Browsing by Author "Tandon, Bhavna"

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    Role ofﾠWNT10Aﾠin failure of tooth development in humans and zebrafish
    (Wiley, 2017) Yuan, Qiuping; Zhao, Min; Tandon, Bhavna; Maili, Lorena; Liu, Xiaoming; Zhang, Anqi; Baugh, Evan H.; Tran, Tam; Silva, Renato M.; Hecht, Jacqueline T.; Swindell, Eric C.; Wagner, Daniel S.; Letra, Ariadne
    Background: Oligodontia is a severe form of tooth agenesis characterized by the absence of six or more permanent teeth. Oligodontia has complex etiology and variations in numerous genes have been suggested as causal for the condition. Methods: We applied whole‐exome sequencing (WES) to identify the cause of oligodontia in a 9‐year‐old girl missing 11 permanent teeth. Protein modeling and functional analysis in zebrafish were also performed to understand the impact of identified variants on the phenotype. Results: We identified a novel compound heterozygous missense mutation in WNT10A (c.637G>A:p.Gly213Ser and c.1070C>T:p.Thr357Ile) as the likely cause of autosomal recessive oligodontia in the child. Affected residues are located in conserved regions and variants are predicted to be highly deleterious for potentially destabilizing the protein fold and inhibiting normal protein function. Functional studies in zebrafish embryos showed that wnt10a is expressed in the craniofacies at critical time points for tooth development, and that perturbations of wnt10a expression impaired normal tooth development and arrested tooth development at 5 days postfertilization (dpf). Furthermore, mRNA expression levels of additional tooth development genes were directly correlated with wnt10a expression; expression of msx1, dlx2b, eda, and axin2 was decreased upon wnt10a knockdown, and increased upon wnt10a overexpression. Conclusions: Our results reveal a novel compound heterozygous variant in WNT10A as pathogenic for oligodontia, and demonstrate that perturbations of wnt10a expression in zebrafish may directly and/or indirectly affect tooth development recapitulating the agenesis phenotype observed in humans.
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    The role of MK2/TTP pathway in regulating early development and innate immunity in zebrafish
    (2018-11-30) Tandon, Bhavna; Silberg, Jonathan; Wagner, Daniel
    The origin of novel structures and the genes that regulate their formation is a challenging question that has been difficult to address. One such novel structure is the yolk syncytial layer (YSL) in teleost fishes like zebrafish. I studied the genetic pathways operating in the YSL using the betty boop (bbp) mutant. betty boop encodes mitogen activated protein kinase activated protein kinase 2a (mapkapk2a), also known as mk2a. One of the downstream targets of MK2a is an RNA binding protein Tristetraprolin (TTP). bbp mutants lose the expression of YSL specific genes mxtx1 and mxtx2. Here, we show that these genes are regulated through their 3’untranslated region (UTR) by MK2a/TTP pathway required in the YSL during early zebrafish development to limit their expression to the YSL. I developed an in vivo reporter assay to detect spatial regulation of mRNA stability by the MK2/TTP pathway in early zebrafish embryos which can also be used to test other potential TTP targets. MK2a is the zebrafish homolog of mammalian MK2. In mammals, MK2 is not active during early development but rather is required to regulate genes that are responsible for inflammatory response. I show that MK2/TTP reporters are not regulated in early Xenopus embryo either, implying that the early requirement for MK2 arose after the division of tetrapod and teleost lineages. The role of mk2a and its gene duplicate mk2b in regulating immune response has not been previously studied in zebrafish. I developed zebrafish as a model infection system for infection by multiple species of Candida, an opportunistic pathogen and cause of an increasing number of hospital acquired infections. I developed novel transgenic zebrafish lines that allow inducible ablation of different phagocyte classes and identified different inflammatory responses to different Candida species. Preliminary results using these tools show that mk2b-/- mutants show a higher susceptibility to Candida hyphal infection, demonstrating that mk2b plays a role in innate immunity. Whether that role is the same that MK2 plays in mammals in regulating inflammatory cytokines still need to be determined. Taken together, all these findings suggest a model in which the ancestral MK2/TTP pathway was co-opted in teleosts to restrict expression of the mxtx genes to the yolk cell, but also retains its function in innate immune response.