To the IL-6 family of cytokines, is indispensable for self-renewal of

To the IL-6 family of cytokines, is indispensable for self-renewal of mouse embryonic stem cells (mESCs) and maintenance of their undifferentiated state [2]. LIF, after binding to the LIFR/gp130 heterodimer, can trigger three signalling pathways, namely JAK/Stat3, PI3K/Akt and SHP2/MAPK. However, the Stat3 branch of LIF signalling has been demonstrated to play a central role in the regulation of self-renewal and pluripotency of mESCs [3]. In fact, overexpression of a dominant negative variant of Stat3 in mESCs leads to loss of pluripotency and enhanced cell differentiation [4]. Furthermore, Stat3 activation is sufficient to maintain the undifferentiated state of mESCs, as demonstrated in a study using a fusion protein between Stat3 and the ligand binding domain of the estrogen receptor (ER) [5]. Additionally, deletion of Stat3 causes embryonic lethality as Stat32/ 2 embryos have reduced growth of the inner cell mass (ICM) and show rapid degeneration between days E6.5?E7.5 [6]. Thus, CreloxP systems have been used to investigate the role of Stat3 in different cell types. In the small intestine, Stat3 is absolutely required for AN 3199 site survival of the stem cells near the base of the crypt [7] and expression of dominant negative Stat3 in hematopoietic BIBS39 stemcells results in a reduced lympho-myeloid reconstituting ability [8]. In the mammary gland Stat3 is activated early during postlactational regression and is a major regulator of the extensive cell death and tissue remodelling that occurs during this process [9,10]. Recently, we demonstrated that activation of Stat3 is required during mammary gland involution to upregulate the expression of the lysosomal proteases, cathepsins B and L, and to downregulate the expression of their endogenous cytoplasmic inhibitor (Spi2A) thereby mediating cell death [11]. However, a potential role for Stat3 in mammary stem cells has not been determined. Mammary epithelium consists of luminal (ductal and alveolar) and basal (myoepithelial) cells that are organised into a bi-layered structure with luminal cells lining the lumen encased by an outer layer of basal cells [12]. It is presumed that both luminal and basal lineages originate from common embryonic stem and progenitor cells. Moreover, each pregnancy cycle is accompanied by the massive expansion of the mammary epithelial compartment which suggests that the adult mammary gland contains a population of stem/progenitor cells with long-term self-renewal potential [13]. Previous reports have confirmed that mammary stem cells transplanted into a cleared fat pad can regenerate a functional mammary epithelial tree [14,15,16,17]. Moreover, each full-term pregnancy cycle generates so called parity-induced mammary epithelial cells (PI-MECs) that produce milk proteins during late gestation and lactation and do not undergo programmed cell death 15826876 during involution. Some of these cells act as alveolar progenitors during subsequent pregnancies and in vivo transplantation experiments proved their multipotency and self renewalStat3 and Mammary Stem CellsFigure 1. Stat3fl/fl;BLG-Cre+ glands show incomplete involution and luminal progenitors have reduced proliferative capacity. (A) RTPCR analysis of Stat3 expression in FACS sorted populations of mammary epithelial cells. MRU: mammary repopulating units. (B, C) H E staining of sections of Stat3fl/fl;BLG-Cre2 and Stat3fl/fl;BLG-Cre+ mammary glands collected at day 5 of the second gestation (B) or four weeks after natural weaning (C).To the IL-6 family of cytokines, is indispensable for self-renewal of mouse embryonic stem cells (mESCs) and maintenance of their undifferentiated state [2]. LIF, after binding to the LIFR/gp130 heterodimer, can trigger three signalling pathways, namely JAK/Stat3, PI3K/Akt and SHP2/MAPK. However, the Stat3 branch of LIF signalling has been demonstrated to play a central role in the regulation of self-renewal and pluripotency of mESCs [3]. In fact, overexpression of a dominant negative variant of Stat3 in mESCs leads to loss of pluripotency and enhanced cell differentiation [4]. Furthermore, Stat3 activation is sufficient to maintain the undifferentiated state of mESCs, as demonstrated in a study using a fusion protein between Stat3 and the ligand binding domain of the estrogen receptor (ER) [5]. Additionally, deletion of Stat3 causes embryonic lethality as Stat32/ 2 embryos have reduced growth of the inner cell mass (ICM) and show rapid degeneration between days E6.5?E7.5 [6]. Thus, CreloxP systems have been used to investigate the role of Stat3 in different cell types. In the small intestine, Stat3 is absolutely required for survival of the stem cells near the base of the crypt [7] and expression of dominant negative Stat3 in hematopoietic stemcells results in a reduced lympho-myeloid reconstituting ability [8]. In the mammary gland Stat3 is activated early during postlactational regression and is a major regulator of the extensive cell death and tissue remodelling that occurs during this process [9,10]. Recently, we demonstrated that activation of Stat3 is required during mammary gland involution to upregulate the expression of the lysosomal proteases, cathepsins B and L, and to downregulate the expression of their endogenous cytoplasmic inhibitor (Spi2A) thereby mediating cell death [11]. However, a potential role for Stat3 in mammary stem cells has not been determined. Mammary epithelium consists of luminal (ductal and alveolar) and basal (myoepithelial) cells that are organised into a bi-layered structure with luminal cells lining the lumen encased by an outer layer of basal cells [12]. It is presumed that both luminal and basal lineages originate from common embryonic stem and progenitor cells. Moreover, each pregnancy cycle is accompanied by the massive expansion of the mammary epithelial compartment which suggests that the adult mammary gland contains a population of stem/progenitor cells with long-term self-renewal potential [13]. Previous reports have confirmed that mammary stem cells transplanted into a cleared fat pad can regenerate a functional mammary epithelial tree [14,15,16,17]. Moreover, each full-term pregnancy cycle generates so called parity-induced mammary epithelial cells (PI-MECs) that produce milk proteins during late gestation and lactation and do not undergo programmed cell death 15826876 during involution. Some of these cells act as alveolar progenitors during subsequent pregnancies and in vivo transplantation experiments proved their multipotency and self renewalStat3 and Mammary Stem CellsFigure 1. Stat3fl/fl;BLG-Cre+ glands show incomplete involution and luminal progenitors have reduced proliferative capacity. (A) RTPCR analysis of Stat3 expression in FACS sorted populations of mammary epithelial cells. MRU: mammary repopulating units. (B, C) H E staining of sections of Stat3fl/fl;BLG-Cre2 and Stat3fl/fl;BLG-Cre+ mammary glands collected at day 5 of the second gestation (B) or four weeks after natural weaning (C).