Akt is believed to be important for vascular development, but complex tissue-specific loss-of-function studies have been difficult in mice because of embryonic lethality. In a new study, Wenping Zhou, Joey Ghersi, Stefania Nicoli and colleagues report the phenotype of a complete Akt mutant zebrafish and its role in arterial specification via Notch signaling. To learn more about their work, we spoke with corresponding authors Joey Ghersi, Assistant Professor at Centre Hospitalier Universitaire (CHU) Sainte-Justine, Canada, and Stefania Nicoli, Associate Professor Tenure at Yale University, USA.

Joey Ghersi (left) and Stefania Nicoli (right)

Stefania, what are the questions your lab is trying to answer?

SN: In our lab, we study the vascular system to understand how cells respond to both micro and macro environmental perturbations. We focus on developing embryos because it is during this stage that cells, tissues and organs first learn to adapt to environmental changes, including organ-specific behaviors. For instance, artery specification is a crucial and complex endothelial cell behavior, and its disruption can increase the risk of various diseases. By studying how these behaviors are acquired during embryogenesis, we aim to create a blueprint for identifying early signs of disease development.

Joey, how did you come to work in the lab and what drives your research today?

JG: My journey into this field began during my PhD in developmental hematopoiesis at Julien Bertrand's laboratory in Geneva, Switzerland. There, I recognized the need to expand my expertise in vascular development due to the close relationship between hematopoietic and vascular tissues. I was drawn to the Nicoli laboratory, an impactful lab in vascular biology, as it offered the perfect opportunity to deepen my understanding of these interconnected systems. My research has consistently focused on how cells determine their fate and form specific tissues, with a particular fascination for the interplay between vascular and hematopoietic cells throughout development and life. Today, I am driven to unravel the molecular mechanisms governing the transition from endothelial to hematopoietic cells, aiming to contribute to our understanding of blood disorders and potential therapeutic strategies in regenerative medicine.

Tell us about the background of the field that inspired your work

JG: The field of vascular development in vertebrates is centered on the formation of the two primary vessels, the artery and the vein, that originate from a common progenitor that differentiates in response to specific cellular cues. While it is well established that VEGF and Notch signaling pathways are crucial in this cell fate decision, our understanding of the key protein kinases involved remains limited. Akt, a protein kinase that interacts with both VEGF and Notch pathways, presents an intriguing area for exploration; however, most studies have focused on single Akt isoforms, leaving significant gaps in our knowledge. Our research, initiated and significantly advanced by Dr Wenping Zhou during her time at Yale, aims to address this gap by developing a complete knockout model of Akt expression in zebrafish, allowing us to investigate the comprehensive effects of Akt loss on vascular formation. By elucidating the role of Akt in this process, we hope to enhance our understanding of the complex signaling interactions that govern artery and vein differentiation, with potential implications for both developmental biology and vascular-related diseases. I would like to acknowledge Dr Wenping Zhou, the co-first author, whose vision and foundational work were crucial to this project. Her early contributions laid the groundwork for this significant advancement in the field of vascular development.

Model of artery specification controlled by Rtk/Akt/Notch signaling

Model of artery specification controlled by Rtk/Akt/Notch signaling

Can you give us the key results of the paper in a paragraph?

SN & JG: This study presents a previously unreported zebrafish model with complete mutations in all four zebrafish Akt isoforms, offering unique insights into Akt's role in vascular development. Unlike mouse models, where the loss of Akt isoforms is lethal during early development, these zebrafish embryos survive to later developmental stages, enabling a new analysis of Akt's functions. For instance, we discovered that Akt signaling is essential for the proper specification of arterial cells during the formation of the first embryonic vessel: the aorta. Through a combination of time-lapse imaging, single-cell RNA sequencing and cell type-specific constructs, the study identified Notch signaling as the primary pathway affected by Akt loss of function. Specifically, in the absence of Akt activity, arterial cells exhibited decreased Notch signaling, resulting in impaired arterial program activation. This finding establishes Akt as a mediator in the arterial specification process, acting upstream of Notch signaling. The study not only elucidates the molecular mechanisms underlying arteriovenous differentiation but also highlights the potential of this zebrafish model for further investigations into Akt's roles in development and disease.

Why did you choose to submit this paper to Development?

JG: Development is one of the leading journals in the field of developmental biology, known for its rigorous standards and impactful publications. Actually, my first research article was published in Development, and I have always valued the journal's commitment to scientific integrity and excellence. Additionally, Development has a strong focus on advances in zebrafish biology, as well as vascular and hematopoietic development, making it the ideal platform to showcase our findings.

Joey, what is next for you after this paper?

JG: I've recently transitioned from Stefania Nicoli's laboratory to establish my own research group at the CHU Sainte-Justine and the University of Montreal in Canada. This marks an exciting new chapter in my career. My lab is focusing on unraveling the mechanisms by which cell signaling in endothelial cells drives hematopoietic stem and progenitor cell heterogeneity. For those interested in following our work or potential collaborations, I invite you to visit our lab website at ghersilab.com, where we share our ongoing projects and future research directions.

Finally, let's move outside the lab – what do you like to do in your spare time?

JG: I am passionate about nature photography. This love for capturing nature is perhaps why I enjoy spending so much time in the confocal room. Recently, I've also discovered the joy of biking around Montreal. It's a great way to stay active and explore new places while giving me time to think.

J.G.: Centre Hospitalier Universitaire, Sainte-Justine Research Center, Montréal, QC, Canada; Department of Pathology and Cell Biology, Faculty of Medicine, Université de Montréal, Montréal, QC, Canada.

S.N.: Department of Pharmacology, Yale University School of Medicine, New Haven, CT 06510, USA.

J.G. & S.N.: Vascular Biology & Therapeutics Program, Yale Cardiovascular Research Center, and Department of Internal Medicine (Section of Cardiology), Yale University School of Medicine, New Haven, CT 06510, USA.

E-mail: [email protected]; [email protected]

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Akt is a mediator of artery specification during zebrafish development
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Development
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