| China has the richest domestic duck breed resources, and the amount of duck rearing and consumption has been the top one in the world. In recent years，duck meat production has increased gradually, but still can’t completely meet the increasing consumer demand. The duck industry seemed to have a fine prospect, but it still have many problems, including low breeding technology and low meat production of duck individual. Now, these problems have greatly precluded the rapid development of meat duck industry. Therefore, it is very necessary to promote meat production of duck individual by advanced breeding and molecular technology.The insurmountable stage of poultry embryonic growth and development make great influence on the meat production of adults. It is one of the most effective measures to improve the individual’s meat production by promoting the growth and development of embryonic skeletal muscle. Because of the importance of poultry embryonic stage, two types of duck breeds (Gaoyou and Jinding duck breeds) with very different adult body weight and growth rate, were chose as experimental materials. After this research finished, it may explain the differences of embryonic growing and developing traits and the gene expressions of skeletal muscle development between the two duck breeds. Further more, we may know the effects of MRFs, CAPN3and extrinsic triiodothyronine (T3) on growth and development of skeletal muscle.Therefore, we would hope discover some genes associated with muscle mass of duck individual and provide some genetic methods of improving the production of duck meat in embryonic stage. The main findings are as follows:In order to study growth and development of embryo in Gaoyou duck and Jinding duck, embryo weight, embryo length, liver weight, breast muscle weight and leg muscle weight were tested and analyzed from13-day embryonic age to21-day embryonic age. Some important findings were showed as below:The atlas of duck embryonic growth and development was established by observed and recorded in the hatching process. Cumulative growth, absolute growth, relative growth and differential growth of the two duck breeds seemed the same. The testing performance of the two duck breeds increased gradually with the increase of embryonic age. The growth pressures of all traits had a trend of be strong in early stage and weak in later stage. Growth rate of each tissues and organs was inconsistent with that of embryo body. During the testing period, the growth rates of liver and leg muscle were smaller than that of embryo body, but that of breast muscle was larger. Also in this period, all of the five testing performance had no significant between Gaoyou duck and Jinding duck, but the embryo weight of Gaoyou duck was always heavier than Jinding duck’s. This research not only can provide scientific data for domestic duck incubation, but also can provide theoretical basis for the relative researches about duck embryo.The objective of this present study was to evaluate mRNA expression patterns of the four MRFs genes of MyoD1, MyoG, Myf6and Myf5in the skeletal muscle during early developmental stage of ducks. The mRNA expression levels of these four genes in the breast muscle and leg muscle at embryonic days13,17,21,25,27, as well as at1week post-hatching in Gaoyou and Jinding ducks were detected using quantitative RT-PCR method. The changing trend of mRNA expression of these four genes in same breed and tissue displayed almost the same. The mRNA expression of MyoG in both breeds showed highly significant negative correlation with embryo weight, breast muscle weight and leg muscle weight (P＜O.01).There were different mRNA expressions and their patterns of these four genes in different tissues. It indicated that each gene played different role in growth and development of breast muscle and leg muscle during embryonic stage.The myoblasts isolated from leg muscle and breast muscle in Gaoyou duck and Jinding duck at13-d,15-d,17-d,19-d,21-d and23-d embryonic age were cultured, respectively. Four MRFs genes of MyoD1, MyoG, Myf6and Myf5mRNA expressions in these myoblasts were detected by using quantitative RT-PCR method. One obvious feature was found that all of the genes’mRNA expressions in myoblasts from leg muscle and breast muscle at the17-d embryonic age were higher than the corresponding gene mRNA expressions at the other embryonic ages. There were different mRNA expressions and patterns of these four genes in different myoblasts. The four genes mRNA expressions in myoblast were higher than the expressions in relevant tissues.In order to investigate effects of extrinsic triiodothyronine (T3) on the growth and development of embryo and mRNA expression of three genes of MyoDl, Myf5and Myf6in duck sketelal myoblast., two methods of injecting T3diluted with saline solution into breeding eggs and adding T3into myoblast culturing medium were used in this study. The results displayed extrinsic T3can promote the growth and development of tissues and organisms in the embryonic development. But, different tissues had different reaction to T3. Body weights and breast muscle weights of the T3group were significantly higher than that of control group (P<0.05) at27-day embryonic age. The T3deposited in egg can accelerate the embryo growing and developing in a short time. After hatching, the duck body weight of T3injected group was lighter than control group’s, meanwhile, any other tissues in T3injected group displayed the trend of increasing first and then decreasing. Low density of T3can prompt mRNA expression of Myf5and Myf6in myoblast and high density of T3can obviously accelerate the mRNA expression of MyoD1in myoblast.In the present study, expression of CAPN3gene was quantified by RT-PCR in the breast and leg muscle tissues at days13,17,21,25,27of embryonic development, as well as at7days post-hatching (PH) in Gaoyou and Jinding ducks differing in growth rates. Meanwhile, the association between expression level of CAPN3gene and myofiber traits was also analyzed. The results showed that the CAPN3mRNA expression profile had a similar trend in both breeds and showed an extremely significant development differential diathesis. In breast muscle, the expression level of CAPN3mRNA was relatively low before25-d embryonic age and the lowest point appeared at21-d embryonic age, then increased significantly before hatching (embryonic27d) and7d PH. In leg muscle, the expression profile of CAPN3showed a "wave" trend, the expression peaking appeared at21-d embryonic age. Meanwhile varying degrees of linear correlation was found between CAPN3gene mRNA expression and myofiber types, diameter, cross-sectional area and density in duck, and in Jinding ducks, CAPN3gene mRNA expression was significantly correlated with myofiber diameter, cross-sectional area and density traits. These results suggested that CAPN3might have potential functions in controlling muscle fiber phenotype and development during embryonic and early post-hatching development in ducks. |
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