Biology subjects

Salomone, J.

Publications and source records attributed to Salomone, J..

3 recordsLinked to original sources

bioRxiv2020

Gli3 utilizes Hand2 to synergistically regulate tissue-specific transcriptional networks

Despite a common understanding that Gli TFs are utilized to reiterate a Hh morphogen gradient, genetic analyses suggest craniofacial development does not completely fit this paradigm. We demonstrated that rather than being driven by a Hh threshold, robust Gli3 transcriptional activity during skeletal and glossal development required interaction with the bHLH TF Hand2. Not only did genetic and expression data support a co-factorial relationship, but genomic analysis further revealed that Gli3 and Hand2 were enriched at regulatory elements for genes essential for mandibular patterning and development. Interestingly, motif analysis at sites co-occupied by Gli3 and Hand2 uncovered mandibular-specific, low-affinity, divergent Gli binding motifs (dGBMs). Functional validation revealed these dGBMs conveyed synergistic activation of Gli targets essential for mandibular patterning and development. In summary, this work elucidates a novel, sequence-dependent mechanism for Gli transcriptional activity within the craniofacial complex that is independent of a graded Hh signal.

developmental biology↗

bioRxiv2019

Physical interactions between Gsx2 and Ascl1 regulate the balance between progenitor expansion and neurogenesis in the mouse lateral ganglionic eminence

The Gsx2 homeodomain transcription factor is required to maintain neural progenitor identity in the lateral ganglionic eminence (LGE) within the developing ventral telencephalon, despite its role in upregulating the neurogenic factor Ascl1. How Gsx2 maintains cells as progenitors in the presence of a pro-differentiation factor is unclear. Here, we show that Gsx2 and Ascl1 are co-expressed in dividing subapical progenitors within the LGE ventricular zone (VZ). Moreover, we show that while Ascl1 misexpression promotes neurogenesis in dorsal telencephalic progenitors that do not express Gsx2, co-expression of Gsx2 with Ascl1 inhibits neurogenesis in these cells. To investigate the mechanisms underlying this inhibition, we used a cell-based luciferase assay to show that Gsx2 reduced the ability of Ascl1 to activate target gene expression in a dose-dependent and DNA binding-independent manner. Yeast 2-hybrid and co-immunoprecipitation assays revealed that Gsx2 physically interacts with the basic-Helix-Loop-Helix (bHLH) domain of Ascl1, and DNA binding assays demonstrated that this interaction interferes with the ability of Ascl1 to form homo- or heterodimers with E-proteins such as Tcf3 on DNA. To further assess for in vivo molecular interactions between these transcription factors within the telencephalon, we modified a proximity ligation assay for embryonic tissue sections and found that Ascl1:Gsx2 interactions are enriched within VZ progenitors, whereas Ascl1:Tcf3 interactions predominate in basal progenitors. Altogether, these findings suggest that physical interactions between Gsx2 and Ascl1 limit Ascl1:Ascl1 and Ascl1:Tcf3 interactions, and thereby inhibit Ascl1-dependennt neurogenesis and allow for progenitor expansion within the LGE.

neuroscience↗

bioRxiv2019

Enhancer architecture sensitizes cell specific responses to Notch gene dose via a bind and discard mechanism

Notch pathway haploinsufficiency can cause severe developmental syndromes with highly variable penetrance. Currently, we have a limited mechanistic understanding of phenotype variability due to gene dosage. Here, we show that inserting a single enhancer containing pioneer transcription factor sites coupled to Notch dimer sites can unexpectedly induce a subset of Drosophila Notch haploinsufficiency phenotypes in an animal with wild type Notch gene dose. Mechanistically, this enhancer couples Notch DNA binding to degradation in a Cdk8-dependent, transcription-independent manner. Using mathematical modeling combined with quantitative trait and expression analysis, we show that tissues requiring long duration Notch signals are more sensitive to perturbations in Notch degradation compared to tissues relying upon short duration processes. These findings support a novel \"bind and discard\" mechanism in which enhancers with specific binding sites promote rapid Notch turnover, reduce Notch-dependent transcription at other loci, and thereby sensitize tissues to gene dose based upon signal duration.

developmental biology↗