Llgl1 regulates zebrafish cardiac development by mediating Yap stability in cardiomyocytes

Abstract

The Hippo-Yap pathway regulates multiple cellular processes in response to mechanical and other stimuli. In Drosophila, the polarity protein Lethal (2) giant larvae [L(2)gl], negatively regulates Hippo-mediated transcriptional output. However, in vertebrates, little is known about its homolog Llgl1. Here, we define a novel role for vertebrate Llgl1 in regulating Yap stability in cardiomyocytes, which impacts heart development. In contrast to the role of Drosophila L(2)gl, Llgl1 depletion in cultured rat cardiomyocytes decreased Yap protein levels and blunted target gene transcription without affecting Yap transcript abundance. Llgl1 depletion in zebrafish resulted in larger and dysmorphic cardiomyocytes, pericardial effusion, impaired blood flow and aberrant valvulogenesis. Cardiomyocyte Yap protein levels were decreased in llgl1 morphants, whereas Notch, which is regulated by hemodynamic forces and participates in valvulogenesis, was more broadly activated. Consistent with the role of Llgl1 in regulating Yap stability, cardiomyocyte-specific overexpression of Yap in Llgl1-depleted embryos ameliorated pericardial effusion and restored blood flow velocity. Altogether, our data reveal that vertebrate Llgl1 is crucial for Yap stability in cardiomyocytes and its absence impairs cardiac development.

DNA-damage induced cell death in yap1;wwtr1 mutant epidermal basal cells

“…Using previously characterized antibodies against Yap1 and Wwtr1 ( Flinn et al, 2020 ; Kimelman et al, 2017 ; Lai et al, 2018 ; Miesfeld et al, 2015 ), we investigated their cellular localization in the epidermis. Both Yap1 and Wwtr1 are localized in the nuclei of the peridermis and basal epidermis at the tailbud stage and at the 16–20 ss ( Figure 2A ).…”

“…Both Yap1 and Wwtr1 are localized in the nuclei of the peridermis and basal epidermis at the tailbud stage and at the 16–20 ss ( Figure 2A ). Yap1 is also localized to the junctions of peridermal cells ( Figure 2A ; Flinn et al, 2020 ). At these developmental stages, some EBCs in the basal epidermis lose P63 expression and differentiate into ionocytes ( Jänicke et al, 2007 ).…”

Strong as a Hippo’s Heart: Biomechanical Hippo Signaling During Zebrafish Cardiac Development

“…The depletion of the polarity protein Lethal (2) giant larvae affected Yap1 activity in cardiomyocytes and reduced their cell numbers. This caused an enlargement of cardiomyocytes and severe cardiac deficits including atrioventricular valvulogenesis defects (Flinn et al, 2020). However, these valvular deficits may be an indirect consequence caused by altered blood flow patterns in these mutants.…”

DNA-damage induced cell death in yap1;wwtr1 mutant epidermal basal cells

“…Both Yap1 and Wwtr1 are localised in the nuclei of the peridermis and basal epidermis at the tailbud stage and at the 16-20 ss (Figure 2). Yap1 is also localised to the junctions of peridermal cells (Figure 2; Flinn et al, 2020). At these developmental stages, some EBCs in the basal epidermis lose P63 expression and differentiate into ionocytes (Jänicke et al, 2007).…”

“…Using previously characterised antibodies against Yap1 and Wwtr1 (Flinn et al, 2020;Kimelman et al, 2017;Lai et al, 2018;Miesfeld et al, 2015), we investigated their cellular localisation in the epidermis. Both Yap1 and Wwtr1 are localised in the nuclei of the peridermis and basal epidermis at the tailbud stage and at the 16-20 ss (Figure 2).…”