Increased Yolk Lipid Mobilization Promotes Zebrafish Post-Segmentation Growth via an Hnf4-Lipoprotein Axis

In egg-laying animals, all maternal nutrients are sealed within the yolk, creating a closed system ideal for addressing this question. Using zebrafish, we tracked the mobilization of the two principal yolk reserves, proteins and lipids, throughout development.

Protein catabolism proceeds continuously from cleavage to hatching, whereas large-scale lipid mobilization is postponed until after segmentation. This lipid switch is initiated by zygotic activation of the transcription factors Hnf4a/b, which induce the acidic lipase Pla2g15 to hydrolyze lipids stored in yolk granules. The released lipids are subsequently transferred to the yolk-syncytial-layer endoplasmic reticulum, packaged into lipoproteins, and transported through the circulation to distant tissues.