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Alpha-fetoprotein (AFP) is the major serum protein during development. AFP is one of the earliest proteins to be synthesised by the embryonic liver. The synthesis of AFP decreases dramatically after birth and only trace amounts are expressed in the adult liver. The tissue distribution of AFP in early human embryogenesis has not been defined. We have studied the expression pattern of AFP mRNA in human and mouse embryos by in situ hybridisation. In humans, AFP is expressed in the hepatic diverticulum at 26 d postovulation as it differentiates from the foregut endoderm (i.e. in the most primitive hepatocytes). It is also expressed in the endoderm of the gastrointestinal tract and in the yolk sac at this age. AFP is subsequently expressed in the mesonephros and transiently in the developing pancreas. In the mouse, no expression of AFP was observed in the mesonephros but other sites of expression were similar. Thus AFP has a distinct temporospatial expression pattern during the embryonic period and this differs between human and mouse species. It is interesting that AFP is expressed by tumours such as primitive gastrointestinal, renal cell and pancreatic tumours as well as those of hepatocyte origin. This distribution reflects the sites of AFP expression during development.

Turkey hens were fed either a standard breeder diet (CON, myristic acid, C14.0, 1.1%; palmitic acid, C16:0, 16.8%; oleic acid, C18:1, 23%; linoleic acid, C18:2, 48.7%) or a diet containing 5% coconut oil (COCO) enriched with medium chain fatty acids (MCFA; lauric acid, C12:0, 22.6%; C14:0, 10.8%; C16:0, 12.5%; C18:1, 14.8%; C18:2, 24.6%). After 10 d on the diets, fresh eggs were collected for yolk lipid and fatty acid (FA) determination. An additional 60 to 95 eggs were incubated and the FA profiles of the neutral lipid (NL) and phospholipid (PL) fractions of yolk sac and liver lipids were determined. The NL fraction of the yolk sac from CON eggs contained less C12:0 (0 vs 0.49%) and C14:0 (0.7 vs 4.6%) and more C18:1 (41.3 vs 37.5%). The PL fraction of the yolk sac from both treatments contained < 1% C14:0, and there was less than a 2% difference between treatments in other FA concentrations. The hepatic NL fraction from both treatments contained < 1% C14:0 and only C18:1 showed > 1% differences between treatments (Control = 59.9%; COCO = 56.62%). There were no dietary effects on the FA profile of hepatic PL. The presence of only minimal quantities of MCFA in hepatic NL and PL suggests that absorbed yolk sac MCFA are extensively metabolized during embryonic development.

Fatty acid (FA) profiles in embryonic yolk sacs (YS) and livers were studied in embryos from a randombred turkey line (RBC2) and a line selected for body weight at 16 wk (F line). There were no differences in FA profiles of fresh yolk lipids. During the course of incubation, oleic acid (C18:1) was higher and linoleic acid (C18:2) was lower in YS triglyceride (TG) and phospholipid (PL) subclasses in F line compared with RBC2 embryos. In both lines, the C18:1 content of YS cholesteryl esters (CE) increased from 58 to 63% during the last 6 d of incubation. From 22 to 28 d of incubation, there was a constant C18:1 concentration in hepatic CE, which was > 60% of total hepatic CE FA. As incubation proceeded, palmitic acid (C16:0) and C18:1 in hepatic TG decreased from 27 to 16% and 37 to 34%, respectively. The stearic acid (C18:0) in TG increased from 12% at Day 22 to 32% of total FA at hatch (Day 28) in RBC2 embryos compared with a lesser increase in the F line (11.8 to 18.6%). In hepatic PL, arachidonic acid (C20:4) decreased, whereas both C16:0 and C18:0 increased from 22 to 28 d of incubation. During this same time period, there was an overall decline in docosahexaenoic acid (C22:6) only in the RBC2. On Days 26 and 28, F line embryos had greater concentrations of C22:6 and C20:4 in hepatic PL than did RBC2. These results suggest that selection for increased BW has changed the proportional incorporation of different FA into embryonic lipids.

Carotenoid and retinol concentrations were determined in chicks hatched from carotenoid-enriched eggs while being fed a carotenoid free starter diet. Single Comb White Leghorn (SCWL) hatching eggs were obtained from breeder hens fed diets enriched with either 0.2% beta-carotene, canthaxanthin, lutein, or basal control. Twenty-five day-old chicks hatched from each treatment group were placed in a battery and fed a carotenoid-free basal diet. At 1, 4, 7, 10, and 13 d, five chicks per treatment were randomly selected, and blood serum, liver, and unabsorbed yolk sac were collected for carotenoid and retinol analysis. There were no significant differences in retinol concentrations in the serum, liver, and unabsorbed yolk sac of the chickens. Only small amounts of beta-carotene were detected in the chick tissues. Concentration of all three carotenoids and retinol were greater in the liver and unabsorbed yolk sac than in serum. In the serum and liver, respective carotenoid concentrations decreased and retinol concentration increased with increasing age, whereas respective carotenoid and retinol concentrations in the unabsorbed yolk sac increased over time. It may be concluded that yolk sac carotenoids are not absorbed well, as unabsorbed yolk sac concentrations increased over time, and that carotenoid in serum and liver decrease linearly with increasing age.

In two studies, changes in lipids and fatty acids from the yolk sac and liver of turkeys were determined during incubation and early postnatal growth. In Experiment 1, embryos were collected from Day 13 through 6 d posthatch. Embryos weighed 4.25 g at Day 13, 52.8 g at hatch (Day 28), and 104 g at 6 d. Total yolk lipid (grams per yolk sac) decreased from 9.48 g at Day 13 to 2.52 g at hatch (Day 28). Almost half (47%) of the yolk lipid decreased during the last week of incubation. In Experiment 2, embryos were collected daily from Day 22 through 2 d posthatch. Embryonic weight increased from 32.5 g at Day 22 to 55.8 g at hatch (Day 28), 3 g more than in Experiment 1. On Days 22 and 25, total yolk lipid (grams per yolk sac) was slightly less in Experiment 2 than in Experiment 1, but at hatch (Day 28) there were considerable differences (Experiment 1, 2.52 g; Experiment 2, 0.63 g), concomitant with increased hatch weight in Experiment 2. Liver DM percentage and ether extractable lipid increased as incubation proceeded. Oleic acid comprised the largest proportion of total yolk fatty acids and of liver fatty acids. There was a small but significant increase in yolk sac oleic acid (percentage of total fatty acids) between Day 22 (40%) and hatch (Day 28; 45.4%) and a much larger increase in liver oleic acid (46.6% to 56.5%). The absolute amount of all yolk sac fatty acids declined greatly during the second half of incubation through 6 d posthatch.

Lipid changes in the yolk sac of the embryo were studied in a randombred population of turkeys (RBC2) and a subline of the RBC2 selected for increased BW at 16 wk (F line). Comparisons of yolk sac and embryonic development were made between 22 d of incubation and hatch (28 d). Poults from the F line had heavier yolk sacs from 24 to 28 d and yolk free body weight was also heavier at hatch (61.1 vs 52.8 g). Yolk sac lipid (percentage of DM) declined faster in F line embryos (69 to 39%) compared with the RBC2 line (62 to 48%). In both lines, embryonic liver dry matter and lipids (percentage of DM) were similar. Yolk sac neutral lipids increased from 22 to 28 d (70 to 80% total lipid) in both lines and there was a concomitant decline in phospholipids (30 to 20%). The direction of the changes was similar for embryonic liver lipid. At 26 and 28 d, there were significantly increased neutral lipids (94 vs 88%) and decreased phospholipids (6 vs 12%) in RBC2 compared with F line embryonic livers. The concentration of cholesterol esters (percentage of total lipid) increased in the yolk sac and embryonic liver during the course of incubation. At 26 and 28 d, livers from RBC2 embryos had increased cholesterol ester concentration compared with livers from the F line.(ABSTRACT TRUNCATED AT 250 WORDS)