Axon guidance genes control hepatic artery development.

Earlier data on liver development demonstrated that morphogenesis of the bile duct, portal mesenchyme and hepatic artery is interdependent, yet how this interdependency is orchestrated remains unknown. Here, using 2D and 3D imaging, we first describe how portal mesenchymal cells become organised to form hepatic arteries. Next, we examined intercellular signalling active during portal area development and found that axon guidance genes are dynamically expressed in developing bile ducts and portal mesenchyme. Using tissue-specific gene inactivation in mice, we show that the repulsive guidance molecule BMP co-receptor A (RGMA)/neogenin (NEO1) receptor/ligand pair is dispensable for portal area development, but that deficient roundabout 2 (ROBO2)/SLIT2 signalling in the portal mesenchyme causes reduced maturation of the vascular smooth muscle cells that form the tunica media of the hepatic artery. This arterial anomaly does not impact liver function in homeostatic conditions, but is associated with significant tissular damage following partial hepatectomy. In conclusion, our work identifies new players in development of the liver vasculature in health and liver regeneration.

Oxidative stress differentially impacts male and female bovine embryos depending on the culture medium and the stress condition.

Male and female embryos are known to differ for their metabolism and response to environmental factors very early in development. The present study aimed to evaluate the response to oxidative stress of male and female bovine embryos at the morula-blastocyst stages in terms of developmental rates, total cell number and apoptotic rates in two culture conditions. Embryos where cultured in a medium supplemented with either 5% fetal calf serum (FCS) or 4 mg/mL bovine serum albumin and a mixture of insulin, transferrin and selenium (BSA-ITS). Oxidative stress was applied at Day-5 post insemination (pi) by adding either AAPH or menadione to the culture medium, and blastocysts were analyzed at Day-7pi. The impact on development and blastocyst quality was dependent on the culture medium and the stress inducer but differed between male and female embryos. Male embryos resisted better to oxidative stress in FCS supplemented medium, no matter the stress inducer. Accordingly, the impact on blastocyst cell number tended to be higher in female blastocysts after stress induction with AAPH in FCS supplemented medium. On the other hand, in BSA-ITS supplemented medium, female embryos were more resistant to AAPH induced stress, while menadione had no impact on sex ratio. The weaker resistance of males to AAPH in this medium is in accordance with their trend to show a higher increase in apoptotic rates than females in this condition. In conclusion, this study shows that oxidative stress has differential impact on male and female bovine blastocysts depending on the culture condition and on the way oxidative stress is induced.