1 appears to repress the EPHB2 enhancer. Our findings underscore the importance of transcriptional enhancers for gene regulation under physiological and pathological conditions and show that SNAIL1 employs a combinatorial mechanism to inactivate the EPHB2 enhancer based on activator deprivation and competitive displacement of transcription factors

A functional component of the sea urchin H2A gene modulator contains an extended sequence homology to a viral enhancer

The DNA sequences imparting a maximal rate of sea urchin H2A gene transcription in the frog oocyte nucleus were narrowed down by deletion mapping to a DNA segment -165 to -111, far-upstream of the H2A mRNA cap site. C to T base changes in this area create strong down mutations, hence the primary structure of this DNA sequence is of paramount importance to the H2A gene expression. Sequence comparisons suggest that the -165 to -111 region may contain two essential sequence blocks. Most strikingly, the -135 area contains a 14 out of 17 basepair homology to the Moloney murine sarcoma virus enhancer and to topologically related 5' LTR-sequences of the simian sarcoma virus and the murine Friend spleen focus forming virus

Memories of lost enhancers

Transcriptional enhancers are key determinants of developmentally regulated gene expression. Models of enhancer function must distinguish between analog or digital control of transcription, as well as their requirement to initiate or maintain transcriptional activity of a gene. In light of a recent study by Chong and colleagues (pp. 659–669) providing evidence of a transient requirement of an enhancer associated with the CD4 gene, we discuss possible mechanisms by which transcriptional memory can be propagated in the absence of enhancers