Biology subjects

Derrick, C. J.

Publications and source records attributed to Derrick, C. J..

5 recordsLinked to original sources

bioRxiv2025

Remodelling of supernumerary leaflet primordia leads to bicuspid aortic valve (BAV) caused by loss of primary cilia

AimsBicuspid aortic valve (BAV), where two valve leaflets are found instead of the usual three, affects 1-2% of the general population and is associated with significant morbidity and mortality. Despite its frequency, the majority of cases remain unexplained. This is, at least in part, because there are two types of valve leaflet primordia: endocardial cushions and intercalated valve swellings (ICVS). Moreover, multiple progenitors make distinct contribution to the formation of these primordia. Genomic studies in mouse and human have suggested a correlation between BAV and malfunctional primary cilia. However, the precise requirement for cilia during early embryonic valvulogenesis remains unknown. Methods and resultsHere, we disrupted primary cilia by deleting the ciliary gene Ift88 in the main progenitor cells forming the aortic valve using specific Cre drivers: Wnt1-Cre for neural crest cells, Isl1-Cre for second heart field cells (SHF); Tie2-Cre for endocardial-derived cells and Tnnt2-Cre for direct-differentiating SHF in the ICVS. Loss of Ift88, and thus primary cilia, from neural crest cells and endocardium did not impact aortic valve formation. However, primary cilia are essential in SHF cells for aortic valve leaflet formation, with over half of Ift88f/f;Isl1-Cre mutants presenting with BAV. As the valve leaflets are forming, 50% of the Ift88f/f;Isl1-Cre mutants have two small leaflets in the position of the usual posterior leaflet, meaning that at this stage the aortic valve is quadricuspid, which then remodels to BAV by E15.5. Mechanistic studies demonstrate premature differentiation of SHF cells as the ICVS form, leading to the formation of a broadened ICVS that forms two posterior leaflet precursors. This abnormality in the formation of the ICVS is associated with disruption of Notch-Jag1 signalling pathway, with Jag1f/f;Isl1-Cre mutants presenting with a similar phenotype. ConclusionsThese data show that primary cilia, via the Notch-Jag1 signalling pathway, regulate differentiation of SHF cells in the aortic valve primordia. Additionally, we identify a mechanistic link between the developmental basis of quadricuspid and bicuspid arterial valve leaflets. Translational PerspectiveSeveral genomic studies in human and mouse have suggested that disruption of cilia-related genes may be a significant cause of CHD. Although there is limited data from animal models to suggest a link between cilia and bicuspid aortic valve (BAV), the mechanisms underpinning BAV formation during early valvulogenesis have not been described. Here, we established a potential mechanism underpinning BAV formation, highlighting a role for primary cilia in a subset of valve interstitial cells (VIC) derived from second heart field progenitors. Loss of cilia altered VIC differentiation and valvulogenesis. This study confirms that disruption of cilial formation and/or function can lead to arterial valve defects and could pave the way to finding therapies for patient benefit.

developmental biology↗

bioRxiv2024

Zebrafish arterial valve development occurs through direct differentiation of second heart field progenitors

AimsBicuspid Aortic Valve (BAV) is the most common congenital heart defect, affecting at least 2% of the population. The embryonic origins of BAV remain poorly understood, limiting the identification of assays for validating patient variants and ultimately causative genes for BAV. In both human and mouse, the left and right leaflets of the arterial valves arise from the outflow tract cushions, with interstitial cells originating from neural crest cells and endocardial-to-mesenchymal transition (EndoMT). In contrast, an EndoMT-independent mechanism of direct differentiation by cardiac progenitors from the second heart field (SHF) is responsible for the formation of the anterior and posterior leaflets. Defects in either of these developmental mechanisms can result in BAV. Although zebrafish have been suggested as a model for human variant testing, their naturally bicuspid arterial valve has not been considered suitable for understanding human arterial valve development. Here, we have set out to investigate to what extent the processes involved in arterial valve development are conserved in zebrafish and ultimately, whether functional testing of BAV variants could be carried out in zebrafish. Methods and ResultsUsing a combination of live imaging, immunohistochemistry and Cre-mediated lineage tracing, we show that the zebrafish arterial valve primordia develop directly from undifferentiated SHF progenitors with no contribution from EndoMT or neural crest, in keeping with the human and mouse anterior and posterior leaflets. Moreover, once formed, these primordia share common subsequent developmental events with all three mammalian arterial valve leaflets. ConclusionsOur work highlights a conserved ancestral mechanism of arterial leaflet formation from the SHF and identifies that development of the zebrafish arterial valve is distinct from that of the atrioventricular valve. Crucially, this confirms the utility of zebrafish for understanding the development of specific BAV subtypes and arterial valve dysplasia, offering potential for high-throughput variant testing. Translational PerspectiveLarge genomic studies of patients with Bicuspid Aortic Valve (BAV) have identified numerous variants predicted to be causative, yet due to a lack of suitable, in vivo functional assays, advancement of genetic testing, discussion of risk to family members and accurate prognosis is not yet widely possible. Here, we show that zebrafish demonstrate a high level of conservation in arterial valve development with the intercalated leaflets in human, establishing zebrafish as a suitable in vivo model that can begin to overcome the disconnect between clinical genetics and developmental biology.

developmental biology↗

bioRxiv2023

Llgl1 mediates timely epicardial emergence and establishment of an apical laminin sheath around the trabeculating cardiac ventricle.

During heart development, the embryonic ventricle becomes enveloped by the epicardium, a layer of mesothelium which adheres to the outer apical surface of the heart. This is concomitant with onset of ventricular trabeculation, where a subset of cardiomyocytes lose apicobasal polarity and delaminate basally from the ventricular wall, projecting into the cardiac lumen to begin building the muscle mass necessary for adult cardiac function. Lethal(2) giant larvae homolog 1 (Llgl1) regulates the formation of apical cell junctions and apicobasal polarity, and we investigated its role in ventricular wall maturation, including trabeculation and epicardial establishment. We found that llgl1 mutant zebrafish embryos exhibit aberrantly positioned cardiomyocytes during early trabeculation, some of which extrude apically into the pericardial space. While investigating apical cardiomyocyte extrusion we identified a basal to apical shift in laminin deposition in the ventricular wall. Initially laminin deposition occurs on the luminal (basal) surface of the heart but concomitant with the onset of trabeculation basal laminin is removed and is instead deposited on the exterior (apical) surface of the ventricle. We find that epicardial cells express several laminin subunits as they adhere to the ventricular wall, and show that the epicardium is required for laminin deposition on the ventricular surface. In llgl1 mutants the timing of the basal-apical laminin shift is delayed, in line with a delay in establishment of the epicardial layer. Analysis of earlier epicardial development reveals that while both Llgl1 and laminin are not required for specification of the proepicardial organ, they are instead required for dissemination of epicardial cells to the ventricular surface. Together our analyses reveal an unexpected role for Llgl1 in correct timing of epicardial development, supporting integrity of the myocardial wall during early trabeculation.

developmental biology↗

bioRxiv2021

Lamb1a regulates atrial growth by limiting excessive, contractility-dependent second heart field addition during zebrafish heart development

During early vertebrate heart development, the heart transitions from a linear tube to a complex asymmetric structure. This process includes looping of the tube and ballooning of the emerging cardiac chambers, which occur simultaneously with growth of the heart. A key driver of cardiac growth is deployment of cells from the Second Heart Field (SHF) into both poles of the heart, with cardiac morphogenesis and growth intimately linked in heart development. Laminin is a core component of extracellular matrix (ECM) basement membranes, and although mutations in specific laminin subunits are linked with a variety of cardiac abnormalities, including congenital heart disease and dilated cardiomyopathy, no role for laminin has been identified in early vertebrate heart morphogenesis. We identified dynamic, tissue-specific expression of laminin subunit genes in the developing zebrafish heart, supporting a role for laminins in heart morphogenesis. lamb1a mutants exhibit cardiomegaly from 2dpf onwards, with subsequent progressive defects in cardiac morphogenesis characterised by a failure of the chambers to compact around the developing atrioventricular canal. We show that loss of lamb1a results in excess addition of SHF cells to the atrium, revealing that Lamb1a functions to limit heart size during cardiac development by restricting SHF addition to the venous pole. lamb1a mutants exhibit hallmarks of altered haemodynamics, and specifically blocking cardiac contractility in lamb1a mutants rescues heart size and atrial SHF addition. Furthermore, we identify that FGF and RA signalling, two conserved pathways promoting SHF addition, are regulated by heart contractility and are dysregulated in lamb1a mutants, suggesting that laminin mediates interactions between SHF deployment, heart biomechanics, and biochemical signalling during heart development. Together, this describes the first requirement for laminins in early vertebrate heart morphogenesis, reinforcing the importance of specialised ECM composition in cardiac development.

developmental biology↗

bioRxiv2019

Asymmetric Hapln1a drives regionalised cardiac ECM expansion and promotes heart morphogenesis during zebrafish development

The mature vertebrate heart develops from a simple linear cardiac tube during early development through a series of highly asymmetric morphogenetic processes including cardiac looping and chamber ballooning. While the directionality of heart morphogenesis is partly controlled by embryonic laterality signals, previous studies have suggested that these extrinsic laterality cues interact with tissue-intrinsic signals in the heart to ensure robust asymmetric cardiac morphogenesis. Using live in vivo imaging of zebrafish embryos we describe a left-sided, chamber-specific expansion of the extracellular matrix (ECM) between the myocardium and endocardium at early stages of heart morphogenesis. We use Tomo-seq, a spatial transcriptomic approach, to identify transient and regionalised expression of hyaluronan and proteoglycan link protein 1a (hapln1a), encoding an ECM cross-linking protein, in the heart tube prior to cardiac looping overlapping with regionalised ECM expansion. Loss- and gain-of-function experiments demonstrate that regionalised Hapln1a promotes heart morphogenesis through regional modulation of ECM thickness in the heart tube. Finally, we show that while induction of asymmetric hapln1a expression is independent of embryonic left-right asymmetry, these laterality cues are required to orient the hapln1a-expressing cells asymmetrically along the left-right axis of the heart tube. Together, we propose a model whereby laterality cues position hapln1a expression on the left of the heart tube, and this asymmetric Hapln1a deposition drives ECM asymmetry and subsequently promotes robust asymmetric cardiac morphogenesis.

developmental biology↗