The Functional Study Of Gnal3 And Lrp8 In Zebrafish Embryogenesis

Heterotrimeric guanine nucleotide-binding proteins (G proteins) function as signal transducers and control many different physiologic processes. G proteins can be grouped into four families Gs, Gi, Gq and G12. Gα13,with its gene name gan13,belongs to the G12 family. The Ga13(?)mouse embryos have defective vascular systems and display embryonic lethality (-E9.5), but the molecular basis that underlies the vascular defect observed in Gα13(?) mouse embryos has not been defined. In zebrafish, there are two isoforms of Gα13:Gα13a and Gα13b. During zebrafish gastrulation, Ga12/13 are required for convergence and extension (CE) movements. Ga12/13 might regulate epiboly through two distinct mechanisms by limiting E-cadherin activity and modulating the organization of the actin cytoskeleton. We show here that knockdown of Gα13 in zebrafish results in hematopoietic and angiogenic defects. The Gα13b morphants show complete loss of blood circulation. The expression of hematopoietic and angiogenic markers such as gata1,pu.l,flk were also lost. Further studies reveal that blood cells and vascular endothelial cells have undergone apoptosis through a p>53-dependent pathway in Gα13b-depleted embryos. Injection of p53 morpholino could partially rescue the phenotype of Ga13b morphants and restore the expression of hematopietic and angiogenic markers. These data demonstrate a new role for Gα13 in cell survival. Lrp8 belongs to the low-density lipoprotein receptor super family. The sequence of Irp8 homology in zebrafish was predicted based on the genomic sequences and has not verified by experiments. In this study, we firstly cloned its cDNA and found our sequence with an additional 57bp fragment to the predicted one. During the late segmentation, lrp8 specifically expresses in four groups of cells in the rhombomere. Its signals can also be detected throughout the surface of yolk sac as presented in pairs of spots. In the embryos of 2dpf or older, Irp8 expresses highly in the centre nerve system, especially in the middle line of the brain. Further study revealed that the lost of Irp8 would suppress the myelination as well as axon growth. All these results will contribute to further study of the molecular mechanism under this process.