الفهرس 
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Abstract
Chickens are source of high quality animal protein. Flesh of the native breeds of chickens is an important component of the Egyptian diet. Skeletal muscle is the edible part of the chickens and it is a tissue of major economic importance for meat production and so understanding the growth and development of skeletal muscle is one of the most important goals in meat production science. Since there are no studies focusing on histomorphology and the molecular basis of skeletal muscle development in Egyptian native chickens, the aim of this study is to investigate the histomorphology and expression pattern of the growth related genes MyoD, IGF1 and Fol in skeletal muscles during pre-hatching developmental stages and at one day old chick in El-Salam strain of chicken.
The objectives of the present study were to
1) Study the histomorphological structure of the skeletal muscle during pre-hatching stages(D2-D5).This was performed using light and scanning electron microscopes.
2) Determine the temporal expression pattern of MyoD, IGF1 and Fol genes which are related to development, differentiation, and growth of the skeletal muscles during pre-hatching stages and at 1 day old chick.
To achieve these objectives we used the following methodology
Samples were collected from Sakha poultry production research station, Animal production institute, ministry of agriculture, Kafr El-Sheikh, Egypt
For histological examination, 12 samples were collected from embryos of stage HH12 (D2), HH20 (D3), HH24 (D4), HH27 (D5) (3 embryos for each stage).
For scanning electron microscopic examination 8 samples were collected from embryos of stage HH12 (D2), HH20 (D3), HH24 (D4), HH27 (D5) (2 embryos for each stage).
For molecular examination, 50 samples were collected from pieces of thigh muscles from HH24 (D4), HH31 (D7), HH39 (D13), HH43 (D17), and HH46 (newly hatched chicks) (10 embryos for each stage).
RNA was extracted from the tissue samples and was reverse transcribed to cDNA which was used as a template for identification of MyoD, IGF1 and Fol gene expression using polymerase chain reaction (PCR) and image J software.
Results were summarized as the following:-
Skeletal muscles originated from the dermomyotome that has DML and VLL.
At stage HH12-20, the myotome was originated from the DML of the dermomyotome, but doesn’t fill the myocoele. During stage HH 24, the myotome filled the myocoele completely and consisted of epaxial and hypaxial part. By HH 27, the myotomal cells migrated dorsally from epaxial myotome as progenitor cells for the skeletal muscles of the back and ventrally from hypaxial myotome to form skeletal muscles of limbs and body wall.
MyoD expression in the muscles of chick embryo was high on D7, and then this expression level suffered a significant decline till the latest examined stage, 1day old chick.
IGF1 gene expression in muscles of chick embryo started low on the 4th day of incubation, increases gradually till reach the peak on D7 and D13 then gradually down-regulates on D17 and 1 day old chick.
Follistatin gene expression in muscles of chick embryo started low on the 4th of incubation and increased gradually till reaching its peak on D13. This expression was suddenly down-regulated on D17. There is a close similarity between IGF1 and Follistatin gene expression pattern.