Abstract: 【Objective】Insulin-like growth factor I (IGF-I)-calcineurin (CaN)-NFAT signal pathway have been implicated in the regulation of myocyte hypertrophy and fiber type specificity. In the present study, expression of CnAα, NFATc3 and IGF-I genes was firstly studied in Gaoyou and Jinding ducks differing in their muscle growth rates. 【Method】 Expression of IGF-I, CnAα and NFATc3 was quantified by RT-PCR in the breast muscle (BM) and leg muscle (LM) on days 13, 17, 21, 25 and, 27 of embryonic development, as well as at 7 days post-hatching (PH). Lateral gastrocnemius muscles collected from two duck breeds were cut at -20℃ using a cryotome and then stained with the method of myosin-ATPase in order to analyze muscle fiber type composition. SPSS 20.0 software was used to conduct the significant difference analysis, for investigating the possible regulation mechanism of IGF-I-CaN-NFAT pathway in myofiber type transition. 【Result】 Overall, the percentage of type I fibers increased and that of type IIb fibers decreased consistently. However, the percentage of type IIa fibers was almost constant as development proceeded in both duck breeds. The consistent expression patterns of CnAα, NFATc3 and IGF-I were found in the same anatomical location at different development stages in both duck breeds, showing extremely significant differences in age-specific fashion. However, the three genes were differentially expressed in different anatomical location (BM and LM). CnAα, NFATc3 and IGF-I mRNA could be detected as early as on E 13d, and the highest level was appeared at this stage in both BM and LM, significantly higher than those at the other five development stages, indicating that these three genes might have some effects on the ontogenesis of myofibers. The mRNA expression of duck CnAα in BM showed a tendency as the “V”, the lowest level appeared on E 21d, and then increased continuously up until 7 days PH in both duck breeds, while in LM, CnAα gene expression was variable throughout the course of this study and the lowest level appeared on E 27d. Expression of NFATc3 decreased significantly to a very low level from E 13d to E 17d and maintained this relative low level during late development stages in both BM and LM, the lowest level appeared on E 21d in BM while the expression level on E 21d in LM was significantly higher (P＜0.05) than those on embryonic days 17, 25 and 27, and at 7 days PH. Expression of IGF-I declined to the lowest level just prior to hatch (E 27d), and then elevated a little on 1 week PH in both BM and LM in the two duck breeds. Significant positive relationships were observed for the expression of studied genes in BM and LM of both duck breeds. Meanwhile, the expression of these three genes were all showed positive relationships with the percentage of type IIb fibers and negative relationships with the percentage of type I fibers and type IIa fibers. 【Conclusion】The data of the study indicate that the fiber type of the lateral gastrocnemius muscle may transit from type IIb to type I during late-embryonic and PH development, and differential expression and coordinated developmental regulation of the selected genes that comprise the IGF-I-calcineurin-NFATc3 pathwayin the duck skeletal muscles during embryonic and early PH growth and development, and this signaling pathway might play a role in the regulation of the myofiber type transition.

Key words: early development, gene expression, myofiber type; IGF-I-calcineurin-NFATc3 pathway, duck