Abstract
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.
Highlights
It has been stated that the future milk yield potential of cows depends on the optimum development of the mammary parenchyma that is established during growth, starting as early as the first weeks of life[1,2]
NOTCH1–3 are predominantly expressed in the cytoplasm while NOTCH4 is almost exclusively expressed in the nucleus
The four Notch receptor paralogues were identified in the mammary gland of developing dairy heifers and their histological and subcellular localization described
Summary
It has been stated that the future milk yield potential of cows depends on the optimum development of the mammary parenchyma that is established during growth, starting as early as the first weeks of life[1,2]. The mammary gland undergoes repeated cycles of development and involution coordinated with pregnancy and lactation cycles This process of growth and regression points to a hierarchy of stem and progenitor cells that are able to regenerate specialized populations of mammary epithelial and myoepithelial cells. With the perspective of understanding all insights of the regulation of mammary development during puberty which will impact on performance of the future gland in adulthood, we investigated the expression and localization of the four Notch receptor paralogues, as well as the expression of two ligands and three target genes in the bovine mammary gland before, during and after puberty onset
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