Intramuscular fat content is important for many meat quality parameters. This work is aimed at identifying functional categories of genes associated with natural variation among individuals in intramuscular fat content to help the design of genetic schemes for high marbling potential. Taking advantage of the global nature of transcriptomic and proteomic technologies, 40 genes were identified as differently expressed between high fat and low fat pig Longissimus muscles at slaughter weight. They are involved in metabolic processes, cell communication, binding, and response to stimulus. Using real-time PCR in muscle biopsies taken earlier in the fattening period, the group with a high intramuscular fat content was also characterized by the down-expression of genes playing a negative role in adipogenesis, such as architectural transcription factor high-motility hook A1, mitogen activated protein-kinase14, and cyclin D1. These results suggest that interindividual variability in intramuscular fat content might arise essentially from differences in early adipogenesis.

The content and distribution of body lipids are of special interest for production efficiency and meat quality in the farm animal industry. Triglycerides represent the most variable fraction of tissue lipids, and are mainly stored in adipocytes. Although several studies have reported regional differences in the expression of genes and their products in adipocytes from various species, the characteristics of i.m. adipocytes remain poorly described. To evaluate adipocyte features according to muscle and other fat locations, adipocyte proteins were isolated from trapezius skeletal muscle, and intermuscular, s.c., or perirenal adipose tissues from 6 female pigs (80 d of age). Protein extracts were labeled and analyzed by 2-dimensional, fluorescent, differential gel electrophoresis. The comparisons revealed that 149 spots were always differentially expressed (P < 0.05, ratio exceeding |2|-fold difference) between i.m. adipocytes and the fat cells derived from the 3 other adipose locations. The proteins that were downregulated in i.m. fat cells belonged to various metabolic pathways, such as lipogenesis (cytosolic malate dehydrogenase and isocitrate dehydrogenase, P < 0.01), glycolysis (enolases and aldolase, P

The molecular mechanisms underlying normal and pathological spermatogenesis remain poorly understood. We compared protein concentrations in different germ cell types to identify those proteins specifically or preferentially expressed at each stage of rat spermatogenesis. Crude cytosolic protein extracts and reversed-phase HPLC prefractionated cytosolic extracts from spermatogonia, pachytene spermatocytes, and early spermatids were subjected to two-dimensional difference gel electrophoresis (2-D DIGE). By comparing gels and carrying out statistical analyses, we were able to identify 1274 protein spots with relative abundances differing significantly between the three cell types. We found that 265 of these spots displaying highly differential expression (ratio > or = 2.5 between two cell types), identified by mass fingerprinting, corresponded to 123 nonredundant proteins. The proteins clustered into three clades, corresponding to mitotic, meiotic, and post-meiotic cell types. The differentially expressed proteins identified by 2-D DIGE were confirmed and validated by western blotting and immunohistochemistry, in the few cases in which antibodies were available. 2-D DIGE appears a relevant proteomics approach for studying rat germ cell differentiation, allowing the establishment of the precise expression profiles for a relatively large number of proteins during normal spermatogenesis.

High-quality protein extracts are required for proteomic studies, a field that is poorly developed for marine macroalgae. A reliable phenol extraction protocol using Scytosiphon gracilis Kogame and Ectocarpus siliculosus (Dillwyn) Lyngb. (Phaeophyceae) as algal models resulted in high-quality protein extracts. The performance of the new protocol was tested against four methods available for vascular plants and a seaweed. The protocol, which includes an initial step to remove salts from the algal tissues, allowed the use of highly resolving two-dimensional gel electrophoresis (2-DE) protein analyses, providing the opportunity to unravel potentially novel physiological processes unique to this group of marine organisms.