after that detour, back to the selection pressure for fat deposition question
Biosci Biotechnol Biochem. 2000 Oct;64(10):2240-2.
http://www.ncbi.nlm.nih.gov/pubmed/11129604
Differential response of obese gene expression from fasting in bovine adipose tissues.
Kim H1, Chi Y, Chung K, Kim K, Choi Y, Baik M.
Abstract
To understand the molecular mechanism for intramuscular fat deposition, the expression of the obese gene was examined in response to fasting. Food deprivation for 48 h induced a decrease in the level of obese mRNA in pooled adipose tissues (abdominal, perirenal, subcutaneous, intermuscular and intramuscular). The expression of obese mRNA was examined for individual adipose tissue from several fat depots. It was highly expressed in perirenal adipose tissue, but fasting did not affect its expression level in this tissue. Moderate levels were detected in subcutaneous and intermuscular adipose tissues, and a fasting-induced decrease in obese mRNA was apparent in these tissues. The expression level of the obese gene in intramuscular adipose tissue was very low and did not respond to fasting.
So, yes, it seems to be about those little cells filling up or emptying out depending upon the energy requirements. But, rather than thinking about this in terms of gluttony and a fast track to marbling, I am trying to think of it in terms of reproductive fitness. I think it was Mill Iron who said that cows are supposed to fluctuate in weight between winter and summer, and his made up for their weight loss over the winter by getting fat in the summer. Seems natural enough. I read in one of those old accounts of cattle in Scotland, that the best meat was the "new meat" laid on in the summer after the animal had starved over the winter. The experts always tell us once you lose that fat, the meat will never marble, but I wonder.
But about fertility and milk production vs. fat deposition. I was thinking about my Galloway cattle, who seem to have not much milk, but what they have seems to be "thick" and "high test". The Galloways also store fat in the muscle instead of between the muscles or as back fat. Maybe they can get it out faster that way. These cattle are evolved to survive hard times in a cold wet climate with scant forage. They fatten easily.
Studying that, I came up with this about the Obese Gene and Milk Fat
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0063406
excerpts for those who don't like to plow through all that jargon:
Although a number of cellular, molecular and genetic studies have been performed with FTO, its functions and effects are far from being understood. Even less is known about RPGRIP1L. Considering that the FTO gene including its linked genomic neighborhood affects fat deposition in humans, the question arises, whether this gene region also affects the amount of fat delivered in milk during lactation. If the FTO locus does not only affect fat synthesis but is also involved in the regulation of energy balance, we would also expect additional effects on other milk components.
Our findings suggest that the FTO region not only regulates milk fat yield, but also the total energy content of milk. With regard to GWAS in humans, the FTO region has been repeatedly associated with body mass index and obesity. However, studies with lean mass have not been performed. To further test the pleiotropic effects of the FTO region, the analysis of traits characterizing body composition would be of interest. But body mass measurement of dairy cattle is not a matter of routine under production conditions.
The effects of the genetic variation in the FTO region accounted for about 1% of the corresponding traits variance in the analyzed cattle population. Even if the effect is small, it seems to be consistent across species and deserves more attention as a factor contributing to complex traits, which are expected to be formed by small effects of many loci [7].
In summary, our study in dairy cattle provides evidence that the obesity-associated FTO gene region accounts for variation in milk fat yield. For the first time, we show that the region does not only control fat but also protein yield and that both milk composition traits are regulated in the same direction. Therefore, we suggest that the FTO gene region controls the energy amount secreted during lactation. The position of the associated haplotype blocks and SNPs, their direction of effect and allele frequency distribution detected in our cattle study suggest that at least two causative variants account for differences between genotype classes. These mutations most likely underlie different selection pressure for production traits. In turn, this indicates different biological functions of the involved gene variants with respect to control and regulation of fat and protein metabolic pathways and in regard to maintaining energy homeostasis and controlling energy partitioning. Besides FTO, the neighboring upstream gene RPGRIP1L and the downstream non-coding genes U6ATAC and 5 S rRNA have functional relevance for milk fat and protein yield.
