Effect of variation in ovine WFIKKN2 on growth traits appears to be gender-dependent

RNA-Seq data provide new insights into the molecular regulation of breast muscle glycogen reserves, a key factor in muscle function and meat quality in chickens

Research is needed to better understand the molecular mechanisms that influence muscle glycogen reserves in chickens due to their critical influence on muscle function and meat quality. In this study, breast muscle RNA sequencing data (RNA-Seq) were used to compare the transcriptomic profile of two original chicken lines divergently selected for breast muscle ultimate pH, which is a proxy for glycogen reserves. Weighted gene co-expression network analysis (WGCNA) of muscle and jejunum RNA-Seq data was also performed to highlight biological processes specifically involved in the gut-muscle dialogue that may contribute to the divergence in glycogen reserves between the two lines. Breast muscle RNA-Seq analysis of 4-week-old birds from the 15th generation of selection, in which glycogen reserves in the pHu- line were twice as high as that in the pHu+ line, revealed 2676 differentially expressed genes (Padj ≤ 0.05). Functional analysis of the genes overexpressed in the pHu- line highlighted enrichment in processes related to energy production from a wide range of substrates and pathways, as well as to processes involved in development of blood and lymph tissue. Diverse processes were enriched for genes overexpressed in the pHu+ line: muscle development and remodeling, lipid metabolism, immune response and inflammation, which suggested molecular changes much larger than those for carbohydrate metabolism. WGCNA revealed 64 modules of co-expressed genes. One, which contained 30 % genes expressed in the jejunum and 70 % genes expressed in the muscle, was correlated (P ≤ 0.05) with muscle glycogen reserves and several indicators of intestinal anatomy and health. Functional analysis of it showed an enrichment of processes related to transmission of nerve information and tissue oxygenation that seem to be involved in the gut-muscle dialogue that mediates establishment of breast muscle glycogen reserves. Finally, the study found that transcriptional regulations observed in muscle of the pHu+ line were similar to those in muscle afflicted with "wooden breast", which highlighted a dysfunction of mitochondrial metabolism and suggested several potential gene markers for both conditions.

RNA-sequencing revisited data shed new light on wooden breast myopathy

Wooden Breast (WB) abnormality represents one of the major challenges that the poultry industry has faced in the last 10 years. Despite the enormous progress in understanding the mechanisms underlying WB, the precise initial causes remain to be clarified. In this scenario, the present research is intended to characterize the gene expression profiles of broiler Pectoralis major muscles affected by WB, comparing them to the unaffected counterpart, to provide new insights into the biological mechanisms underlying this defect and potentially identifying novel genes likely involved in its occurrence. To this purpose, data obtained in a previous study through the RNA-sequencing technology have been used to identify differentially expressed genes (DEGs) between 6 affected and 5 unaffected broilers' breast muscles, by using the newest reference genome assembly for Gallus gallus (GRCg7b). Also, to deeply investigate molecular and biological pathways involved in the WB progression, pathways analyses have been performed. The results achieved through the differential gene expression analysis mainly evidenced the downregulation of glycogen metabolic processes, gluconeogenesis, and tricarboxylic acid cycle in WB muscles, thus corroborating the evidence of a dysregulated energy metabolism characterizing breasts affected by this abnormality. Also, genes related to hypertrophic muscle growth have been identified as differentially expressed (e.g., WFIKKN1). Together with that, a downregulation of genes involved in mitochondrial biogenesis and functionality has been detected. Among them, PPARGC1A and PPARGC1B chicken genes are particularly noteworthy. These genes not only have essential roles in regulating mitochondrial biogenesis but also play pivotal roles in maintaining glucose and energy homeostasis. In view of that, their downregulation in WB-affected muscle may be considered as potentially related to both the mitochondrial dysfunction and altered glucose metabolism in WB muscles, and their key involvement in the molecular alterations characterizing this muscular abnormality might be hypothesized.

WFIKKN1 and WFIKKN2: "Companion" proteins regulating TGFB activity

The WFIKKN (WAP, Follistatin/kazal, Immunoglobulin, Kunitz and Netrin domain-containing) protein family is composed of two multidomain proteins: WFIKKN1 and WFIKKN2. They were formed by domain shuffling and are likely present in deuterostoms. The WFIKKN (also called GASP) proteins are well known for their function in muscle and skeletal tissues, namely, inhibition of certain members of the transforming growth factor beta (TGFB) superfamily such as myostatin (MSTN) and growth and differentiation factor 11 (GDF11). However, the role of the WFIKKN proteins in other tissues is still poorly understood in spite of evidence suggesting possible action in the inner ear, brain and reproduction. Further, several recent studies based on next generation technologies revealed differential expression of WFIKKN1 and WFIKKN2 in various tissues suggesting that their function is not limited to MSTN and GDF11 inhibition in musculoskeletal tissue. In this review, we summarize current knowledge about the WFIKKN proteins and propose that they are "companion" proteins for various growth factors by providing localized and sustained presentation of TGFB proteins to their respective receptors, thus regulating the balance between the activation of Smad and non-Smad pathways by TGFB.