Biology subjects

Bengani, H.

Publications and source records attributed to Bengani, H..

4 recordsLinked to original sources

bioRxiv2024

Neanderthal-derived variants shape craniofacial enhancer activity at a human disease locus

Facial appearance is one of the most variable morphological traits in humans, influenced by both rare and common genetic variants that can impact facial form between individuals and in disease. Deletion of an enhancer cluster 1.45 megabases upstream of the SOX9 gene (EC1.45) results in Pierre Robin sequence, a human craniofacial disorder characterised by underdevelopment of the lower jaw and frequently associated with cleft palate. We reasoned that single nucleotide variants in EC1.45 may cause more subtle alterations to facial morphology. Here, we took advantage of recent human evolution, and the distinct morphology of the Neanderthal lower jaw, to investigate the impact of three Neanderthal-derived single nucleotide variants on EC1.45 function and jaw development. Utilising a dual enhancer-reporter system in zebrafish, we observed enhanced Neanderthal regulatory activity relative to the human orthologue during a specific developmental window. At this same stage, we show that EC1.45 appears to be selectively active in neural crest- derived progenitor cells which lie in close apposition with and are transcriptionally related to precartilaginous condensations that contribute to craniofacial skeletal development. To examine the potential consequences of increased SOX9 expression in this specific cellular population during jaw development, we overexpressed human SOX9 specifically in EC1.45-active cells and observed an increase in the volume of developing cartilaginous precursors. Taken together, our work implicates Neanderthal-derived variants in increased regulatory activity for a disease- associated enhancer with the potential to impact craniofacial skeletal development and jaw morphology across recent hominin evolution.

genetics↗

bioRxiv2022

Characterization of an Eye Field-like State during Optic Vesicle Organoid Development

Specification of the eye field (EF) within the neural plate marks the earliest detectable stage of eye development. Experimental evidence, primarily from non-mammalian model systems, indicates that the stable formation of this group of cells requires the activation of a set of key transcription factors (TFs). This critical event is challenging to probe in mammals and, quantitatively, little is known regarding the regulation of the transition of cells to this ocular fate. Using optic vesicle organoids to model the onset of the EF, we generate timecourse transcriptomic data allowing us to identify dynamic gene-expression programs that characterise this cellular-state transition. Integrating this with chromatin accessibility data suggests a direct role of canonical EFTFs in regulating these gene-expression changes, and high-lights candidate cis-regulatory elements through which these TFs act. Finally, we begin to test a subset of these candidate enhancer elements, within the organoid system, by perturbing the underlying DNA sequence and measuring transcriptomic changes during EF activation.

developmental biology↗

bioRxiv2022

Robust genetic analysis of the X-linked anophthalmic (Ie) mouse

Anophthalmia (missing eye) describes a failure of early embryonic ocular development. Mutations in a relatively small set of genes account for 75% of bilateral anophthalmia cases, yet 25% of families currently are left without a molecular diagnosis. Here we report our experimental work that aimed to uncover the developmental and genetic basis of the anophthalmia characterising the X-linked Ie (eye-ear reduction) X-ray induced allele in mouse that was first identified in 1947. Histological analysis of the embryonic phenotype showed failure of normal eye development after the optic vesicle stage with particularly severe malformation of the ventral retina. Linkage analysis mapped this mutation to a [~] 6Mb region on the X chromosome. Short and long read whole-genome sequencing (WGS) of affected and unaffected male littermates confirmed the Ie linkage but identified no plausible causative variants or structural rearrangements. These analyses did reduce the critical candidate interval and revealed evidence of multiple variants within the ancestral DNA, although none were found that altered coding sequences or that were unique to Ie. To investigate early embryonic events at a genetic level, we then generated mouse ES cells derived from male Ie embryos and wild type littermates. RNA-seq and accessible chromatin sequencing (ATAC-seq) data generated from cultured optic vesicle organoids did not reveal any large differences in gene expression or accessibility of putative cis-regulatory elements between Ie and wild type. However, an unbiased TF-footprinting analysis of accessible chromatin regions did provide evidence of a genome-wide reduction in binding of transcription factors associated with ventral eye development in Ie, and evidence of an increase in binding of the Zic-family of transcription factors, including Zic3, which is located within the Ie-refined critical interval. We conclude that the refined Ie critical region at chrX: 56,145,000-58,385,000 contains multiple genetic variants that may be linked to altered cis regulation but does not contain a convincing causative mutation. Changes in the binding of key transcription factors to chromatin causing altered gene expression during development, possibly through a subtle mis-regulation of Zic3, presents a plausible cause for the anophthalmia phenotype observed in Ie, but further work is required to determine the precise causative allele and its genetic mechanism.

genetics↗

bioRxiv2020

Functional Predictors of Causative Cis-Regulatory Mutations in Mendelian Disease

Undiagnosed neurodevelopmental disease is significantly associated with rare variants in cis-regulatory elements (CRE) but demonstrating causality is challenging as target gene consequences may differ from a causative variant affecting the coding region. Here, we address this challenge by applying a procedure to discriminate likely diagnostic regulatory variants from those of neutral/low-penetrant effect. We identified six rare CRE variants using targeted and whole genome sequencing in 48 unrelated males with apparent X-linked intellectual disability (XLID) but without detectable coding region variants. These variants segregated appropriately in families and altered conserved bases in predicted CRE targeting known XLID genes. Three were unique and three were rare but too common to be plausibly causative for XLID. We compared the cis-regulatory activity of wild-type and mutant alleles in zebrafish embryos using dual-color fluorescent reporters. Two variants showed striking changes: one plausibly causative (FMR1CRE) and the other likely neutral/low-penetrant (TENM1CRE). These variants were "knocked-in" to mice and both altered embryonic neural expression of their target gene. Only Fmr1CRE mice showed disease-relevant behavioral defects. FMR1CRE is plausibly disease-associated resulting in complex misregulation of Fmr1/FMRP rather than loss-of-function. This is consistent both with absence of Fragile X syndrome in the probands and the observed electrophysiological anomalies in the FMR1CRE mouse brain. Although disruption of in vivo patterns of endogenous gene expression in disease-relevant tissues by CRE variants cannot be used as strong evidence for Mendelian disease association, in conjunction with extreme rarity in human populations and with relevant knock-in mouse phenotypes, such variants can become likely pathogenic.

genetics↗