Ovarian and IGF-I axis control of mammary development in prepubertal heifers

Is bovine somatotropin an alternative strategy to overcome the detrimental effects of high-gain diets on prepubertal Holstein × Gyr heifers?

Feeding high-gain diets and an inadequate energy and protein ratio during pre-puberty may lead to impaired growth and mammary gland development of heifers. Thus, frequent application of bovine somatotropin (bST) may prevent future losses in productivity, improve mammary development and animal performance. We aimed to evaluate the effects of bST on digestibility, performance, blood metabolites, mammary gland development, and carcass composition of high-performance prepubertal Holstein × Gyr heifers. Thirty-four Holstein × Gyr heifers with an average initial body weight of 218 ± 49 kg and 14 ± 4 months of age were submitted to an 84-day trial evaluating the effects of no bST or bST injections. Treatments were randomly assigned to each animal within one of the tree blocks. The bST did not influence digestibility or performance parameters. Regarding blood results, IGF1 concentration presented an interaction between treatment and day, where bST heifers had the highest IGF1 concentration. Heifers receiving bST also showed increased ribeye area; however, only an experimental day effect for backfat thickness was observed, with greater accumulation of carcass fat on day 84. Heifers receiving bST had lower pixels/mm² on parenchyma, characteristic of greater parenchymal tissue. Moreover, heifers on bST treatment also had reduced pixels/mm2, characteristic of reduced fat pad tissue. Lastly, bST injections did not influence liver and muscle gene expression, nor most genes evaluated in mammary gland tissue, except for IGFBP3 expression, which was greater for bST heifers. In summary, we confirm the efficacy of bST injections to overcome the detrimental effects of high-gain diets on mammary gland growth and to improve lean carcass gain of prepubertal Holstein × Gyr heifers.

Effect of red clover isoflavones on hormone, immune, inflammatory, and plasma biochemistry in lactating dairy cows

This study was to conducted to investigate the effect of red clover isoflavones on the health indicated by immune status and blood biochemistry in dairy cows. Sixty-eight healthy Holstein lactating cows were randomly divided into four treatments (n = 17 per treatment) from 5 blocks according to milk yield using a randomized complete block design. No initial differences in parity (2.13 ± 1.21), days in milk (165 ± 21 d), and milk yield (33.93 ± 3.81 kg/d) between groups. Cows were fed the basal diet supplemented with 0, 2, 4, or 8 g/kg red clover extract (RCE) in diet (dry matter based). Feeding, refusal feed weights, and milk yield were recorded three consecutive days in weeks 0, 4, 8, and 12. Blood was collected from the tail vein of the cows on the last day of weeks 4, 8 and 12, 1 h after the morning feeding, and analyzed for hormones, immunoglobulins, inflammatory markers, and markers of liver and kidney activities. The dry matter intake was significantly decreased by 3.7% in the 8 g/kg group (P < 0.05). The fat-corrected milk yield was significantly higher in both of the 2 and 4 g/kg groups (P < 0.01). Plasma estradiol and prolactin showed a quadratic effect with increasing RCE levels, with the highest in the 4 g/kg group (P < 0.05). Plasma tumor necrosis factor (TNF)-α, interleukin (IL)-6, and IL-1β levels decreased linearly with increasing dietary RCE levels. Plasma IL-18 levels showed a quadratic effect with increasing dietary RCE levels, with significantly lower levels in both of the 2 and 4 g/kg groups (P < 0.05). Plasma immunoglobulin A and D-lactic acid levels showed a quadratic effect with increasing dietary RCE levels, with significantly higher level in the 4 g/kg group (P < 0.05). The liver function and kidney activity makers were similar (P > 0.05). These results recommend the supplementation of RCE at a level from 2 to 4 g/kg DM.

Estradiol administration in Holstein heifer calves differentially affects the fatty acid composition of subcutaneous adipose and the mammary fat pad tissues

This research communication reports the relative abundance of fatty acids in mammary fat pad (MFP) and subcutaneous adipose (SCA) tissues for Holstein heifer calves receiving 0, 3, or 12 daily injections of estradiol immediately prior to tissue collection. The objective of this study was to determine if the MFP and SCA fatty acid profiles were affected by estradiol administration and if such a response differs between adipose tissue depots. Twelve Holstein heifer calves were reared on a common diet and administered 12 daily injections prior to euthanasia. Injections were either daily injections of corn oil (n = 4; CON), 9 injections of corn oil followed by 3 injections of estradiol (n = 4; SHORT), or 12 injections of estradiol (n = 4; LONG). Fatty acids were extracted from collected MFP and SCA tissues samples and analyzed using gas chromatography. The MFP tissues contained a greater abundance of saturated fatty acids than SCA tissues which complemented a reduced abundance of mono-unsaturated fatty acids in the MFP than SCA. Extended duration of estradiol administration increased the abundance of total omega 3 fatty acids in both MFP and SCA tissues. There was a treatment by tissue interaction for several of the C18:1 and C18:2 isomers indicating that estradiol's effects on fatty acid uptake and metabolism are tissue specific. Additionally, C18 uptake and metabolisms may have important roles in mammary growth and development. Together, these results indicate that the MFP responds differently to estradiol administration than SCA tissues and that these alterations are associated with different degrees of induced mammary growth via estradiol.

Impacts of postweaning growth rate of replacement beef heifers on their reproductive development and productivity as primiparous cows1

This experiment evaluated the effects of postweaning body weight (BW) gain of replacement beef heifers on their reproductive development and productivity as primiparous cows. Seventy-two Angus × Hereford heifers were ranked on day -6 of experiment (17 d after weaning) by age and BW (218 ± 1.6 d of age and 234 ± 3 kg of BW), and assigned to receive 1 of 3 supplementation programs from days 0 to 182: 1) no supplementation to maintain limited BW gain (LGAIN), 2) supplementation to promote moderate BW gain (MGAIN), or 3) supplementation to promote elevated BW gain (HGAIN). Heifers were maintained in 2 pastures (36 heifers/pasture, 12 heifers/treatment in each pasture) with free-choice alfalfa-grass hay, and supplements were offered individually 6 d per week. Heifer shrunk BW was recorded on days -6 and 183 for average daily gain (ADG) calculation. Blood samples were collected for puberty evaluation via plasma progesterone weekly from days 0 to 182. On day 183, heifers were combined into a single group and received the same nutritional management until the end of the experimental period (day 718). From days 183 to 253, heifers were assigned to a fixed-time artificial insemination program combined with natural service. Average daily gain from days 0 to 182 was greater (P < 0.01) in HGAIN vs. MGAIN and LGAIN (0.78, 0.60, and 0.37 kg/d, respectively; SEM = 0.02), and greater (P < 0.01) in MGAIN vs. LGAIN heifers. Puberty attainment by the beginning of the breeding season was also greater in HGAIN vs. MGAIN and LGAIN (87.5%, 62.5%, and 56.5%, respectively; SEM = 7.1) but similar (P = 0.68) between MGAIN vs. LGAIN heifers. A treatment × day interaction was detected (P < 0.01) for calving rate, as HGAIN heifers calved earlier compared with MGAIN and LGAIN heifers. Ten heifers per treatment were assessed for milk production via weigh-suckle-weigh at 56.8 ± 1.5 d postpartum, followed by milk sample collection 24 h later. No treatment differences were detected (P ≥ 0.16) for milk yield and composition. However, mRNA expression of GLUT1 in milk fat globules was less (P ≤ 0.02) in LGAIN vs. MGAIN and HGAIN heifers, and expression of GLUT8 mRNA was also less (P = 0.04) in LGAIN vs. HGAIN heifers. No treatment differences were detected (P ≥ 0.44) for offspring weaning BW. Collectively, results from this experiment indicate that HGAIN hastened the reproductive development of replacement heifers, without negatively affecting their milk productivity and offspring weaning weight as primiparous cows.

The Notch system during pubertal development of the bovine mammary gland

The development of the mammary gland of cows during pre-weaning and puberty will condition its future productive capacity and warrants special study. In this respect, Notch signaling regulates tissue development and fate by modifying cell proliferation and differentiation and has been involved in stem cell maintenance, but has not been extensively studied in the developing mammary glands in cows. We therefore investigated Notch receptor expression and localization, as well as the expression of Notch ligands and target genes in the mammary gland of Holstein heifers in pre- and post-pubertal stages. Notch receptors 1 to 4 were detected by immunohistochemistry in the parenchyma and stroma of the developing gland. The subcellular localization of the four receptors was predominantly cytoplasmic except for NOTCH4, which was mostly nuclear. The membrane and the active intracellular domains of NOTCH paralogues were identified by western blot. NOTCH1 and NOTCH2 active domains increased during pubertal stages while NOTCH3 and NOTCH4 active domains decreased, suggesting strikingly different involvement of NOTCH paralogues in bovine mammary gland development and differentiation. The mRNA expression levels of the target genes HEY1 and HEY2 increased during peri-puberty whereas no variation of HES1 mRNA levels was observed. The mRNA levels of the Notch ligands JAGGED1 and DELTA1 also increased gradually during development. In conclusion, Notch signaling system dynamically varies throughout the development of the mammary gland during puberty pointing to specific time involvement of each component.

Characterization of miRNA profiles in the mammary tissue of dairy cattle in response to heat stress

Background

MicroRNAs (miRNAs) are a class of small noncoding RNAs that play important roles in the regulation of gene expression. However, the role of miRNAs in bovine mammary gland responses to heat stress is not well understood.

Results

In the present study, we performed a deep RNA sequencing analysis to identify miRNAs associated with the heat stress potential of the bovine mammary gland. We identified 27 miRNAs that were differentially expressed significantly between the mammary tissue of Holstein cattle heat stress and normal conditions. Twenty miRNAs had higher expression in the mammary tissue of heat-stressed Holstein cattle. The seven highest differentially expressed candidate miRNAs (bta-miR-21-5p, bta-miR-99a-5p, bta-miR-146b, bta-miR-145, bta-miR-2285 t, bta-miR-133a, and bta-miR-29c) identified by deep RNA sequencing were additionally evaluated by stem-loop qPCR. Enrichment analyses for targeted genes revealed that the major differences between miRNAs expression in the mammary gland of heat-stressed versus control were associated with the regulation of Wnt, TGF-β, MAPK, Notch, and JAK-STAT.

Conclusions

These data indicated that the differentially expressed miRNAs identified in this study may act as dominant regulators during heat stress. We might reduce heat stress damage of Holstein cows by up-regulating or down-regulating these differentially expressed miRNAs.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5298-1) contains supplementary material, which is available to authorized users.

STAT6, PBX2, and PBRM1 Emerge as Predicted Regulators of 452 Differentially Expressed Genes Associated With Puberty in Brahman Heifers

The liver plays a central role in metabolism and produces important hormones. Hepatic estrogen receptors and the release of insulin-like growth factor 1 (IGF1) are critical links between liver function and the reproductive system. However, the role of liver in pubertal development is not fully understood. To explore this question, we applied transcriptomic analyses to liver samples of pre- and post-pubertal Brahman heifers and identified differentially expressed (DE) genes and genes encoding transcription factors (TFs). Differential expression of genes suggests potential biological mechanisms and pathways linking liver function to puberty. The analyses identified 452 DE genes and 82 TF with significant contribution to differential gene expression by using a regulatory impact factor metric. Brain-derived neurotrophic factor was observed as the most down-regulated gene (P = 0.003) in post-pubertal heifers and we propose this gene influences pubertal development in Brahman heifers. Additionally, co-expression network analysis provided evidence for three TF as key regulators of liver function during pubertal development: the signal transducer and activator of transcription 6, PBX homeobox 2, and polybromo 1. Pathway enrichment analysis identified transforming growth factor-beta and Wnt signaling pathways as significant annotation terms for the list of DE genes and TF in the co-expression network. Molecular information regarding genes and pathways described in this work are important to further our understanding of puberty onset in Brahman heifers.

Polymorphism in promoter region of growth hormone receptor is associated with potential production capacity of insulin-like growth factor-1 in pre-pubertal Holstein heifers

Insulin-like growth factor-1 (IGF-1) is one of the important factors for growth, milk production and reproductive functions and mainly released from the liver in response to growth hormone (GH) via GH receptor (GHR) in cattle. Recently, some single nucleotide polymorphisms (SNPs) were identified in the bovine GHR gene. Some GHR-SNPs were shown to be related to plasma IGF-1 concentration in cattle. Hence, the capacity to IGF-1 production in the liver might be affected by GHR-SNP and associated with performance in the future. This study examined whether GHR-SNP is associated with IGF-1 production in the liver of pre-pubertal heifers. In 71 Holstein calves, blood samples for genomic DNA extraction were obtained immediately after birth. To genotype the GHR-SNPs in the promoter region, polymerase chain reaction (PCR) products were digested with restriction enzyme NsiI (cutting sites: AA, AG and GG). All heifers at 4 months of age were intramuscularly injected with 0.4 mg oestradiol benzoate. Blood samples were obtained from the jugular vein just before (0 h) and 24 h after injection. The number of AA, AG and GG at the NsiI site was 0, 17 and 54 respectively. In AG and GG, plasma GH concentrations were higher pre-injection than 24 h post-injection (p < 0.01). Moreover, plasma GH concentrations in AG post-injection were higher than in GG (p < 0.05). In contrast, the GG genotype exhibited higher plasma IGF-1 concentrations in pre-injection than post-injection (p < 0.01), although oestradiol did not change IGF-1 concentration in the AG genotype. We conclude that the GG polymorphism in the promoter region of GHR is associated with a higher potential capacity of IGF-1 production in the liver of cattle.

Tamoxifen impairs prepubertal mammary development and alters expression of estrogen receptor α (ESR1) and progesterone receptors (PGR)

Research has shown that prepubertal heifers experience allometric mammary growth that is influenced by the ovaries. Our purpose was to determine the role of estrogen in prepubertal mammary gland development. Sixteen Holstein calves were randomly assigned to 1 of 2 treatment groups: tamoxifen-injected (TAM) or control (CON). Calves were administered the antiestrogen tamoxifen (0.3 mg kg(1) d(1)) or placebo from 28 to 120 d of age. At 120 d, calves were euthanized and udders removed. Weight and DNA content of trimmed parenchymal tissue were halved (P ≤ 0.0001) in TAM compared with CON calves. Parenchymal samples from 3 zones of the left rear mammary gland (lower, middle, and outer regions) were processed for immunohistochemical staining for estrogen receptor α (ESR1) and progesterone receptor (PGR), Ki67-positive cells, and 5-bromo-2'-deoxyuridine label retaining cells (LRCs). Overall, neither the percentage nor location within the epithelial tissue layer of either ESR1- or PGR-positive cells was impacted by TAM treatment. However, image analysis indicated a 6.2-fold lower (P = 0.0001) level of ESR1 protein expression in TAM calves. Similarly, messenger RNA expression of ESR1 was also reduced (P = 0.0001) in TAM heifers. In contrast, expression of PGR protein was greater by 43% (P = 0.03) in TAM calves, but messenger RNA expression did not differ between treatments. Overall, TAM calves had a higher (P ≤ 0.03) percentage and density (cells per tissue area) of Ki67-positive cells. Irrespective of treatment, there were also more Ki67-labeled cells in the outer zones of the mammary gland (P ≤ 0.001). We were able to effectively use multispectral imaging to identify positive cells and quantify the expression of ESR1 and PGR protein. We also identified and counted the proportion of label retaining cells (LCR) (putative epithelial stem cells). We noted an overall 2.9-fold greater number of LRCs in TAM heifers and more LRCs in the outer sampling zones. This suggests that a cohort of LCR cells in TAM remained inactivated in comparison with CON heifers, which exhibited markedly increased growth of the mammary parenchymal tissue over the treatment period. These results suggest that the impacts of ovariectomy are partially explained by loss of ESR1 expression and/or estrogen receptor signaling in the prepubertal bovine mammary gland. The significance of mammary expression of PGR in control of prepubertal bovine mammary development remains unresolved.

Responses of the mammary transcriptome of dairy cows to altered photoperiod during late gestation

Cows exposed to short day photoperiod (SD, 8L:16D) during the 60-day nonlactating period prior to parturition produce more milk in their subsequent lactation compared with cows exposed to long day photoperiod (LD, 16L:8D). Although this response is well established in dairy cows, the underlying mechanisms are not understood. We hypothesized that differential gene expression in cows exposed to SD or LD photoperiods during the dry period could be used to identify the functional basis for the subsequent increase in milk production during lactation. Pregnant, multiparous cows were maintained on an SD or LD photoperiod for 60 days prior to parturition. Mammary biopsies were obtained on days -24 and -9 relative to parturition and Affymetrix GeneChip Bovine Genome Arrays were used to quantify gene expression. Sixty-four genes were differentially expressed (P ≤ 0.05 and fold-change ≥ |1.5|) between SD and LD treatments. Many of these genes were associated with cell growth and proliferation, or immune function. Ingenuity Pathway Analysis predicted upstream regulators to include TNF, TGF-β1, interferon-γ, and several interleukins. In addition, expression of 125 genes was significantly different between day -24 and day -9; those genes were associated with milk component metabolism and immune function. The interaction of photoperiod and time affected 32 genes associated with insulin-like growth factor I signaling. Genes differentially expressed in response to photoperiod were associated with mammary development and immune function consistent with the enhancement of milk yield in the ensuing lactation. Our results provide insight into the mechanisms by which photoperiod affects the mammary gland and subsequently lactation.

Ovariectomy in young prepubertal dairy heifers causes complete suppression of mammary progesterone receptors

Mammary growth and development depends on ovarian steroids and particularly interaction of estrogen and progesterone with their intracellular receptors. The objectives of this study were to determine the effect of ovariectomy on the expression of protein and messenger RNA for estrogen receptor-alpha (ESR1) and progesterone receptor (PGR) and their relation to mammary ductal development and cell proliferation. Prepubertal Holstein heifers 2, 3, or 4 mo of age were randomly assigned to one of 2 treatments, ovariectomized (OVX; n = 8) or sham operated (INT; n = 12). Mammary parenchymal (PAR) tissue samples were harvested 30 d after surgery. Localization and quantitation of ESR1 and PGR in PAR were determined by immunohistochemistry and quantitative multispectral imaging. Relative messenger RNA expression of ESR1 and PGR in PAR was measured by quantitative real time polymerase chain reaction. We observed the complete absence of PGR-positive epithelial cell nuclei and reduced PGR transcript abundance in mammary parenchyma of OVX heifers. The percent of epithelial cells expressing ESR1 did not differ by treatment but was decreased with age. However, average intensity of ESR1 expression per cell was reduced in OVX heifers. The abundance of Ki67 labeled epithelial cells and stromal cells was reduced after ovariectomy. These data suggest that reduced mammary development after ovariectomy may be mediated by loss of PGR expression and reduced ESR1 expression in positive cells. A presumptive relationship with ovarian-derived circulating estradiol remains unresolved, but data suggest other ovarian-derived agents may play a role. Use of specific antagonists to manipulate expression or action of PGR and ESR1 receptors should provide direct evidence for roles of these receptors in prepubertal bovine mammary development.

Cellular proliferation rate and insulin-like growth factor binding protein (IGFBP)-2 and IGFBP-3 and estradiol receptor alpha expression in the mammary gland of dairy heifers naturally infected with gastrointestinal nematodes during development

Mammary ductal morphogenesis during prepuberty occurs mainly in response to insulin-like growth factor-1 (IGF-1) and estradiol stimulation. Dairy heifers infected with gastrointestinal nematodes have reduced IGF-1 levels, accompanied by reduced growth rate, delayed puberty onset, and lower parenchyma-stroma relationship in their mammary glands. Immunohistochemical studies were undertaken to determine variations in cell division rate, IGF-1 system components, and estradiol receptors (ESR) during peripubertal development in the mammary glands of antiparasitic-treated and untreated Holstein heifers naturally infected with gastrointestinal nematodes. Mammary biopsies were taken at 20, 30, 40, and 70 wk of age. Proliferating cell nuclear antigen immunolabeling, evident in nuclei, tended to be higher in the parenchyma of the glands from treated heifers than in those from untreated. Insulin-like growth factor binding proteins (IGFBP) type 2 and type 3 immunolabeling was cytoplasmic and was evident in stroma and parenchyma. The IGFBP2-labeled area was lower in treated than in untreated heifers. In the treated group, a maximal expression of this protein was seen at 40 wk of age, whereas in the untreated group the labeling remained constant. No differences were observed for IGFBP3 between treatment groups or during development. Immunolabeling for α ESR (ESR1) was evident in parenchymal nuclei and was higher in treated than in untreated heifers. In the treated group, ESR1 peaked at 30 wk of age and then decreased. These results demonstrate that the parasite burden in young heifers negatively influence mammary gland development, affecting cell division rate and parameters related to estradiol and IGF-1 signaling in the gland.

Changes in mammary secretory tissue during lactation in ovariectomized dairy cows

In dairy animals, the milk yield (MY) changes during a lactation and is influenced by several physiological, livestock management and environmental factors. The MY produced by a mammary gland depends on synthetic activity of mammary epithelial cells (MECs) as well as MEC number and mammary secretory tissue organization. It has been suggested that ovarian steroids (estradiol and progesterone) have a negative effect on MY in lactating cows. In a previous study, we showed that the suppression of ovarian secretions by an ovariectomy improved lactation persistency in dairy cows. Here we were interested in the effects of ovariectomy on plasma estradiol and progesterone concentrations and on changes that occur in mammary secretory tissue during lactation. We demonstrated that the ovariectomy of lactating cows at the time of the lactation peak induced a rapid and dramatic drop in plasma progesterone and a smaller reduction in plasma estradiol. Interestingly, the study of the changes in mammary secretory tissue over time revealed that the improvement of MY measured in the ovariectomized cows was associated with a limited increase in estradiol receptivity in MECs, a reduced mammary tissue remodeling and reduced blood protein concentration in milk, in late lactation. These results suggest that ovarian secretions, particularly estradiol and progesterone, act to enhance processes for mammary gland involution in late-lactating dairy cows.

A proteomic analysis of the effect of growth hormone on mammary alveolar cell-T (MAC-T) cells in the presence of lactogenic hormones

The bovine mammary alveolar cell-T (MAC-T) cell line is able to uniformly differentiate and secrete casein proteins in response to dexamethasone, insulin, and prolactin and is extensively used to study bovine mammary epithelial cell (MEC) function. Somatotropin, or growth hormone (GH), has been shown to increase milk protein synthesis both in vivo and in mammary cell models and to induce cytoskeletal rearrangement in a 3T3 fibroblast cell line and a Chinese hamster ovary cell line. To identify the nature of the effects of GH in MECs cultured with lactogenic hormones, changes in global protein expression were assessed in the MAC-T cell line with the use of two-dimensional gel electrophoresis and matrix-assisted laser desorption ionization tandem time of flight mass spectrometry. Forty proteins were differentially expressed in response to GH (P < 0.05) and were related to metabolism, the cytoskeleton, protein folding, RNA and DNA processing, and oxidant stress. These widespread changes in protein expression are indicative of a global role of GH in overall cellular differentiation that may underlie the direct modulation of milk component synthesis in MEC models that have been described to date.

Effect of staged ovariectomy on measures of mammary growth and development in prepubertal dairy heifers

Previous studies in prepubertal heifers suggest that the magnitude of reduction in mammary parenchymal growth in response to ovariectomy varies with the age at which surgery is performed. We hypothesized that ovarian secretions are essential for initiating mammary development but not required to maintain allometric mammary growth in prepubertal dairy heifers. The objectives of this study were to determine the effect of staged ovariectomy during the prepubertal period on mammary growth and tissue composition and the expression of selected genes. Prepubertal Holstein heifers at 2, 3 or 4 months of age were randomly assigned to one of two treatments, ovariectomized (OVX; n = 12) or sham operated (INT; n = 12). Mammary parenchyma (PAR) and fat pad (MFP) were harvested 30 days after surgery. Proximate composition of PAR and MFP (DNA, protein and lipid) as well as expression of the selected estrogen-responsive genes stanniocalcin1 (STC1), tissue factor pathway inhibitor precursor (TFPI) and proliferating cell nuclear antigen (PCNA) were determined in PAR and MFP by quantitative real-time PCR. The relative amount of epithelium and proportion of epithelia cell nuclei expressing the proliferation marker Ki67 were determined by histological and immunohistochemical analyses, respectively. MFP mass was not impacted by treatment but was decreased with age as was lipid content and concentration (P ⩽ 0.01). The mass of mammary PAR was reduced in OVX and increased with age (P ⩽ 0.01). Parenchymal tissue tended to have less total DNA, protein and lipid in OVX heifers. Parenchymal tissue concentrations of protein and DNA were increased with age and there was an age × treatment interaction. Treatment had no effect on either the Ki67 labeling index or percent epithelial area. The relative abundances of STC1, TFPI and PCNA mRNA in PAR were reduced in OVX. We did not find a significant impact of ovariectomy on mRNA expression when surgery was performed at 2 months compared with surgery at 3 or 4 months of age. However, having nearly undetectable PAR in two heifers ovariectomized at the earliest period (2 months of age) suggests that early ovariectomy is especially detrimental to subsequent parenchymal development.

Suppression of ovarian secretions before puberty strongly affects mammogenesis in the goat

The objective of this study was to provide insight into the biological mechanisms underlying mammary development and the role of the ovaries in prepubertal caprine mammogenesis using a serial ovariectomy approach. Young Alpine goats were ovariectomized (Ovx) or sham-operated (Int) at three periods before puberty (G1=1 month, G2=2 month and G3=3 months of age) and one after puberty (G7=7 months of age). The goats were slaughtered at 9 months of age and mammary glands were removed. Ovariectomy performed at 1, 2 and 3 months of age caused a 50% reduction in DNA concentration, in mammary tissue taken from the parenchyma-stroma border region. Morphological analysis of mammary tissue sections indicated that the parenchymal structures of Ovx goats were negatively affected by ovariectomy. Goats ovariectomized before 2 months of age (Ovx-1 and Ovx-2) showed a significant decrease in the percent of cells proliferating in mammary glands of 9-month old goats (proliferating cell nuclear antigen expression and antigen Ki67-positive cell number). Also, goats ovariectomized at 1 and 2 months of age had reduced matrix metalloprotease 2 activity at 9 months of age. E-cadherin was strongly decreased in goats ovariectomized before 2 months of age (80 and 85% in Ovx-1 and Ovx-2 goats, respectively). Quantitative PCR analysis of transcripts encoding for oestrogen (ERα) and progesterone receptors (PR) and immunodetection of ERα showed that ovariectomy at 1 and 2 months of age strongly inhibited the transcription of ERα and PR in the mammary gland. We conclude that ovariectomy before 3 months of age markedly impaired parenchymal development. These findings suggest that prepubertal mammogenesis in goats depends on the ovaries to initiate mammary epithelial cell proliferation and mammary gland remodelling.

Functional and gene network analyses of transcriptional signatures characterizing pre-weaned bovine mammary parenchyma or fat pad uncovered novel inter-tissue signaling networks during development

BACKGROUND

The neonatal bovine mammary fat pad (MFP) surrounding the mammary parenchyma (PAR) is thought to exert proliferative effects on the PAR through secretion of local modulators of growth induced by systemic hormones. We used bioinformatics to characterize transcriptomics differences between PAR and MFP from approximately 65 d old Holstein heifers. Data were mined to uncover potential crosstalk through the analyses of signaling molecules preferentially expressed in one tissue relative to the other.

RESULTS

Over 9,000 differentially expressed genes (DEG; False discovery rate <or= 0.05) were found of which 1,478 had a >or=1.5-fold difference between PAR and MFP. Within the DEG highly-expressed in PAR vs. MFP (n = 736) we noted significant enrichment of functions related to cell cycle, structural organization, signaling, and DNA/RNA metabolism. Only actin cytoskeletal signaling was significant among canonical pathways. DEG more highly-expressed in MFP vs. PAR (n = 742) belong to lipid metabolism, signaling, cell movement, and immune-related functions. Canonical pathways associated with metabolism and signaling, particularly immune- and metabolism-related were significantly-enriched. Network analysis uncovered a central role of MYC, TP53, and CTNNB1 in controlling expression of DEG highly-expressed in PAR vs. MFP. Similar analysis suggested a central role for PPARG, KLF2, EGR2, and EPAS1 in regulating expression of more highly-expressed DEG in MFP vs. PAR. Gene network analyses revealed putative inter-tissue crosstalk between cytokines and growth factors preferentially expressed in one tissue (e.g., ANGPTL1, SPP1, IL1B in PAR vs. MFP; ADIPOQ, IL13, FGF2, LEP in MFP vs. PAR) with DEG preferentially expressed in the other tissue, particularly transcription factors or pathways (e.g., MYC, TP53, and actin cytoskeletal signaling in PAR vs. MFP; PPARG and LXR/RXR Signaling in MFP vs. PAR).

CONCLUSIONS

Functional analyses underscored a reciprocal influence in determining the biological features of MFP and PAR during neonatal development. This was exemplified by the potential effect that the signaling molecules (cytokines, growth factors) released preferentially (i.e., more highly-expressed) by PAR or MFP could have on molecular functions or signaling pathways enriched in the MFP or PAR. These bidirectional interactions might be required to coordinate mammary tissue development under normal circumstances or in response to nutrition.

Nanowire-based delivery of Escherichia coli O157 shiga toxin 1 A subunit into human and bovine cells

Silica nanowires (NWs) were used to introduce the Shiga toxin type 1 A subunit (StxA1) into cultured bovine and human epithelial cells. We extended technology developed in our laboratories that employs fibronectin (Fn) to induce integrin-mediated uptake of NWs by coating NWs with StxA1 and Fn. The bonding strengths of Fn and StxA1 to the surface of NWs were measured by X-ray photoelectron spectroscopy. This technique demonstrated complex interactions between Fn, StxA1, and the NWs. Neutral red cytotoxicity assays and field emission scanning electron microscopy confirmed that the NW-StxA1-Fn complexes were effectively internalized and caused cell death. This indicates that NWs can carry StxA1 and potentially other toxic or therapeutic agents into eukaryotic cells. Ongoing studies include improved functionalizing of NWs aimed at increasing internalization efficiency and substituting ligands for specific cell targeting.