Abundance of MyoD and myostatin transcripts in chicken embryos submitted to distinct incubation temperatures and timing exposures.

563 The formation of skeletal muscle tissue is directly modulated by intricate expressing the distinct signalling molecules orchestrated by the myogenic regulatory factors, such as the myogenic determination factor MyoD, that activates the transcription of muscle-specific genes by binding to consensus DNA sites found in the regulatory sequences of these genes, differentiate and fuse the myoblasts in order to form the muscle fibres (Buckingham, 2006). Its expression is detected at an earlier stage of myogenesis when quiescent stem cells rapidly expand in number to generate the myoblasts needed to repair tissue damage (Glass, 2010) and several studies have demonstrated that MyoD is sufficient and necessary for the formation or survival of skeletal myoblasts (Emerson, 1993; Buckingham, 2006). In this context, it was already well characterised that myostatin is a secreted growth and differentiation factor belonging to the transforming growth factor (TGF)-beta superfamily that exert an important modulator role of body composition in experimental animals by controlling the proliferation of myoblasts, followed by inhibiting the differentiation of these cells (Rodgers and Garikipati, 2008; Glass, 2010). Few reports in the literature have investigated how the abundance of myogenic regulatory genes is altered in chicken embryos exposed to distinct adverse incubation temperatures and timing exposures (Gabriel et al., 2003, 2006). Based on this evidence, the purpose of the present study was to quantify the levels of MyoD and myostatin transcripts in chicken embryos exposed to low and high incubation temperatures for distinct timing exposure using real time PCR assays. Fertilised chicken eggs (Gallus gallus domesticus, Linnaeus, 1758) from the Cobb line were maintained in a humidified atmosphere in an incubator (Premium Ecológica, model IP120). After a four-day incubation period at 37 ± 0.5 °C (control incubation condition) and 60% relative humidity, some eggs were transferred to other incubators registering low (33 ± 0.5 °C) and high (44 ± 0.5 °C) incubation temperatures. These eggs remained for one and two hours under these conditions, and at the end of each hour, six embryos per treatment were then collected for further experiments. The collection of embryos on the fourth day of incubation was based on the evidence that Abundance of MyoD and myostatin transcripts in chicken embryos submitted to distinct incubation temperatures and timing exposures