Forward to the special issue on Hox/Tale transcription factors in development and disease

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/102217/1/dvdy24098.pd

MEKK2 mediates aberrant ERK activation in neurofibromatosis type I

Neurofibromatosis type I (NF1) is characterized by prominent skeletal manifestations caused by NF1 loss. While inhibitors of the ERK activating kinases MEK1/2 are promising as a means to treat NF1, the broad blockade of the ERK pathway produced by this strategy is potentially associated with therapy limiting toxicities. Here, we have sought targets offering a more narrow inhibition of ERK activation downstream of NF1 loss in the skeleton, finding that MEKK2 is a novel component of a noncanonical ERK pathway in osteoblasts that mediates aberrant ERK activation after NF1 loss. Accordingly, despite mice with conditional deletion of Nf1 in mature osteoblasts (Nf1(fl/fl);Dmp1-Cre) and Mekk2(-/-) each displaying skeletal defects, Nf1(fl/fl);Mekk2(-/-);Dmp1-Cre mice show an amelioration of NF1-associated phenotypes. We also provide proof-of-principle that FDA-approved inhibitors with activity against MEKK2 can ameliorate NF1 skeletal pathology. Thus, MEKK2 functions as a MAP3K in the ERK pathway in osteoblasts, offering a potential new therapeutic strategy for the treatment of NF1

Ablation of the renal stroma defines its critical role in nephron progenitor and vasculature patterning

The renal stroma is an embryonic cell population located in the cortex that provides a structural framework as well as a source of endothelial progenitors for the developing kidney. The exact role of the renal stroma in normal kidney development hasn't been clearly defined. However, previous studies have shown that the genetic deletion of Foxd1, a renal stroma specific gene, leads to severe kidney malformations confirming the importance of stroma in normal kidney development. This study further investigates the role of renal stroma by ablating Foxd1-derived stroma cells themselves and observing the response of the remaining cell populations. A Foxd1cre (renal stroma specific) mouse was crossed with a diphtheria toxin mouse (DTA) to specifically induce apoptosis in stromal cells. Histological examination of kidneys at embryonic day 13.5-18.5 showed a lack of stromal tissue, mispatterning of renal structures, and dysplastic and/or fused horseshoe kidneys. Immunofluorescence staining of nephron progenitors, vasculature, ureteric epithelium, differentiated nephron progenitors, and vascular supportive cells revealed that mutants had thickened nephron progenitor caps, cortical regions devoid of nephron progenitors, aberrant vessel patterning and thickening, ureteric branching defects and migration of differentiated nephron structures into the medulla. The similarities between the renal deformities caused by Foxd1 genetic knockout and Foxd1DTA mouse models reveal the importance of Foxd1 in mediating and maintaining the functional integrity of the renal stroma. © 2014 Hum et al

Hox10 Genes Function in Kidney Development in the Differentiation and Integration of the Cortical Stroma

Organogenesis requires the differentiation and integration of distinct populations of cells to form a functional organ. In the kidney, reciprocal interactions between the ureter and the nephrogenic mesenchyme are required for organ formation. Additionally, the differentiation and integration of stromal cells are also necessary for the proper development of this organ. Much remains to be understood regarding the origin of cortical stromal cells and the pathways involved in their formation and function. By generating triple mutants in the Hox10 paralogous group genes, we demonstrate that Hox10 genes play a critical role in the developing kidney. Careful examination of control kidneys show that Foxd1-expressing stromal precursor cells are first observed in a cap-like pattern anterior to the metanephric mesenchyme and these cells subsequently integrate posteriorly into the kidney periphery as development proceeds. While the initial cap-like pattern of Foxd1-expressing cortical stromal cells is unaffected in Hox10 mutants, these cells fail to become properly integrated into the kidney, and do not differentiate to form the kidney capsule. Consistent with loss of cortical stromal cell function, Hox10 mutant kidneys display reduced and aberrant ureter branching, decreased nephrogenesis. These data therefore provide critical novel insights into the cellular and genetic mechanisms governing cortical cell development during kidney organogenesis. These results, combined with previous evidence demonstrating that Hox11 genes are necessary for patterning the metanephric mesenchyme, support a model whereby distinct populations in the nephrogenic cord are regulated by unique Hox codes, and that differential Hox function along the AP axis of the nephrogenic cord is critical for the differentiation and integration of these cell types during kidney organogenesis

Hox genes in the adult skeleton: Novel functions beyond embryonic development

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/136346/1/dvdy24482.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136346/2/dvdy24482_am.pd

Hox Function in Mammalian Kidney Development.

The Hox gene complexes encode an evolutionarily conserved set of transcription factors important for the anteroposterior (AP) patterning of the body plan, and are essential for the proper development of many organ systems, including the kidney. The purpose of my work was to delineate the mechanisms involved in Hox patterning of the kidney. The Hox11 genes are necessary for the initial stage of metanephric kidney development. Six2 and Gdnf, factors required for ureteric bud outgrowth into the kidney mesenchyme, are absent in the metanephric mesenchyme of Hox11 mutant animals. Using genetic, molecular, and biochemical assays, we showed that Hox11 proteins interact with Pax2 and Eya1, which are novel Hox cofactors, to directly regulate the expression of Six2 and Gdnf. We also identified a single enhancer site, a Hox response element (HRE), in the Six2 promoter that is necessary for Hox11-Pax2-Eya1 mediated activation of Six2 in vitro and in vivo. Transgenic mutation of the Six2 enhancer additionally demonstrated that the HRE required for activation of Six2 in the kidney is also necessary for repression of Six2 in the head mesenchyme, a phenotype previously reported in Hoxa2 loss-of-function mutants. Thus, Hoxa11 activation and Hoxa2 repression use the same HRE to regulate Six2 expression. To investigate how Hox proteins confer differential activation and repression of Six2 we used a combination of protein domain swaps and cell culture reporter analyses. We demonstrated that DNA binding is required for Hox protein function, but the regions N- and C-terminal to the homeodomain confer the differential activities of Hoxa2 and Hoxa11. Concurrent with these molecular analyses of the function of Hox11 in kidney organogenesis, I have also demonstrated that the Hox10 paralogous genes are necessary for proper kidney development. Morphological analyses and gene expression studies showed that the Hox10 genes are necessary for patterning the cortical stromal cell compartment in the developing kidney and regulate the formation of the renal capsule.Ph.D.Cell and Developmental BiologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/63845/1/alishay_1.pd