Yanchao Han

Congenital valve defects account for a substantial proportion of cardiovascular malformations, yet the molecular mechanisms orchestrating cardiac valve development remain incompletely elucidated. While Bone morphogenetic protein (BMP) signaling is essential for valvulogenesis, the specific contributions of individual BMP ligands, particularly the teleost-specific bmp16, have not been characterized. Using the CRISPR/Cas9 system, we generated a bmp16 null knockout and delineated critical roles of this ligand in valvular morphogenesis. bmp16 knockout embryos display a significant reduction in Sox9-positive valvular cells and exhibit severely dysplastic arterial valves, characterized by increased interleaflet distance, thickened leaflets, and shortened leaflet lengths. These morphological abnormalities correlate with impaired valve function, culminating in progressive blood regurgitation, ventricular dilation, and pericardial edema. Mechanistically, loss of bmp16 or pharmacological inhibition of BMP signaling significantly downregulates notch1b expression in developing valves, while pharmacological activation of Notch signaling rescues the regurgitation phenotype in bmp16 mutants. Collectively, our findings establish bmp16 as a novel regulator of valve development and uncover a functional BMP-Notch signaling axis required for vertebrate valvulogenesis, providing new insights into the molecular mechanisms that govern cardiac valve formation and pathogenesis.

Carnitine palmitoyltransferase 1 (CPT1) is a key regulatory enzyme in fatty acid metabolism, responsible for the translocation of long-chain fatty acids into the mitochondria for β-oxidation in diverse biological contexts. Recent studies implicated the critical role of cpt1 genes during zebrafish development and heart regeneration; however, a comprehensive characterization of their spatiotemporal expression dynamics remains lacking. Here, we systematically analyzed the expression profiles of four cpt1 paralogs ( cpt1aa , cpt1ab , cpt1b , and cpt1a2b ) during zebrafish embryogenesis and the expression of cpt1ab and cpt1b during zebrafish heart regeneration. Our results reveal that these paralogs exhibit distinct spatiotemporal expression patterns during zygotic development. While cpt1aa and cpt1ab share high sequence conservation (77%), their expression patterns diverge substantially. Conversely, cpt1ab and cpt1b display convergent cardiac and somitic expression despite lower sequence similarity (53%). Following ventricular ablation, cpt1b expression transiently ceased then recovered during regeneration, whereas cpt1ab remained unchanged. These findings shed light on the evolutionary conservation and functional divergence of cpt1 paralogs, which establish a critical foundation for elucidating paralog-specific roles in fatty acid metabolism during vertebrate development and regeneration.

Carnitine palmitoyltransferase 1b (Cpt1b) is a crucial rate-limiting enzyme in fatty acid metabolism, but its role and mechanism in early cardiac development remains unclear. Here, we show that cpt1b regulates cardiomyocyte proliferation during zebrafish development. Knocking out entire cpt1b coding sequences leads to impaired cardiomyocyte proliferation, while cardiomyocyte-specific overexpression of cpt1b promotes cardiomyocyte proliferation. RNA sequencing analysis and pharmacological studies identified glutamine synthetase as a key downstream effector of cpt1b in regulating cardiomyocyte proliferation. Our study elucidates a novel mechanism whereby cpt1b promotes zebrafish cardiomyocyte proliferation through glutamine synthetase, which provides new perspectives on the significance of fatty acid metabolism in heart development and the interplay between fatty acid and amino acid metabolic pathways.

Identification of signaling events that contribute to innate spinal cord regeneration in zebrafish can uncover new targets for modulating injury responses of the mammalian central nervous system. Using a chemical screen, we identify JNK signaling as a necessary regulator of glial cell cycling and tissue bridging during spinal cord regeneration in larval zebrafish. With a kinase translocation reporter, we visualize and quantify JNK signaling dynamics at single-cell resolution in glial cell populations in developing larvae and during injury-induced regeneration. Glial JNK signaling is patterned in time and space during development and regeneration, decreasing globally as the tissue matures and increasing in the rostral cord stump upon transection injury. Thus, dynamic and regional regulation of JNK signaling help to direct glial cell behaviors during innate spinal cord regeneration.

The lineage and developmental trajectory of a cell are key determinants of cellular identity. In the vascular system, endothelial cells (ECs) of blood and lymphatic vessels differentiate and specialize to cater to the unique physiological demands of each organ^1,2. Although lymphatic vessels were shown to derive from multiple cellular origins, lymphatic ECs (LECs) are not known to generate other cell types^3,4. Here we use recurrent imaging and lineage-tracing of ECs in zebrafish anal fins, from early development to adulthood, to uncover a mechanism of specialized blood vessel formation through the transdifferentiation of LECs. Moreover, we demonstrate that deriving anal-fin vessels from lymphatic versus blood ECs results in functional differences in the adult organism, uncovering a link between cell ontogeny and functionality. We further use single-cell RNA-sequencing analysis to characterize the different cellular populations and transition states involved in the transdifferentiation process. Finally, we show that, similar to normal development, the vasculature is rederived from lymphatics during anal-fin regeneration, demonstrating that LECs in adult fish retain both potency and plasticity for generating blood ECs. Overall, our research highlights an innate mechanism of blood vessel formation through LEC transdifferentiation, and provides in vivo evidence for a link between cell ontogeny and functionality in ECs.