Analysis of inhibitor of apoptosis protein family expression during mammary gland development

Background  

Inhibitors-of-Apoptosis-Proteins (IAPs) are an evolutionarily conserved family of proteins capable of regulating several facets of apoptosis. IAPs are frequently dysregulated in cancer, but their role in the regulation of apoptosis during developmental processes is not fully understood. Here we examined the expression of IAPs during the post-natal development of the mouse mammary gland, which is a tissue that exhibits a profound induction of apoptosis during involution.     

Microarray analysis of gene expression profiles in the bovine mammary gland during lactation

Mammary glands undergo functional and metabolic changes during virgin, lactation and dry periods. A total of 122 genes were identified as differentially expressed, including 79 up-regulated and 43 down-regulated genes during lactation compared with virgin and dry periods. Gene ontology analysis showed the functional classification of the up-regulated genes in lactation, including transport, biosynthetic process, signal transduction, catalytic activity, immune system process, cell death, and positive regulation of the developmental process. Microarray data clarified molecular events in bovine mammary gland lactation.     

microRNAs and the mammary gland: A new understanding of gene expression

MicroRNAs (miRNAs) have been identified in cells as well as in exosomes in biological fluids such as milk. In mammary gland, most of the miRNAs studied have functions related to immunity and show alterations in their pattern of expression during lactation. In mastitis, the inflammatory response caused by Streptococcus uberis alters the expression of miRNAs that may regulate the innate immune system. These small RNAs are stable at room temperature and are resistant to repeated freeze/thaw cycles, acidic conditions and degradation by RNAse, making them resistant to industrial procedures. These properties mean that miRNAs could have multiple applications in veterinary medicine and biotechnology. Indeed, lactoglobulin-free milk has been produced in transgenic cows expressing specific miRNAs. Although plant and animal miRNAs have undergone independent evolutionary adaptation recent studies have demonstrated a cross-kingdom passage in which rice miRNA was isolated from human serum. This finding raises questions about the possible effect that miRNAs present in foods consumed by humans could have on human gene regulation. Further studies are needed before applying miRNA biotechnology to the milk industry. New discoveries and a greater knowledge of gene expression will lead to a better understanding of the role of miRNAs in physiology, nutrition and evolution.     

Down-regulation of protein tyrosine phosphatase gene expression in lactating mouse mammary gland

Detailed analysis of protein tyrosine phosphatase (PTP) expression in mouse mammary gland and mammary epithelial cells using a set of degenerate primers corresponding to the PTP core domain sequence revealed the presence of 16 different receptor-type and intracellular PTPs. Northern blot and RT-PCR analyses revealed that some PTPs were up-regulated during gestation, suggesting that these enzymes are involved in development of mammary gland. However, expression of most PTPs dramatically decreased during lactation, whereas the beta-casein gene expression was increased and remained at a high level. At the involution stage after weaning, most PTPs were up-regulated and their expression returned almost to the virgin level. Such up-regulation was also induced by forced weaning in lactating mother mice. These results suggest the possible contribution of PTPs to the development, involution, and remodeling of mammary gland and their possible inhibitory action on maintaining high expression of milk genes during lactation.     

Cre-mediated gene deletion in the mammary gland.

To delete genes specifically from mammary tissue using the Cre-lox system, we have established transgenic mice expressing Cre recombinase under control of the WAP gene promoter and the MMTV LTR. Cre activity in these mice was evaluated by three criteria. First, the tissue distribution of Cre mRNA was analyzed. Second, an adenovirus carrying a reporter gene was used to determine expression at the level of single cells. Third, tissue specificity of Cre activity was determined in a mouse strain carrying a reporter gene. In adult MMTV-Cre mice expression of the transgene was confined to striated ductal cells of the salivary gland and mammary epithelial cells in virgin and lactating mice. Expression of WAP-Cre was only detected in alveolar epithelial cells of mammary tissue during lactation. Analysis of transgenic mice carrying both the MMTV-Cre and the reporter transgenes revealed recombination in every tissue. In contrast, recombination mediated by Cre under control of the WAP gene promoter was largely restricted to the mammary gland but occasionally observed in the brain. These results show that transgenic mice with WAP-Cre but not MMTV-Cre can be used as a powerful tool to study gene function in development and tumorigenesis in the mammary gland.     

Induction of osteopontin gene expression during mammary gland involution and effects of glucocorticoid on its expression in mammary epithelial cells

To understand the molecular mechanisms of mammary gland involution, an involution-induced clone was identified from a cDNA library of mouse mammary gland by differential screening. Characterization of a clone by sequencing and northern analysis showed that expression of the osteopontin gene was induced during involution of mouse mammary gland. But induction of the osteopontin gene was not observed in apoptotic HC11 mammary epithelial cells under serum starvation. In HC11 cells, dexamethasone treatment from the seeding stage showed five-fold induction of osteopontin gene expression, but the expression was not changed when dexamethasone was added to confluent cells.     

牦牛SND1基因特征序列分析及其蛋白在乳腺的表达

Staphylococcal nuclease and tudor domain containing 1（ SND1,Tudor-SN）是一种参与基因调控的转录共激活因子蛋白,本研究意在克隆牦牛泌乳相关基因SND1,分析其生物特性,研究其蛋白在乳腺的表达。采集牦牛泌乳期乳腺组织,胰蛋白酶消化法得到原代乳腺上皮细胞,纯化到3代, 采用RT-PCR扩增克隆SND1基因,测序并拼接,并用相关生物信息软件分析牦牛SND1基因特性;用免疫组织化学和免疫荧光技术对牦牛SND1基因编码蛋白进行定位分析。获得如下结果：牦牛SND1基因全序列为3294 bp,含有2733 bp的ORF,共包含20种氨基酸。SND1基因编码蛋白为非分泌蛋白,非跨膜蛋白;同源性分析显示,牦牛SND1基因与野牛、家牛、藏羚羊、山羊、猪、野骆驼、马、黑猩猩、人、褐家鼠的同源性分别为99%、98%、96%、94%、91%、90%、90%、89%、89%、85%;系统进化树表明与野牛和家牛的进化水平较近,与人和鼠的进化水平较远。免疫组织化学染色结果显示,SND1蛋白在分泌上皮细胞（乳腺上皮细胞）和导管上皮细胞呈阳性高表达,在肌上皮细胞呈弱表达。免疫荧光显示,SND1蛋白在乳腺上皮细胞胞核高表达,胞质弱表达。上述研究结果为进一步探究SND1对牦牛泌乳机能的调节提供了相关依据,也为高寒哺乳动物的研究提供了参考资料。     

Structure of the rabbit tc-casein encoding gene: expression of the cloned gene in the mammary gland of transgenic mice

The rabbit κ-casein (κ-Cas) encoding gene has been isolated as a series of overlapping DNA fragments cloned from a rabbit genomic library constructed in bacteriophage λEMBL3. The clones harboured the 7.5-kb gene flanked by about 2.1 kb upstream and 9 kb downstream sequences. The cloned gene is the most frequently occurring of two κ-Cas alleles identified in New Zealand rabbits. Comparison of the corresponding domains in rabbit and bovine κ-Cas shows that both genes comprise 5 exons and that the exon/intron boundary positions are conserved whereas the introns have diverged considerably. The first three introns are shorter in the rabbit, the second intron showing the greatest difference between the two species: 1.35 kb instead of 5.8 kb in the bovine gene. Repetitive sequence motives reminiscent of the rabbit C type repeat and the complementary inverted C type repeat were identified in the fourth and first introns, respectively. Transgenic mice were produced by microinjecting into mouse oocytes an isolated genomic DNA fragment which contained the entire κ-Cas coding region, together with 2.1-kb 5′ and 4.0-kb 3′ flanking region. Expression of transgene rabbit κ-Cas mRNA could be detected in the mammary gland of lactating transgenic mice and the production of rabbit κ-Cas was detected in milk using species-specific antibodies. The cloned gene is thus functional.     

Targeting expression to the mammary gland: intronic sequences can enhance the efficiency of gene expression in transgenic mice

We are studying the tissue-specific expression of the sheep milk-whey protein gene, β-lactoglobulin. We have used sequences derived from this gene to target the expression of biomedical proteins into milk with the intention to exploit this technology in transgenic sheep as a means of protein production. In the present study, a series of β-lactoglobulin hybrid genes and β-lactoglobulin minigenes were evaluated for expression in the mammary gland of transgenic mice. In particular, we have assessed whether there is a requirement for introns for efficient transgene expression in the mammary gland, since the coding sequences of many candidate proteins are available only as cDNAs. The results suggest that the inclusion of natural introns in constructs can enhance the efficiency of transgene expression. Thus, a hybrid construct comprising 4.3 kb of the immediate 5′ flanking sequences of β-lactoglobulin fused to a genomic minigene encoding human α-antitrypsin (α₁AT) was expressed much more efficiently than an α₁AT-cDNA construct containing the same β-lactoglobulin segment. Similarly, the intact β-lactoglobulin gene was expressed more efficiently than the corresponding intronless β-lactoglobulin minigene. This effect was not seen in transient expression expriments in baby hamster kidney cells when β-lactoglobulin-α₁AT constructs were driven by SV40 enhancer sequences. The effect cannot be explained by a simple requirement for splicing, since the inclusion of the first β-lactoglobulin intron into cDNA constructs encoding human α₁AT or β-lactoglobulin itself failed to enhance the efficiency of transgene expression. It is concluded that sequence elements within introns may interact with the upstream 5′ flanking sequences of β-lactoglobulin and enable the latter to function efficiently in the mammary gland of transgenic mice.     

Oestrogen administration and the expression of the kallikrein gene family in the rat submandibular gland

Using a series of oligonucleotide probes (18-21 mers) specific for members of the rat kallikrein/tonin (arginyl-esteropeptidase) gene family (PS, S1, S2, S3, K1, P1), we have shown by Northern blot analysis that all six genes are expressed in the submandibular gland (SMG), with PS (true kallikrein) the most abundant in both male and female rats. Though female levels of PS mRNA are similar to that in the male, levels of mRNA from both the kallikrein-like (S1, K1, P1) and tonin (S2)/tonin-like (S3) genes are all substantially lower in the female than in the male rat. In contrast with the oestrogen dependence of anterior pituitary kallikrein (PS) gene expression, oestrogen administration (6 micrograms/day for 8 days) to castrate male or female rats is without effect on PS or S1, S2, S3, K1, P1 mRNA levels in the SMG. These findings suggest a tissue-specificity in the oestrogen regulation of true kallikrein gene expression in the two tissues. In intact male rats, oestrogen administration lowers SMG levels of S1, S2, S3, K1, and P1 but not PS mRNA to castrate levels, presumably by suppression of the pituitary/gonadal axis, consistent with the previously reported androgen dependence of SMG expression of these genes with the exception of PS.     

Persistent changes in gene expression induced by estrogen and progesterone in the rat mammary gland.

Epidemiological studies have consistently shown that an early full-term pregnancy is protective against breast cancer. We hypothesize that the hormonal milieu that is present during pregnancy results in persistent changes in the pattern of gene expression in the mammary gland, leading to permanent changes in cell fate that determine the subsequent proliferative response of the gland. To investigate this hypothesis, we have used suppression subtractive hybridization to identify genes that are persistently up-regulated in the glands of E- and progesterone (P)-treated Wistar-Furth rats 28 d after steroid hormone treatment compared with age-matched virgins. Using this approach, a number of genes displaying persistent altered expression in response to previous treatment with E and P were identified. Two markers have been characterized in greater detail: RbAp46 and a novel gene that specifies a noncoding RNA (designated G.B7). Both were persistently up-regulated in the lobules of the regressed gland and required previous treatment with both E and P for maximal persistent expression. RbAp46 has been implicated in a number of complexes involving chromatin remodeling, suggesting a mechanism whereby epigenetic factors responsible for persistent changes in gene expression may be related to the determination of cell fate. These results provide the first support at the molecular level for the hypothesis that hormone-induced persistent changes in gene expression are present in the involuted mammary gland.