Research areas

The study of factors that influence the development of adipose tissue in farm animals.

White adipose tissue, whose main function is to act as an energy reserve, enables animals to survive, ensuring the supply of energy when food is scarce. This is achieved thanks to the ability of this tissue to 'expand' when it is necessary to store food reserves and 'contract' when the reserves are needed. Both processes occur under narrow modulation of the mechanisms of fat synthesis and hydrolysis. In the field of animal production an excessive accumulation of fat in adipose deposits results in an increase in the conversion indices and the financial depreciation of these fatty carcasses as the consumer demands products that are low in fat. Furthermore, and due also to the new consumer preferences, the market is demanding products with an appropriate proportion of the so called healthy fatty acids of the omega-3 type. It is therefore of great interest to understand the mechanisms involved in fatty tissue development and in adipogenesis and to achieve the identification of factors that can modulate the quantity of the composition of the adipose deposits.

Our work, above all, concerns the study of ruminants (bovine and ovine), although we have also studied the fat tissue in animals of the porcine species. The great majority of the results of research and knowledge referred to in the literature on the initiation and maintenance of the differentiation process has been obtained using cell lines or primary cultures of human adipose tissue. However, there have been very few studies of farm animals. There are some studies of pigs but there are very few studies of ruminant animals. Furthermore, ruminants have certain characteristics that differentiate them from others in terms of the metabolism of adipose tissue.

It is well known that adipocyte differentiation is regulated by a sequential expression of transcriptional activators, amongst which are CCAAT/enhancer binding protein (C/EBP) and the family of peroxisome proliferator-activated receptors (PPAR). These transcription factors coordinate the expression of the genes involved in the creation and maintenance of the phenotype of the adipocytes: for example the genes for the fatty acids binding protein, the glucose transporter 4, the lipoprotein lipase, phosphoenolpyruvate carboxilase and the leptin.

The mechanisms suggested by different authors, in studies using cell lines and human adipocytes to stimulate adipogenesis through the C/EBPd and PPAR receptors are: an increase in the PPAR ligand production; stimulation of the PPARg expression; stimulation of the PPARg expression and activation of specific gene expression. Similarly, the proposed mechanisms to inhibit adipogenesis are: the repression of the promoters; interference in the activation of the C/EBPd and PPAR genes and blocking the positive feedback loop between C/EBPd and PPARg.

It has been demonstrated that there are different compounds that may influence the preadipocytes differentiation process. Having demonstrated that the effects of retinoic acid are mediated by RAR receptors, for example, retinoic acid (RA) prevents the induction of the adipogenic factors PPARg and C/EBPa, it has been suggested that the inhibiting effect of adipogenesis, produced by retinoic acid, is mediated by a blocking of the transcriptional activity of the C/EBP proteins caused by the RAR receptor bonded to its ligand. Similarly the induction of PPARg expression is averted, and can also be subsequently reverted, through the presence of retinoic acid.

In our laboratory we are currently studying the effect of retinoic acid and linoic acid combined with the differentiation of ovine preadipocytes from two different anatomical deposits: omental and subcutaneous. To do this we are using primary cultures and after inducing differentiation, we analysed the level of expression of the principal transcription factors and the differentiation of adipocyte marker genes. Using primary preadipocytes ovine cultures as a model we want to clarify which factors, out of those involved in the transcriptional cascade, are responsible for the initiation of adipogenesis and its subsequent maintenance; the extent to which they are responsible, and the effect caused by the above-mentioned compounds

The study of molecular markers in genes of interest for animal production

The appearance of transmissible sponge form encephalopathy in ovine livestock and the incidence scrapie has lead to genotyping of flocks of sheep in different European countries. This disease is characterised by the accumulation of an anomalous form of cellular prion protein or PrPC, called PrPSc. It has been shown that the incidence of scrapie in sheep is associated with polymorphism in the PrP gene: codon 136 which codifies for alanine (A) or valine (V); codon 154 which codifies for arginine ® or histadine (H) and codon 171, which codifies for glutamine (Q) histadine (H) or arginine (R). It is also known that homozygous animals for the allele ARR are resistant to the disease whereas those carriers of the allele VRQ have a greater risk of contracting it. The relationship between genotypes for the PrP gene and the incidence of scrapie enables this information to be used in systems of ovine livestock selection in such a way that it is possible to control this disease, eliminating animals which are carriers of the sensitive allele (VRQ) and selecting the carriers of the resistant allele (ARR); establishing in this way a classification system in which the different genotypes are assigned to different risk groups as a function of their susceptibility / resistance to contracting scrapie. However, the introduction of this new objective in livestock improvement programmes could have repercussions for the genetic progress and other productive characteristics of the animals such as milk and meat production.

Our team has been participating in a project whose objective was the characterisation of the PrP gene in ovine breeds in Spain and the study of the application of the results obtained to the animal selection systems. Specifically two milk producing breeds, Assaf and Lacaune, from Navarra have been genotyped and the existence of an association between the various polymorphisms described in the PrP gene and their milk producing characteristics have been analysed.

Application of molecular techniques to ensure the traceability and authenticity of products of animal origin

In recent years we have witnessed a significant increase in the sale of meat under quality certified brands, guarantees of geographical origin etc. It is essentially a question of offering a product, which, amongst other characteristics, offers an unequivocal guarantee of its origin. In this context traceability is one of the foundations of this certification. It is therefore important to have highly reliable auditing tools for these tracing systems. One of these tools, without doubt highly reliable for animal identification, is based on comparison of genetic information, in this case between the cuts of meat offered for sale and the animals from which they come.

In our laboratory we have perfected a technique, based on the analysis of genetic information provided by a combination of between 8 and 11 DNA microsatellite markers (STR) that can confirm the origin of the meat with a level of certainty of virtually 100%.

Taking samples must be carried out both from the live or recently slaughtered animal, the reference samples, and from the cuts of meat, the verification samples. Once these reach the laboratory an analysis is carried out on both samples. Firstly DNA is extracted and this is subjected to a polymerase chain reaction (PCR) in such a way that the chosen microsatellites are amplified. Subsequently, the size of the amplified microsatellites is determined using an automatic DNA sequencer. In this way the profiles obtained can be interpreted with DNA fragment analysis software and the genotype of each sample can be defined. That is to say: which pair of alleles presents for each one of the analysed markers. Obviously identical samples come from the same animal.

This system of genetic traceability has been used as a tool to monitor the brand "Veal from Navarra" since the year 2000. Each year 1% of the slaughtered animals carrying this brand mark is analysed. It is also used for other quality meat brands.