Expression of alpha-lactalbumin, alpha-S1-casein, and lactoferrin genes is heterogeneous in sheep and cattle mammary tissue.

Abstract

We used 35S-labeled cRNA probes to localize the sites of a-lactalbumin, a-Sl-casein, and laaoferrin mRNA synthesis in sheep and forcibly weaned cattle mammary tissue. Expression of a-lactalbumin was absent in three of four "virgin" glands studied, present in some alveoli of "pregnant" glands but not in others, despite a similar histological appearance. In the early lactating gland, expression was high in those alveoli with few fat globules in their cells and lumen and was absent in alveoli with abundant fat globules. These observations suggest either that a-lactalbumin gene expression is linked to the long-term seaetory activity of cells and falls once cells are resting or regressing, or that there are cyclical variations in expression, or that in the lactating IntroductionThe mammary gland is a complex organ both in structure and function. After pubertal mammogenesis it undergoes three physiological transitions during a lactation cycle: from involution to colostrogenesis, to lactation, then back to involution. Marked changes occur in mammary gland size, structure, and secretion as the gland progresses to or from a state of active milk synthesis (33). An obvious question to ask is what happens to the expression of various milk protein genes during this time, and several investigators have indeed performed such studies (3,27,28,39). In general, the methodology has been based on the extraction ofmRNA from total mammary tissue so that the levels of gene expression being measured are actually the average for the whole tissue, and heterogeneities would not be detected. More recently in situ hybridization has been used, and although this is capable of detecting tissue-to-tissue and cell-to-cell variations in gene expression, the detection of such differential expression per se does not seem to have been the primary aim of most investigators. For example, a study of a-casein (21) neither set out to detect nor to comment on variations in mRNA levels throughout the mouse mammary gland.Correspondence t~: Adrian Molenaar, Molecular Biology, MAFTech, Ruakura Agricultural Centre, Hamilton, New Zealand. gland some groups of epithelial cells are synthesizing a-lactalbumin and some are synthesizing fat. Enpression patterns of adl-casein were similar to those of a-lactalbumin. Lactoferrin, in contrast, was expressed almost exclusively in the "fatty alveoli" of both species. Our results show that dramatic variations in milk gene expression can OCCUI throughout the mammary gland of sheep and cattle and that at no stage of pregnancy, lactation, or involution can the gland be considered metabolically homogeneous. (J I-iiktochem Cytochem 40:611418, 1992) KEY WORDS: Mammary; Milk proteins; a-lactalbumin; a-S1-casein; Lactoferrin; In situ hybridization; mRNA expression; Localization; Ovine; Bovine.The present study is aimed explicitly at addressing the possibility of heterogeneous expression of milk protein genes in the mammary glands of ruminants. We have chosen ruminants for three reasons: first, their economic importance; second, th...

Mammary transcriptome analysis of lactating dairy cows following administration of bovine growth hormone

“…The positive correlation between SLC34A2 mRNA abundance and the yield of milk, protein, lactose and fat is suggestive of increased milk output. Interestingly, the mammary gland of lactating dairy cows show heterogeneity in the proportion of differentiated, actively secreting cells (Molenaar et al, 1992), and SLC34A2 protein is a marker of differentiated milk-secreting mammary alveolar cells in mice (Shillingford et al, 2003). In addition, the protein encoded by SLC34A2, which is a sodium dependent membrane transporter that imports phosphate into the cell, is activated by the nutrient sensing mTOR protein in Xenopus ooyctes (Shojaiefard and Lang, 2006).…”

Association of polymorphism within LTF gene promoter with lactoferrin concentration in milk of Holstein cows

“…Therefore, it is thought that polymorphonuclear leukocytes are the source of lactoferrin in milk, especially during stimulation of the immune system. The elevation of LTF mRNA expressed in udder tissue during mastitis (Schmitz et al 2004, Griesbeck-Zilch et al 2008 proved the that LTF in the udder also originates from the secretory epithelium (Molenaar et al 1992, Pfaffl et al 2003, Zheng et al 2005.…”

The effect of level of feeding, genetic merit, body condition score and age on biological parameters of a mammary gland model

“…The reactivation of quiescent alveoli, k 4 , was greatest in animals of 5 to 8 years of age. The exact mechanisms by which quiescent alveoli are reactivated into secretory alveoli is not certain (Molenaar et al, 1992). Reactivation of quiescent alveoli may be lower in two-year-old animals than 5-to 8-year-old animals because the former are often still partitioning energy towards growth i.e.…”

“…Yields of milk in dairy cattle and other species are largely a function of the number of mammary secretory cells and the secretory activity per cell (Knight, 1989 andDijkstra et al, 1997;Capuco et al, 2001). The numbers of active secretory mammary cells at different stages of the lactation are determined by the balance between the rates of proliferation and quiescence into non-secretory cells (Molenaar et al, 1992;Knight, 2000). Proliferation, the process where undifferentiated mammary cells progress to an active secretory state, occurs at an exponential rate from the start of gestation and reaches a maximum soon after parturition when mammary cell numbers are at their peak (Knight, 1993).…”

“…Shortly after parturition, a proportion of mammary cells progress to a quiescent or resting pool of non-secretory mammary cells. These quiescent cells can either be reactivated to milksecreting mammary cells, or they can proceed to senescence which is often termed apoptosis (Molenaar et al, 1992;Wilde et al, 1997).…”