Biology subjects

Kale, G.

Publications and source records attributed to Kale, G..

4 recordsLinked to original sources

bioRxiv2023

Divergent evolutionary strategies preempt tissue collision in fly gastrulation

Metazoan development proceeds through a series of morphogenetic events that sculpt body plans and organ structures. In the early embryonic stages, morphogenetic processes involving growth and deformation occur concurrently. Forces generated in one tissue can thus increase mechanical stress in the neighboring tissue, potentially disrupting spatial patterning, morphological robustness, and consequently decreasing organismal fitness. How organisms evolved mechanisms to reduce or release inter-tissue stresses remains poorly understood. Here we combined phylogenetic survey across a whole insect order (Diptera), quantitative live imaging, and functional mechanical perturbation to investigate the evolution of mechanical stress management during epithelial expansions in the gastrulating fly embryos. We find that two distinct cellular mechanisms exist in Diptera to prevent the accumulation of compressive stress that can arise when the expanding head and trunk tissues collide. In Cyclorrhapha, a monophyletic dipteran subgroup including the fruit fly Drosophila melanogaster, the head-trunk boundary undergoes active out-of-plane deformation to form a transient epithelial fold, called the cephalic furrow (CF), which acts as a mechanical sink to preempt head-trunk collision. Genetic or optogenetic elimination of the CF leads to tissue buckling, yielding deleterious effects of axial distortion that likely results from unmitigated release of compressive stress. Non-cyclorrhaphan flies, by contrast, lack CF formation and instead display widespread out-of-plane division in the head, which shortens the duration of its expansion and reduces surface area increase. Reorienting head mitosis in Drosophila from in-plane to out-of-plane partially suppresses the need for epithelial out-of-plane deformation, suggesting that out-of-plane division can act as an alternative mechanical sink to prevent tissue collision. Our data suggest that programs of mechanical stress management can emerge abruptly under selective pressure of inter-tissue mechanical conflict in early embryonic development.

developmental biology↗

bioRxiv2023

Elevated temperature fatally disrupts nuclear divisions in the early Drosophila embryo.

Temperature variations can challenge animal survival, with elevated temperatures presenting distinct vulnerabilities at different stages of the animal life cycle. Embryonic development is known to be especially vulnerable, though the molecular mechanisms that underlie this vulnerability remain unclear. Here we investigate how elevated temperature affects embryogenesis in Drosophila melanogaster, an insect model known for extensively characterized genetic makeup and developmental processes. We identify the first three hours as a critical window in which Drosophila embryos are particularly vulnerable to elevated temperature. This period includes the formation of a syncytial blastoderm, which involves 4 rounds of meta-synchronous nuclear divisions at the embryonic cortex, and cellularization that leads to the formation of the cellular blastoderm. Embryos exposed to elevated temperature during this period subsequently exhibited developmental defects at the gastrulation stage, leading to increased lethality. At elevated temperature, we observed an increase in mitotic failures causing a loss of cortical nuclei during cellularization. There is also a local crowding of nuclei and an increase in asynchrony between the nuclear cycles in the center vs. the poles. Interestingly, these features cooperatively amplify the frequency of mitotic failures, leading to holes in the blastoderm epithelium. Further mechanistic analysis of mitotic failures revealed that they trigger DNA damage response. Focusing on cell biological causes of mitotic failures, we found that the interaction between F-actin and microtubules is weakened at elevated temperature. We performed functional tests to determine whether known regulators of mitosis could rescue mitotic failures, blastoderm hole formation, and improve embryo survival. We further analyzed genomic datasets from wild populations to determine whether these regulators also carry signatures of adaptation in wild populations. Our genetic rescue experiments show that in Drosophila embryos, the interaction between cortical F-actin and astral microtubules of mitotic spindle is vulnerable to disruption at elevated temperatures, leading to mitotic failures that can be potentially rescued by modulating the expression of just a few factors. We propose that levels of expression of corresponding genes could be used as indicators to predict the effects of increasing temperature variations on insect populations.

developmental biology↗

bioRxiv2020

Broad transcriptomic dysregulation across the cerebral cortex in ASD

Classically, psychiatric disorders have been considered to lack defining pathology, but recent work has demonstrated consistent disruption at the molecular level, characterized by transcriptomic and epigenetic alterations.1-3 In ASD, upregulation of microglial, astrocyte, and immune signaling genes, downregulation of specific synaptic genes, and attenuation of regional gene expression differences are observed.1,2,4-6 However, whether these changes are limited to the cortical association areas profiled is unknown. Here, we perform RNA-sequencing (RNA-seq) on 725 brain samples spanning 11 distinct cortical areas in 112 ASD cases and neurotypical controls. We identify substantially more genes and isoforms that differentiate ASD from controls than previously observed. These alterations are pervasive and cortex-wide, but vary in magnitude across regions, roughly showing an anterior to posterior gradient, with the strongest signal in visual cortex, followed by parietal cortex and the temporal lobe. We find a notable enrichment of ASD genetic risk variants among cortex-wide downregulated synaptic plasticity genes and upregulated protein folding gene isoforms. Finally, using snRNA-seq, we determine that regional variation in the magnitude of transcriptomic dysregulation reflects changes in cellular proportion and cell-type-specific gene expression, particularly impacting L3/4 excitatory neurons. These results highlight widespread, genetically-driven neuronal dysfunction as a major component of ASD pathology in the cerebral cortex, extending beyond association cortices to involve primary sensory regions.

neuroscience↗

bioRxiv2019

DISTINCT ACTIN-DEPENDENT NANOSCALE ASSEMBLIES UNDERLIE THE DYNAMIC AND HIERARCHICAL ORGANIZATION OF E-CADHERIN.

Intercellular adhesion mediated by E-cadherin is pivotal in maintaining epithelial tissue integrity and for tissue morphogenesis. Adhesion requires homophilic interactions between extracellular domains of E-cadherin molecules from neighboring cells. The interaction of its cytoplasmic domains with the cortical acto-myosin network, appears to strengthen adhesion, although, it is unclear how cortical actin affects the organization and function of E-cadherin dynamically. Here we use the ectopic expression of Drosophila E-cadherin (E-cad) in larval hemocytes, which lack endogenous E-cad, to recapitulate functional cell-cell junctions in a convenient model system. We used fluorescence emission anisotropy-based microscopy and Fluorescence Correlation Spectroscopy (FCS) to probe the nanoscale organization of E-cad. We find that E-cad at cell-cell junctions in hemocytes exhibits a clustered trans-paired organization, similar to that reported for the adherens junction in the developing embryonic epithelial tissue. Further, we find that extra-junctional E-cad is also organized as relatively immobile nanoclusters as well as diffusive and more loosely packed oligomers and monomers. These oligomers are promoted by cis-interactions of the ectodomain and, strikingly, their growth is constantly counteracted by cortical actomyosin. Oligomers in turn assist in generating nanoclusters that are stabilized by cortical acto-myosin. Thus, actin remodels oligomers and stabilizes nanoclusters, revealing a requirement for actin in the dynamic organization of E-cad at the nanoscale. This dynamic organization is also present at cell-cell contacts (junction), and its disruption affects junctional integrity in the hemocyte system, as well as in the embryo. Our observations uncover a hierarchical mechanism for the nanoscale organization of E-cad, which is necessary for dynamic adhesion and maintaining junctional integrity in the face of extensive remodeling.

cell biology↗