Biology subjects

Singh, M. D.

Publications and source records attributed to Singh, M. D..

4 recordsLinked to original sources

bioRxiv2024

Protective role of Pten downregulation in Huntington's Disease models

Huntingtons disease (HD) is a dominantly inherited neurodegenerative disorder that stems from the expansion of CAG repeats within the coding region of the Huntingtin gene. Currently, there exists no effective therapeutic intervention that can prevent the progression of the disease. Our investigation aims to identify a novel genetic modifier with therapeutic potential. We employ transgenic flies containing Htt93Q and Htt138Q.mRFP constructs, which encode mutant pathogenic Huntingtin proteins featuring 93 and 138 polyglutamine (Q) repeats, respectively. The resultant mutant protein causes the loss of photoreceptor neurons in the eye and a progressive loss of neuronal tissues in the brain and motor neurons in Drosophila. Several findings have demonstrated the association of HD with growth factor signaling defects. Phosphatase and tensin homolog (Pten) have been implicated in the negative regulation of insulin signaling/receptor tyrosine signaling pathway which regulates the growth and survival of cells. In the present study, we downregulated Pten and found a significant improvement in morphological phenotypes in the eye, brain, and motor neurons. These findings were further correlated with the enhancement of the functional vision and climbing ability of the flies. We also noted the reduction in both poly(Q) aggregate levels and caspase activity which are involved in the apoptotic pathway. Moreover, we elucidated the protective role of Pten inhibition through the utilization of VO-OHpic (referred to as PTENi). In alignment with the genetic modulation of Pten, pharmaceutical inhibition of Pten improved the climbing ability of flies and reduced the poly(Q) aggregates and apoptosis levels. A similar reduction in poly(Q) aggregates was observed in the mouse neuronal inducible HD cell line model. Our study illustrates that Pten inhibition is a potential therapeutic approach for HD.

neuroscience↗

bioRxiv2020

Functional assessment of the "two-hit" model for neurodevelopmental defects in Drosophila and X. laevis

We previously identified a deletion on chromosome 16p12.1 that is mostly inherited and associated with multiple neurodevelopmental outcomes, where severely affected probands carried an excess of rare pathogenic variants compared to mildly affected carrier parents. We hypothesized that the 16p12.1 deletion sensitizes the genome for disease, while "second-hits" in the genetic background modulate the phenotypic trajectory. To test this model, we examined how neurodevelopmental defects conferred by knockdown of individual 16p12.1 homologs are modulated by simultaneous knockdown of homologs of "second-hit" genes in Drosophila melanogaster and Xenopus laevis. We observed that knockdown of 16p12.1 homologs affect multiple phenotypic domains, leading to delayed developmental timing, seizure susceptibility, brain alterations, abnormal dendrite and axonal morphology, and cellular proliferation defects. Compared to genes within the 16p11.2 deletion, which has higher de novo occurrence, 16p12.1 homologs were less likely to interact with each other in Drosophila models or a human brain-specific interaction network, suggesting that interactions with "second-hit" genes may confer higher impact towards neurodevelopmental phenotypes. Assessment of 212 pairwise interactions in Drosophila between 16p12.1 homologs and 76 homologs of patient-specific "second-hit" genes (such as ARID1B and CACNA1A), genes within neurodevelopmental pathways (such as PTEN and UBE3A), and transcriptomic targets (such as DSCAM and TRRAP) identified genetic interactions in 63% of the tested pairs. In 11 out of 15 families, homologs of patient-specific "second-hits" enhanced or suppressed the phenotypic effects of one or many 16p12.1 homologs. In fact, homologs of SETD5 synergistically interacted with homologs of MOSMO in both Drosophila and X. laevis, leading to modified cellular and brain phenotypes, as well as axon outgrowth defects that were not observed with knockdown of either individual homolog. Our results suggest that several 16p12.1 genes sensitize the genome towards neurodevelopmental defects, and complex interactions with "second-hit" genes determine the ultimate phenotypic manifestation. Author SummaryCopy-number variants, or deletions and duplications in the genome, are associated with multiple neurodevelopmental disorders. The developmental delay-associated 16p12.1 deletion is mostly inherited, and severely affected children carry an excess of "second-hits" variants compared to mildly affected carrier parents, suggesting that additional variants modulate the clinical manifestation. We studied this "two-hit" model using Drosophila and Xenopus laevis, and systematically tested how homologs of "second-hit" genes modulate neurodevelopmental defects observed for 16p12.1 homologs. We observed that 16p12.1 homologs independently led to multiple neurodevelopmental features and weakly interacted with each other, suggesting that interactions with "second-hit" homologs potentially have a higher impact towards neurodevelopmental defects than interactions between 16p12.1 homologs. We tested 212 pairwise interactions of 16p12.1 homologs with "second-hit" homologs and genes within conserved neurodevelopmental pathways, and observed modulation of neurodevelopmental defects caused by 16p12.1 homologs in 11 out of 15 families, and 16/32 of these changes could be attributed to genetic interactions. Interestingly, we observed that SETD5 homologs interacted with homologs of MOSMO, which conferred additional neuronal phenotypes not observed with knockdown of individual homologs. We propose that the 16p12.1 deletion sensitizes the genome to multiple neurodevelopmental defects, and complex interactions with "second-hit" genes determine the clinical trajectory of the disorder.

genomics↗

bioRxiv2019

NCBP2-mediated apoptosis contributes to developmental defects of the schizophrenia-associated 3q29 deletion

The 1.6 Mbp deletion on chromosome 3q29 is associated with a range of neurodevelopmental disorders, including schizophrenia, autism, microcephaly, and intellectual disability. Despite its importance towards neurodevelopment, the role of individual genes, genetic interactions, and disrupted biological mechanisms underlying the deletion have not been thoroughly characterized. Here, we used quantitative methods to assay Drosophila melanogaster and Xenopus laevis models with tissue-specific individual and pairwise knockdown of 14 homologs of genes within the 3q29 region. We identified developmental, cellular, and neuronal phenotypes for multiple homologs of 3q29 genes, potentially due to altered apoptosis and cell cycle mechanisms during development. Using the fly eye, we screened for 314 pairwise knockdowns of homologs of 3q29 genes and identified 44 interactions between pairs of homologs and 34 interactions with other neurodevelopmental genes. Interestingly, NCBP2 homologs in Drosophila (Cbp20) and X. laevis (ncbp2) enhanced the phenotypes of homologs of the other 3q29 genes, leading to significant increases in apoptosis that disrupted cellular organization and brain morphology. These cellular and neuronal defects were rescued with overexpression of the apoptosis inhibitors Diap1 and xiap in both models, suggesting that apoptosis is one of several potential biological mechanisms disrupted by the deletion. NCBP2 was also highly connected to other 3q29 genes in a human brain-specific interaction network, providing support for the relevance of our results towards the human deletion. Overall, our study suggests that NCBP2-mediated genetic interactions within the 3q29 region disrupt apoptosis and cell cycle mechanisms during development. AUTHOR SUMMARYRare copy-number variants, or large deletions and duplications in the genome, are associated with a wide range of neurodevelopmental disorders. The 3q29 deletion confers an increased risk for schizophrenia, autism, and microcephaly. To understand the conserved biological mechanisms that are disrupted by this deletion, we systematically tested 14 individual homologs and 314 pairwise interactions of 3q29 genes for neuronal, cellular, and developmental phenotypes in Drosophila melanogaster and Xenopus laevis models. We found that multiple homologs of genes within the deletion region contribute towards developmental defects, such as larval lethality and disrupted cellular organization. Interestingly, we found that NCBP2 acts as a key modifier gene within the region, enhancing the developmental phenotypes of each of the homologs for other 3q29 genes and leading to disruptions in apoptosis and cell cycle pathways. Our results suggest that multiple genes within the 3q29 region interact with each other through shared mechanisms and jointly contribute to neurodevelopmental defects.

genomics↗

bioRxiv2017

Pervasive epistasis in cell proliferation pathways modulates neurodevelopmental defects of autism-associated 16p11.2 deletion

As opposed to syndromic CNVs caused by single genes, extensive phenotypic heterogeneity in variably-expressive CNVs complicates disease gene discovery and functional evaluation. Here, we propose a complex interaction model for pathogenicity of the autism-associated 16p11.2 deletion, where CNV genes interact with each other in conserved pathways to modulate expression of the phenotype. Using multiple quantitative methods in Drosophila RNAi lines, we identified a range of neurodevelopmental phenotypes for knockdown of individual 16p11.2 homologs in different tissues. We tested 565 pairwise knockdowns in the developing eye, and identified 24 interactions between pairs of 16p11.2 homologs and 46 interactions between 16p11.2 homologs and neurodevelopmental genes that suppressed or enhanced cell proliferation phenotypes compared to one-hit knockdowns. These interactions within cell proliferation pathways were also enriched in a human brain-specific network, providing translational relevance in humans. Our study indicates a role for genetic interactions within CNVs and identifies potential therapeutic targets for neurodevelopmental disorders.

genomics↗