Nitric oxide (NO) content and expression of genes involved in myogenesis in embryonal tissues of chickens (Gallus gallus domesticus L.)

Nitric oxide is known to be involved in myogenesis in birds. Previously, we established that in the embryos of poultry bred for meat, intensive oxidation of nitric oxide occurs while in the embryos of egg hens it is insignificant and NO accumulates in donor compounds. Within the breed, line and cross, the degree of oxidation of embryonic NO varied by no more than 15 %, and this trait is inherited. In this regard, a number of questions arise. If meat productivity is somehow related to the degree of oxidation of nitric oxide, then what is its role? Does NO itself or its oxidation products have an epigenetic effect during embryogenesis? How is NO oxidized in embryonic tissues and what is the direct physiological role of this process? Is it possible to regulate embryo development by influencing NO synthesis or stimulating its oxidation? The purpose of the work was to compare changes in the NO content in the tissues of meat and egg chicken embryos with changes in the expression of a number of genes involved in myogenesis, in order to elucidate the mechanisms of the possible epigenetic effect of NO as a factor in the regulation of embryonic development. We have shown that the expression of several genes responsible for myogenesis is associated with the concentration of NO in donor compounds. For the study, embryos of chickens ( Gallus gallus domesticus L.) of the Hisex White egg cross and the mini-meat breed (line A77, group 2), characterized by high and low intensity of embryonic NO oxidation, respectively, were used. In tissues of the embryo homogenate on day 6 and in homogenates of pectoral and thigh muscles on day 14, the expression of seven genes involved in or influencing myogenesis was assessed. These are the genes for myocyte proliferation factor 2c (Mef 2c), myogenic differentiation 1 (MyoD1), myogenesis factor 5 (Myf 5), myosin (Myh 1), myogenin (Myog), myostatin (MSTN), and growth hormone receptor (GHR). The housekeeping gene TBP (TATA-binding protein gene) was a reference gene. During incubation, we assessed the concentration of embryonic NO, the intensity of its oxidation and the transcriptional activity of myogenesis genes as influenced by in ovo administered nitroarginine (NA), a blocker of NO synthesis, and green light that intensifies the oxidation of embryonic NO to nitrate but does not affects the intensity of NO synthesis. NA, when administered before incubation, on day 6, led to a 70 % decrease in the concentration of NO donor compounds in the embryo homogenate and increased the expression of the MyoD1 , Myog and Mef 2c genes in the embryos of Hisex White egg cross. In the mini-meat chickens (line A77, group 2), which are characterized by a low level of deposited NO, the same trend occurred, that is, a decrease in the concentration of donor compounds and an increase in the expression of the MyoD1 , Myog and Mef 2c genes, but the difference between the control and test embryos was less pronounced. The use of green light during incubation also contributed to an increase in the expression of the MyoD1 , Myog and Mef 2c genes on day 6. Based on these data, it can be assumed that the expression of these genes is affected by the concentration of accumulated NO in the embryo tissues. Factors that cause a decrease in the concentration of accumulated NO increase gene expression, regardless of the method of NO reduction (due to less synthesis or more active oxidation). Therefore, the oxidation of NO in the tissues of the embryo may be a way of regulating gene expression. Mechanisms that ensure this oxidation, are inherited. Artificial regulation of the level of NO donors in embryonic tissues is problematic, since arginine, the source of NO in the avian embryo, is in a saturation concentration for NO synthase, and the NO synthesis blocker nitroarginine effectively suppresses NO synthesis only during the first 7 days of incubation. Nevertheless, the rate of NO oxidation in the embryo is a highly sensitive parameter for selection.