Mechanical forces in avian embryo development.

Research using avian embryos has led to major conceptual advances in developmental biology, virology, immunology, genetics and cell biology. The avian embryo has several significant advantages, including ready availability and ease of accessibility, rapid development with marked similarities to mammals and a high amenability to manipulation. As mechanical forces are increasingly recognised as key drivers of morphogenesis, this powerful model system is shedding new light on the mechanobiology of embryonic development. Here, we highlight progress in understanding how mechanical forces direct key morphogenetic processes in the early avian embryo. Recent advances in quantitative live imaging and modelling are elaborating upon traditional work using physical models and embryo manipulations to reveal cell dynamics and tissue forces in ever greater detail. The recent application of transgenic technologies further increases the strength of the avian model and is providing important insights about previously intractable developmental processes.

Selenium toxicity in breeding ring-necked pheasants (Phasianus colchicus).

A flock of breeding ring-necked pheasants received feed with a high selenium content. Within 4 days of eating the toxic feed, the rate of egg production began to decrease, and bird aggression increased. Approximately 12% of the hens died within a week. Necropsy of the hens revealed colorless fluid around the heart and a friable, but otherwise normal, liver. The rapid onset of the problem and signs noted at necropsy suggested toxicosis. Based on analysis, the feed contained 9.3 ppm of selenium. Selenium toxicity was consistent with the histologic diagnosis of degenerative cardiomyopathy, vacuolar degeneration of hepatocytes, and centrilobular hepatic necrosis. After 8 days, the toxic feed was removed and replaced with fresh feed. Egg production, which had dropped to 50%, returned to normal within 10 days of feed replacement. Hatchability of eggs laid from days 8 to 14 after delivery of the toxic feed was 35%. Approximately 10% of the chicks that hatched had deformed beaks and abnormal eyes. Many of the chicks that died in the shell had deformities, bringing the total to more than 50% of all embryos that developed. The selenium content of eggs that had no embryonic development was 2.05 ppm. Hatchability of eggs laid from days 21 to 28 after the toxic feed was delivered was almost 80%, which was slightly lower than normal. The selenium content of these eggs was 0.30 ppm. These results show the rapid onset and correction of selenium toxicity and suggest that specific embryologic defects are diagnostic for selenium toxicity.

Yolk lipids of developing atherosclerosis susceptible White Carneau and atherosclerosis resistant Show Racer pigeon embryos.

The lipid composition of yolks of developing embryonic atherosclerosis-susceptible White Carneau (WC) and -resistant Show Racer (SR) pigeons was analyzed to determine whether embryonic nutrition might be a factor in the difference in susceptibility to aortic atherosclerosis. The yolks of 1-day and 18-day old embryos were analyzed, and the amounts of phospholipid, sterol, non-esterified fatty acid, triglyceride, cholesteryl ester, and hydrocarbon were determined. On the first day of development in both breeds, triglycerides composed 80% of the total lipid content of the yolk; phospholipids, cholesteryl ester, sterols and non-esterified fatty acids comprised the rest. There was no difference between breeds in the amount of lipid in each class or in the total lipid. Therefore, the initial lipid diet of these embryos is not a factor in development of the disease. Examination of the yolk just prior to hatching, revealed that in both breeds there was a significant decrease in total yolk lipids, but unequal utilization of lipid constitutents between breeds. Significantly higher amounts of phospholipids remained in the yolk of the WC pigeons. During embryogenesis, the SR pigeons consumed significantly more of each lipid than the atherosclerosis-susceptible breed. This may indicate that there is a difference between the two breeds in lipid metabolism.