Cysteine and Aspartic Proteases Underlie the Digestion of Egg Yolk Proteins during the Development of Columba livia domestica Embryo

Yolk proteins undergo digestion either inside the egg yolk or in the surrounding yolk sac membrane (YSM) before being consumed by the developing avian embryo. However, the mechanisms underlying the digestion of yolk proteins during embryogenesis are largely unexplored in the pigeon Columba livia domestica. To better understand these mechanisms, the present study examined the classes of activated proteases in the egg yolk and the gene expression patterns of cathepsin B (CTSB) and cathepsin D (CTSD), which encode for lysosomal cysteine and aspartic proteases, respectively, in the YSM. We investigated the activated proteases by applying different types of protease inhibitors to yolk samples taken from incubation day 16. Then, we detected the mRNA levels of CTSB and CTSD in the YSM at incubation days 6, 8, 10, and 12-17. Both cysteine and aspartic proteases appeared to be activated in the egg yolk. Moreover, CTSB expression increased progressively and reached the maximum value on day 13; however, it decreased significantly on days 14 and 15 and further reduced toward hatching (day 17). In contrast, CTSD expression was weak and fluctuated insignificantly during development. Our results suggest that the degradation of yolk proteins at late developmental stages largely occurs in the egg yolk itself, probably by the activated cysteine and aspartic proteases. Furthermore, cathepsin B in the YSM seems to have a primary role in protein digestion, but this role decreases toward hatching.(AU)

Effect of Feeding Low-Oil Ddgs to Laying Hens and Broiler Chickens on Performance and Egg Yolk and Skin Pigmentation

Two experiments were conducted to evaluate the nutritional quality of two sources of low-oil distiller's dried grains with solubles (DDGS) and their pigmenting ability for broiler chicken skin and egg yolks. In Experiment 1, 360 Bovan-White hens between 69 and 77 weeks of age were randomly assigned to five dietary treatments with 6 replicates of 12 hens each. In Experiment 2, 375 Ross 308 broiler chickens were randomly assigned to five treatments with three replicates of 25 birds each. The chickens were fed the experimental diets from one to 42 d of age. In both experiments, treatments consisted of a basal diet with no DDGS, and diets with 6% or 12% inclusion of DDGS from two sources. In Experiment 1, no significant differences in performance were detected among treatments (p> 0.05). Egg yolk pigmentation, according to CR-400 Minolta Colorimeter redness (a) and yellowness (b), linearly increased (p 0.05) with DDGS inclusions. In Experiment 2, no significant differences (p>0.05) were detected among treatments in growth performance, carcass yield, or abdominal fat at 42 d of age. Yellowness linearly increased (p 0.05) in the skin and abdominal fat of the birds that consumed diets with DDGS. The results of the current study indicate that feeding two sources of low-oil DDGS to broiler chicks or laying hens does not negatively affect egg production or growth performance while improves egg yolk and skin yellowness.(AU)

Effect of Feeding Low-Oil Ddgs to Laying Hens and Broiler Chickens on Performance and Egg Yolk and Skin Pigmentation

Two experiments were conducted to evaluate the nutritional quality of two sources of low-oil distiller's dried grains with solubles (DDGS) and their pigmenting ability for broiler chicken skin and egg yolks. In Experiment 1, 360 Bovan-White hens between 69 and 77 weeks of age were randomly assigned to five dietary treatments with 6 replicates of 12 hens each. In Experiment 2, 375 Ross 308 broiler chickens were randomly assigned to five treatments with three replicates of 25 birds each. The chickens were fed the experimental diets from one to 42 d of age. In both experiments, treatments consisted of a basal diet with no DDGS, and diets with 6% or 12% inclusion of DDGS from two sources. In Experiment 1, no significant differences in performance were detected among treatments (p> 0.05). Egg yolk pigmentation, according to CR-400 Minolta Colorimeter redness (a) and yellowness (b), linearly increased (p 0.05) with DDGS inclusions. In Experiment 2, no significant differences (p>0.05) were detected among treatments in growth performance, carcass yield, or abdominal fat at 42 d of age. Yellowness linearly increased (p 0.05) in the skin and abdominal fat of the birds that consumed diets with DDGS. The results of the current study indicate that feeding two sources of low-oil DDGS to broiler chicks or laying hens does not negatively affect egg production or growth performance while improves egg yolk and skin yellowness.

Gema do ovo de galinha e a ação protetora de suas lipoproteínas de baixa densidade na criopreservação do sêmen: uma revisão / Hens egg yolk and the protective action of its low density lipoproteins on semen cryopreservation: a review

Desde 1939, a gema do ovo tem sido utilizada na biotecnologia da reprodução como ingrediente essencial nos meios diluidores para resfriamento e congelamento de espermatozoides em várias espécies domésticas. A gema é formada por lipoproteínas, livetinas e fosvitinas, encontradas em duas frações facilmente separáveis pelo método de centrifugação: o grânulo e o plasma. Acredita-se que as lipoproteínas de baixa densidade, presentes no plasma, sejam as responsáveis por sua ação crioprotetora. Esta revisão enfoca a composição química do ovo de galinha e de sua gema, mostrando, cronologicamente, como foram desenvolvidas as hipóteses existentes sobre seu mecanismo de ação no congelamento de sêmen.(AU)

Since 1939, the hens egg yolk has been used as an essential ingredient in extenders for cooling and freezing sperm of several domestic species, in reproductive biotechnology protocols. The egg yolk is composed of lipoproteins, livetins, and lipovitins. These components can be easily separated by centrifugation in the granular and the plasmatic fractions. It has been acknowledged that the low density lipoproteins present in the plasma are responsible for the protective effects of the egg yolk. This review focuses on the chemical compound of the egg yolk and historical aspects of the hypotheses that try to explain the mechanism of action of the egg yolk on sperm cryopreservation. (AU)

Gema do ovo de galinha e a ação protetora de suas lipoproteínas de baixa densidade na criopreservação do sêmen: uma revisão / Hen’s egg yolk and the protective action of its low density lipoproteins on semen cryopreservation: a review

Desde 1939, a gema do ovo tem sido utilizada na biotecnologia da reprodução como ingrediente essencial nos meios diluidores para resfriamento e congelamento de espermatozoides em várias espécies domésticas. A gema é formada por lipoproteínas, livetinas e fosvitinas, encontradas em duas frações facilmente separáveis pelo método de centrifugação: o grânulo e o plasma. Acredita-se que as lipoproteínas de baixa densidade, presentes no plasma, sejam as responsáveis por sua ação crioprotetora. Esta revisão enfoca a composição química do ovo de galinha e de sua gema, mostrando, cronologicamente, como foram desenvolvidas as hipóteses existentes sobre seu mecanismo de ação no congelamento de sêmen.

Since 1939, the hen’s egg yolk has been used as an essential ingredient in extenders for cooling and freezing sperm of several domestic species, in reproductive biotechnology protocols. The egg yolk is composed of lipoproteins, livetins, and lipovitins. These components can be easily separated by centrifugation in the granular and the plasmatic fractions. It has been acknowledged that the low density lipoproteins present in the plasma are responsible for the protective effects of the egg yolk. This review focuses on the chemical compound of the egg yolk and historical aspects of the hypotheses that try to explain the mechanism of action of the egg yolk on sperm cryopreservation.

Inorganic polyphosphate inhibits an aspartic protease-like activity in the eggs of Rhodnius prolixus (Stahl) and impairs yolk mobilization in vitro.

Inorganic polyphosphate (poly P) is a polymer of phosphate residues that has been shown to act as modulator of some vertebrate cathepsins. In the egg yolk granules of Rhodnius prolixus, a cathepsin D is the main protease involved in yolk mobilization and is dependent on an activation by acid phosphatases. In this study, we showed a possible role of poly P stored inside yolk granules on the inhibition of cathepsin D and arrest of yolk mobilization during early embryogenesis of these insects. Enzymatic assays detected poly P stores inside the eggs of R. prolixus. We observed that micromolar poly P concentrations inhibited cathepsin D proteolytic activity using both synthetic peptides and homogenates of egg yolk as substrates. Poly P was a substrate for Rhodnius acid phosphatase and also a strong competitive inhibitor of a pNPPase activity. Fusion events have been suggested as important steps towards acid phosphatase transport to yolk granules. We observed that poly P levels in those compartments were reduced after in vitro fusion assays and that the remaining poly P did not have the same cathepsin D inhibition activity after fusion. Our results are consistent with the hypothesis that poly P is a cathepsin D inhibitor and a substrate for acid phosphatase inside yolk granules. It is possible that, once activated, acid phosphatase might degrade poly P, allowing cathepsin D to initiate yolk proteolysis. We, therefore, suggest that degradation of poly P might represent a new step toward yolk mobilization during embryogenesis of R. prolixus.