Sheep Mammary Tissue Research Articles

Feeding level regulates the expression of some genes involved with programed cell death and remodeling in goat and sheep mammary tissue.

Mammary tissue (MT) turnover is characterized by programed cell death and remodeling which might be affected by both feeding level and animal species. Thus, twenty-four dairy goats and the same number of sheep were assigned to three homogenous sub-groups per animal species and fed the same diet in quantities which met 70% (FL70), 100% (FL100) and 130% (FL130) of their daily energy and crude protein requirements. Individual MT samples were taken by biopsy from the animals on the 30th and 60th experimental day. The results showed, in the first sampling time, a significant reduction in the mRNA abundance for selected genes involved in programed cell death in both FL 70 fed goats (STAT3 and BECN1) and sheep (CASPASE8 and BECN1) compared with the respective FL100 groups. The FL130, in comparison with the FL100, caused a significant increase in transcripts accumulation of STAT3 gene in both sampling times and CASPASE8 gene in the second sampling time in goat MT, while the opposite happened for the mRNA expression of CASPASE8 and BECN1 genes in sheep MT, but only in the first sampling time. Moreover, a significant up regulation in the mRNA levels of MMP2 gene in MT of FL130 fed sheep was observed. The FL130, in comparison with the FL70, caused an enhancement in the mRNA expression levels of BECN1, CASPASE8, BAX and STAT3 genes in goat MT only. It was also shown that apoptosis and autophagy can be affected simultaneously by the feeding level. Overfeeding affects MT programed cell death and remodeling by a completely different way in goats than sheep. In conclusion, feeding level and animal species have strong effects on both MT programed cell death (apoptosis and autophagy) and remodeling but the molecular mechanisms need further investigation.

The effect of long term under- and over-feeding on the expression of six major milk protein genes in the mammary tissue of sheep.

Milk protein synthesis in the mammary gland involves expression of six major milk protein genes whose nutritional regulation remains poorly defined. In this study, the effect of long term under- and over-feeding on the expression of αs1-casein: CSN1S1, αs2-casein: CSN1S2, β-casein: CSN2, κ-casein: CSN3, α-lactalbumin: LALBA and β-lactoglobulin: BLG gene in sheep mammary tissue (MT) was examined. Twenty-four lactating dairy sheep, at 90-98 d in milk, were divided into three groups and fed the same ration, for 60 d, in quantities which met 70% (underfeeding), 100% (control) and 130% (overfeeding) of their energy and crude protein requirements. The results showed a significant reduction on mRNA of CSN1S1, CSN1S2, CSN2 and BLG gene in the MT of underfed sheep compared with the overfed ones and a significant reduction in CSN3 and LALBA gene expression compared with the respective control animals. Significant positive correlations were observed between the mRNA levels of milk proteins' genes with the milk protein yield and milk yield respectively. In conclusion, the feeding level and consequently the nutrients availability, affected the milk protein yield and milk volume by altering the CSN1S1, CSN1S2, CSN2, CSN3, LALBA and BLG gene expression involved in their metabolic pathways.

The effect of long term under- and over-feeding on the expression of genes related to glucose metabolism in mammary tissue of sheep.

Glucose utilisation for lactose synthesis in the mammary gland involves expression of a large number of genes whose nutritional regulation remains poorly defined. In this study, the effect of long term under- and over-feeding on the expression of genes [glucose transporter 1: GLUT1, glucose transporter 3: GLUT3, Sodium glucose contransporter 1: SGLT1, two isoforms of β- (1,4) galactosyltransferase: β- (1,4) GAT1, β- (1,4) GAT3 and α-lactalbumin: LALBA] related to glucose metabolism in sheep mammary tissue (MT) was examined. Twenty-four lactating dairy sheep were divided into three homogenous sub-groups and fed the same ration in quantities which met 70% (underfeeding), 100% (control) and 130% (overfeeding) of their energy and crude protein requirements. The results showed a significant reduction on mRNA of GLUT1 and LALBA gene in the MT of underfed sheep, compared with the respective controls and overfed and a significant reduction on mRNA level of SGLT1 and β- (1,4) GAT1 in the MT of underfed sheep, compared with the overfed ones. A significant increase in the GLUT3 mRNA accumulation in the MT of both under- and over- fed sheep was found. Additionally, a trend of reduction on β- (1,4) GAT3 mRNA level in the MT of the underfed sheep, compared with the overfed, was observed. A close positive relationship was obtained between the mRNA transcripts accumulation of GLUT1, SGLT1, β- (1,4) GAT1 and LALBA gene with the milk lactose content and milk lactose yield respectively. In conclusion, feeding level and consequently nutrient availability, may affect glucose uptake and utilisation in sheep MT by altering the GLUT1, GLUT3, SGLT1, β- (1,4) GAT1 and LALBA gene expression involved in their metabolic pathways.

The effect of long term under- and over-feeding on the expression of genes related to lipid metabolism in mammary tissue of sheep.

Milk fatty acid (FA) synthesis by the mammary gland involves expression of a large number of genes whose nutritional regulation remains poorly defined. In this study, we examined the effect of long-term under- and over-feeding on the expression of genes (acetyl Co A carboxylase, ACC; fatty acid synthetase, FAS; lipoprotein lipase, LPL; stearoyl Co A desaturase, SCD; peroxisome proliferator activated receptor γ2, PPARγ2; sterol regulatory element binding protein-1, SREBP-1c; and hormone sensitive lipase, HSL) related to FA metabolism in sheep mammary tissue (MT). Twenty-four lactating sheep were divided into three homogenous sub-groups and fed the same ration in quantities covering 70% (underfeeding), 100% (control) and 130% (overfeeding) of their energy and crude protein requirements. The results showed a significant reduction of mRNA of ACC, FAS, LPL and SCD in the MT of underfed sheep, and a significant increase on the mRNA of LPL and SREBP-1c in the MT of overfed compared with the control respectively. In conclusion, the negative, compared to positive, energy balance in sheep down-regulates ACC, FAS, LPL, SCD, SREBP-1c and PPARγ2 expression in their MT which indicates that the decrease in nutrient availability may lead to lower rates of lipid synthesis.

Prolactin Signaling in Mammary Gland Development

Prolactin Signaling in Mammary Gland Development

Identification of mammary-derived growth inhibitor in sheep mammary tissue

This study was conducted to evaluate the presence of mammary-derived growth inhibitor (MDGI) in mammary tissue obtained from 11 lactating or pregnant Dorset ewes. MDGI is a protein involved in regulation of mammary epithelial proliferation and differentiation. Results revealed the presence of a 13 kDa MDGI protein in all samples analyzed. The majority (90%) of MDGI was found in the cytoplasmic fraction and the remaining (10%) in the microsomal fraction of sheep mammary tissue. Results indicated that MDGI protein concentrations in mammary tissue obtained from 110 or 140 days in pregnancy were equal or higher than in mammary tissue obtained from lactating animals. High levels of MDGI in sheep mammary tissue at times of intense growth and proliferation are consistent with a role of MDGI as a differentiation rather than anti-proliferative factor. Treatments that increase MDGI production would favor mammary epithelial cell differentiation and could increase milk production. This is a first report on sheep MDGI.

Gene Transfer into Mammalian Cells by Jet Injection

Jet injection of DNA in solution is a technique that can be used to transfer DNA into tissues of living animals, where the introduced genes are expressed. The muscle, fat, skin, and mammary tissue of mice, and the fat, skin, and mammary tissue of sheep can be transfected with DNA. A jet injector, such as the Ped-o-jet (Stirn Industries, Dayton, NJ), is used to form a jet from 100 to 300 microliters of a DNA solution. This jet has sufficient force to travel into and through tissues of adult and juvenile animals. The introduced DNA is found in cells surrounding the path of the jet. When jet injection is performed through the surface of intact skin, underlying muscle, mammary, and fat, cells up to 2 cm distant from the point of injection are transfected with DNA. In this study, we demonstrate that the efficiency of DNA transfer is dependent upon the force of injection. Jet injection is an alternative to needle injection, lipofection, and particle bombardment for the introduction of "naked" DNA into the tissues of animals. This technique has potential for the introduction of genes into living organisms for genetic vaccination and gene therapy.

Metabolic Adaptations in Fatty Acid and Lactose Biosynthesis by Sheep Mammary Tissue During Cessation of Lactation

The effect of involution of fatty acid synthesis, lactose synthesis, and carbon dioxide production by sheep mammary tissue was examined. Mammary tissue from lactating or nonlactating (9 days after weaning) sheep was used for measurements of biosynthetic capacities (in vitro incubations) and enzymatic activities. Termination of lactation decreased biosynthetic rates of fatty acid and lactose synthesis 99 and 97%. Similarly, rates of acetate and glucose oxidation to carbon dioxide by mammary tissue from nonlactating sheep relative to lactating sheep decreased 84 and 98%. Of enzymes in fatty acid synthesis, acetyl-CoA carboxylase decreased the most dramatically as a result of involution (99%). Other major decrease were for acetyl-CoA sythetase (79%) and fatty acid synthetase (85%) while enzymes involved in reducing equivalent generation (glucose-76-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, and NADP-isocitrate dehydrogenase) decreased less dramatically. for enzymes in lactose synthesis, involution decreased UDP-glucose 4-epimerase (76%), UDP-glucose pyrophosphorylase (87%), and lactose synthetase (93%) while activity of phosphoglucomutase remained unchanged. With the termination of lactation, the magnitude of alterations in rates of fatty acid sythesis and lactose synthesis compared most closely to decreases in acetyl-CoA carboxylase activity and lactose synthetase activity, respectively.

Fatty Acid Synthesis in Sheep Mammary Tissue

Biochemical pathways of fatty acid synthesis in sheep mammary tissue were investigated. Ewes were sacrificed (3 to 4 wk postpartum) for mammary tissue for tissue slice incubations and enzyme assays. Acetate was readily incorporated into fatty acids by sheep mammary slices. However, lipogenesis from glucose, glycerol, and pyruvate was limited, indicating inability to utilize acetyl coenzyme A generated in the mitochondria for fatty acid synthesis. Coinciding with lack of mitochondrial acetyl coenzyme A utilization for fatty acid synthesis was an absence of two citrate-cleavage pathway enzymes (ATP-citrate lyase and NADP-malate dehydrogenase). Sources of reducing equivalents necessary to support lipogenesis were also examined. Comparison of acetate incorporation into fatty acids in the presence and absence of glucose indicated that approximately one-half of the reducing equivalents can originate from pathways not involving the pentose phosphate cycle. Results were consistent with these reducing equivalents being produced via NADP-isocitrate dehydrogenase. In sheep mammary tissue, activity of NADP-isocitrate dehydrogenase was 6 to 12-fold greater than glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase activities. Presumably because of the premium on glucose and the availability of acetate, sheep mammary tissue has adapted to spare glucose in two ways: first, to utilize acetate but not glucose as a carbon source for fatty acid synthesis and second, to generate a portion of the reducing equivalents from acetate via the isocitrate pathway.

Intracellular concentrations of sodium, potassium and chloride in the lactating mammary gland and their relation to the secretory mechanism.

1. The intracellular (I.C.) concentrations of Na, K and Cl in mammary cells from lactating guinea-pigs have been calculated from the analysis of fresh tissue and the measurement of the extracellular (E.C.) space with [(14)C]sucrose and the milk content with [(14)C]lactose.2. Assuming that alveolar milk has the same concentration as teat milk, the intracellular concentrations were calculated to be K 115, Na 42 and Cl 66 m-equiv. l(-1) intracellular water.3. Intracellular concentrations were also calculated in slices incubated in Krebs-bicarbonate medium plus glucose. There was a large increase in the sucrose (E.C.) space and a rise in total tissue [Na] and [Cl]. On the assumption that the medium had equilibrated with the milk space as well as the E.C. space, the calculated I.C. concentrations of Na (43 m-equiv. l(-1)), and Cl (62) were very similar while [K] was somewhat higher (143 m-equiv. l(-1)I.C. water).4. The calculated I.C. concentrations of all three ions are all higher than in milk but the ratios between them are almost identical.5. Similar figures for the I.C. concentrations of Na, K and Cl have been obtained in the goat, cow and sheep mammary tissue incubated in vitro.6. Moderate changes in the concentrations of Na, K and Cl in the external medium had no effect on cell composition but during incubation without ions [(14)C]sucrose became distributed throughout the total tissue water indicating that sucrose had entered the I.C. compartment.7. Acetazolamide (10(-2)M), aldosterone (1.4 x 10(-6)M) and, in some experiments, lack of glucose lowered I.C. [Cl(-)], but oxytocin, vasopressin and low doses of insulin had no effect.8. The data are difficult to reconcile with the hypothesis of Zaks, Natochin, Sokolova, Tanasiichuk & Tverskoi (1965) that freshly secreted milk has the ionic composition of plasma.9. Comparison of I.C. ion concentrations and the membrane potential between the cells and milk suggests that Na(+) and K(+) are passively distributed across the apical membrane but that Cl(-) must be actively held in the cells. Across the basal membrane the data are consistent with the presence of a Na(+) pump and with Kinura's (1969) detection of a Na:K ATPase on the basal and lateral membranes. In addition another inward-facing Cl(-) pump may exist at this site.