Septamer element-binding proteins in neuronal and glial differentiation

Vascular endothelial growth factor is involved in mediating increased de novo hippocampal neurogenesis in response to traumatic brain injury

Stimulating the endogenous repair process after traumatic brain injury (TBI) can be an important approach in neuroregenerative medicine. Vascular endothelial growth factor (VEGF) is one of the molecules that can increase de novo hippocampal neurogenesis. Here, we tested whether VEGF signaling through Flk1 (VEGF receptor 2) is involved in the neurogenic process after experimental TBI. We found that Flk1 is expressed both by neuroblasts in the subgranular layer (SGL) and by maturing granule neurons in the adult dentate gyrus (DG) of the hippocampus. After lateral fluid percussion TBI (LFP-TBI) in the rat, we detected elevated VEGF levels and also increased numbers of de novo neurons in the ipsilateral DG. To test the involvement of VEGF and Flk1 in the neurogenic process directly, we delivered recombinant VEGF or SU5416, an inhibitor to Flk1, into the ipsilateral cerebral ventricle of injured animals. We found that VEGF infusion significantly increased the number of BrdU+/Prox1+ new neurons, decreased the number of TUNEL+ cells, but did not change the number of BrdU+ newborn cells per se. Infusion with SU5416 caused no significant changes. Our results suggest that (a) VEGF is a part of the molecular signaling network that mediates de novo hippocampal neurogenesis after TBI; (b) VEGF predominantly mediates survival of de novo granule neurons rather than proliferation of neuroblasts in the injured brain; and (c) additional VEGF receptor(s) and/or other molecular mechanism(s) are also involved in mediating increased neurogenesis following injury.

Ikaros is expressed in developing striatal neurons and involved in enkephalinergic differentiation

The Ikaros (Ik) gene encodes alternatively spliced zinc-finger proteins originally identified in developing hematopoietic organs and acts as master regulator of lymphoid development. During our search for transcription factors that control the developmental expression of the enkephalin (ENK) gene we found that Ik-1 and Ik-2 isoforms are specifically expressed in the embryonic striatum and bind the Ik-like cis-regulatory DNA element present on the ENK gene. Ik proteins are expressed by both proliferating (BrdU+/nestin+) and by post-mitotic differentiating (MAP2+) cells in the developing striatum between embryonic day 12 and post-natal day 2 and mRNAs encoding for the Ik and ENK genes are co-expressed by a subset of differentiating striatal neurons. Blocking the DNA binding of Ik proteins in differentiating embryonic striatal neuronal cultures resulted in decreased ENK expression and mutant animals lacking the DNA-binding domain of Ik had a deficit in the number of ENK but not in dynorphin or substance P mRNA+ cells. Animals lacking the protein interaction domain of Ik showed no deficit. These results demonstrate that Ik-1 and Ik-2 proteins through their DNA binding act as positive regulators of ENK gene expression in the developing striatum and participate in regulating enkephalinergic differentiation.

AUF1 is expressed in the developing brain, binds to AT-rich double-stranded DNA, and regulates enkephalin gene expression

During our search for transcriptional regulators that control the developmentally regulated expression of the enkephalin (ENK) gene, we identified AUF1. ENK, a peptide neurotransmitter, displays precise cell-specific expression in the adult brain. AUF1 (also known as heterogeneous nuclear ribonucleoprotein D) has been known to regulate gene expression through altering the stability of AU-rich mRNAs. We show here that in the developing brain AUF1 proteins are expressed in a spatiotemporally defined manner, and p37 and p40/42 isoforms bind to an AT-rich double-stranded (ds) DNA element of the rat ENK (rENK) gene. This AT-rich dsDNA sequence acts as a cis-regulatory DNA element and is involved in regulating the cell-specific expression of the ENK gene in primary neuronal cultures. The AT-rich dsDNA elements are present at approximately 2.5 kb 5'upstream of the rat, human, and mouse ENK genes. AUF1 proteins are shown here to provide direct interaction between these upstream AT-rich DNA sequences and the TATA region of the rENK gene. Double immunohistochemistry demonstrated that in the developing brain AUF1 proteins are expressed by proliferating neural progenitors and by differentiating neurons populating brain regions, which will not express the ENK gene in the adult, suggesting a repressor role for AUF1 proteins during enkephalinergic differentiation. Their subnuclear distribution and interactions with AT-rich DNA suggest that in the developing brain they can be involved in complex nuclear regulatory mechanisms controlling the development- and cell-specific expression of the ENK gene.

Isolation and characterization of SATB2, a novel AT-rich DNA binding protein expressed in development- and cell-specific manner in the rat brain

AT-rich DNA elements play an important role in regulating cell-specific gene expression. One of the AT-rich DNA binding proteins, SATB1 is a novel type of transcription factor that regulates gene expression in the hematopoietic lineage through chromatin modification. Using DNA-affinity purification followed by mass spectrometry we identified and isolated a related protein, SATB2 from the developing rat cerebral cortex. SATB2 shows homology to SATB1 and the rat protein is practically identical to the mouse and human SATB2. Using competitive EMSA, we show that recombinant SATB2 protein binds with high affinity and specificity to AT-rich dsDNA. Using RT-PCR, Western analysis and immunohistochemistry we demonstrate that SATB2 expression is restricted to a subset of postmitotic, differentiating neurons in the rat neocortex at ages E16 and P4. We suggest that similar to its homologue SATB1, SATB2 is also involved in regulating gene expression through altering chromatin structure in differentiating cortical neurons.

Far-upstream elements are dispensable for tissue-specific proenkephalin expression using a Cre-mediated knock-in strategy

Several cis-regulatory DNA elements are present in the 5' upstream regulatory region of the enkephalin gene (ENK) promoter. To determine their role in conferring organ-specificity of ENK expression in mice and to circumvent the position effects from random gene insertion that are known to often frustrate such analysis in transgenic mice, we used a Cre-mediated gene knock-in strategy to target reporter constructs to a "safe haven" loxP-tagged locus in the hypoxanthine phosphoribosyltransferase (HPRT) gene. Here we report reliable and reproducible reporter gene expression under the control of the 5' upstream regulatory region of the mouse ENK gene in gene-modified mice using this Cre-mediated knock-in strategy. Comparison of two 5'ENK regulatory regions (one with and the other without known cis-regulatory DNA elements) in the resulting adult mice showed that conserved far-upstream cis-regulatory DNA elements are dispensable for correct organ-specific gene expression. Thus the proximal 1.4 kb of the murine ENK promoter region is sufficient for organ-specificity of ENK gene expression when targeted to a safe-haven genomic locus. These results suggest that conservation of the far-upstream DNA elements serves more subtle roles, such as the developmental or cell-specific expression of the ENK gene.

Defense and Veterans Head Injury Program: background and overview

Traumatic brain injury (TBI) is the principal cause of death and disability for young Americans, with an estimated societal cost of over $39 billion per year. The Defense and Veterans Head Injury Program (DVHIP) represents a close collaboration among the Departments of Defense (DoD) and Veterans Affairs (DVA), the Brain Injury Association (BIA), and the International Brain Injury Association (IBIA). Its principal mission is to ensure that military and veteran patients with head injury receive TBI-specific evaluation, treatment, rehabilitation, and follow-up, while at the same time addressing the readiness mission of the military and helping to define optimal care for victims of TBI nationwide. Defense and Veterans Head Injury Program activities can be grouped into three broad classes: (1) TBI education, community service, and primary prevention projects; (2) combined TBI clinical treatment, rehabilitation, and clinical research projects; and (3) clinically linked TBI laboratory research projects. It is thus based on a prudent integration of clinical care and follow-up with programmatic clinical and clinically related laboratory research, TBI prevention, and education. This previously nonexistent clinical infrastructure now offers a valuable base for ongoing TBI clinical research.