Project description:Circadian rhythms play key roles in daily physiological functions, development, and cancer. Period 2 (PER2) is a repressive element which inhibits transcription activated by positive clock elements resulting in diurnal cycling of genes. Here we show, that outside of time keeping, PER2 has a non-circadian function that is critical to mammary gland development. Virgin Per2 deficient mice, Per2ldc, have underdeveloped glands containing fewer bifurcations and terminal ducts. Using a transplantation model, we show that these changes are intrinsic to the gland and furthermore identify changes in cell fate commitment. Per2ldc mouse mammary glands have a luminal/basal bi-potent phenotype in cells of the ductal epithelium. We identified co-localization of E-cadherin and Keratin 14 in luminal cells and decreased p63 staining and gene expression in myoepithelial cells. Moreover, Per2ldc mice overexpress SLUG, which is related to mammary stem cell maintenance and EMT. Similar results were demonstrated using MCF10A and shPER2 MCF10A cell lines. Collectively this study reveals a critical non-circadian function of PER2 in mammary gland development, validates the Per2ldc model, and describes a potential role for PER2 in breast cancer.
Project description:Branching morphogenesis of the mammary gland is driven by the highly motile terminal end bud (TEB) throughout pubertal development. The stem cell enriched, proliferative TEB branches as it invades the mammary fat pad to create a complex network of ducts. The gene expression programs specific to the TEB and the differentiated duct are poorly understood. We conducted a time course analysis of gene expression in the TEB and duct throughout branching morphogenesis. Additionally, we determined the gene regulatory networks coordinated by the Co-factor of LIM domains (CLIM/LDB) transcriptional regulators and determined an essential function for CLIMs in branching morphogenesis by maintaining basal mammary epithelial stem cells and promoting cell proliferation. We used laser capture microdissection to isolate TEB and duct cells throughout branching morphogenesis. We then profiled gene expression in these cells to determine gene regulatory networks involved in branching morphogenesis, and specifically those regulated by CLIM transcriptional regulators. Mouse mammary glands from 4, 6, 8, and 10 week old mice (early puberty through early adulthood) were used for laser capture microdissection of TEB and duct cells from WT and K14-DN-Clim transgenic mice. RNA was isolated (Qiagen) and hybridized to Affymetrix MouseGene 1.0 ST arrays. In addition, basal (CD29HiCD24+Lin-) and Luminal (CD29LoCD24+Lin-) cells were sorted and RNA collected for hybridization to Affymetrix MouseGene 1.0ST arrays.
Project description:Branching morphogenesis of the mammary gland is driven by the highly motile terminal end bud (TEB) throughout pubertal development. The stem cell enriched, proliferative TEB branches as it invades the mammary fat pad to create a complex network of ducts. The gene expression programs specific to the TEB and the differentiated duct are poorly understood. We conducted a time course analysis of gene expression in the TEB and duct throughout branching morphogenesis. Additionally, we determined the gene regulatory networks coordinated by the Co-factor of LIM domains (CLIM/LDB) transcriptional regulators and determined an essential function for CLIMs in branching morphogenesis by maintaining basal mammary epithelial stem cells and promoting cell proliferation. We used laser capture microdissection to isolate TEB and duct cells throughout branching morphogenesis. We then profiled gene expression in these cells to determine gene regulatory networks involved in branching morphogenesis, and specifically those regulated by CLIM transcriptional regulators.
Project description:During mammary gland development, an epithelial bud undergoes branching morphogenesis to expand into a continuous tree-like network of branched ducts [1]. The process involves multiple cell types that are coordinated by hormones and growth factors coupled with signaling events including Wnt and Hedgehog [2-5]. Primary cilia play key roles in the development of many organs by coordinating extracellular signaling (of Wnt and Hedgehog) with cellular physiology [6-8]. During mammary development, we find cilia on luminal epithelial, myoepithelial, and stromal cells during early branching morphogenesis when epithelial ducts extend into the fat pad and undergo branching morphogenesis. When branching is complete, cilia disappear from luminal epithelial cells but remain on myoepithelial and stromal cells. Ciliary dysfunction caused by intraflagellar transport defects results in branching defects. These include decreased ductal extension and decreased secondary and tertiary branching, along with reduced lobular-alveolar development during pregnancy and lactation. We find increased canonical Wnt and decreased Hedgehog signaling in the mutant glands, which is consistent with the role of cilia in regulating these pathways [6-11]. In mammary gland and other organs, increased canonical Wnt [12-14] and decreased Hedgehog [15, 16] signaling decrease branching morphogenesis, suggesting that Wnt and Hedgehog signaling connect ciliary dysfunction to branching defects.
Project description:Branching morphogenesis is essential for the successful development of a functional lung to accomplish its gas exchange function. Although many studies have highlighted requirements for the bone morphogenetic protein (BMP) signaling pathway during branching morphogenesis, little is known about how BMP signalingis regulated. Here we report that the protein arginine methyltransferase 5 (Prmt5) and symmetric dimethylation at histone H4 arginine 3 (H4R3sme2) directly associate with chromatin of Bmp4 to suppress its transcription. Inactivation of Prmt5 in the lung epithelium results in halted branching morphogenesis, altered epithelial cell differentiation and neonatal lethality. These defects are accompanied by increased apoptosis and reduced proliferation of lung epithelium, as a consequence of elevated canonical BMP-Smad1/5/9 signaling. Inhibition of BMP signaling by Noggin rescues the lung branching defects of Prmt5 mutant in vitro. Taken together, our results identify a novel mechanism through which Prmt5-mediated histone arginine methylation represses canonical BMP signaling to regulate lung branching morphogenesis.
Project description:Although the neuropilins were characterized as semaphorin receptors that regulate axon guidance, they also function as vascular endothelial growth factor (VEGF) receptors and contribute to the development of other tissues. Here, we assessed the role of NRP2 in mouse mammary gland development based on our observation that NRP2 is expressed preferentially in the terminal end buds of developing glands. A floxed NRP2 mouse was bred with an MMTV-Cre strain to generate a mammary gland-specific knockout of NRP2. MMTV-Cre;NRP2(loxP/loxP) mice exhibited significant defects in branching morphogenesis and ductal outgrowth compared with either littermate MMTV-Cre;NRP2(+/loxP) or MMTV-Cre mice. Mechanistic insight into this morphological defect was obtained from a mouse mammary cell line in which we observed that VEGF(165), an NRP2 ligand, induces branching morphogenesis in 3D cultures and that branching is dependent upon NRP2 as shown using shRNAs and a function-blocking antibody. Epithelial cells in the mouse mammary gland express VEGF, supporting the hypothesis that this NRP2 ligand contributes to mammary gland morphogenesis. Importantly, we demonstrate that VEGF and NRP2 activate focal adhesion kinase (FAK) and promote FAK-dependent branching morphogenesis in vitro. The significance of this mechanism is substantiated by our finding that FAK activation is diminished significantly in developing MMTV-Cre;NRP2(loxP/loxP) mammary glands compared with control glands. Together, our data reveal a VEGF/NRP2/FAK signaling axis that is important for branching morphogenesis and mammary gland development. In a broader context, our data support an emerging hypothesis that directional outgrowth and branching morphogenesis in a variety of tissues are influenced by signals that were identified initially for their role in axon guidance.
Project description:Progesterone (P4)-activated progesterone receptors (PRs) play an essential role in driving pregnancy-associated mammary ductal side-branching morphogenesis and alveologenesis. However, the global cistromic and transcriptome responses that are required to elicit P4-dependent branching morphogenesis have not been elucidated. By combining chromatin immunoprecipitation followed by deep sequencing to identify genome-wide PR-binding sites in PR-positive luminal epithelial cells with global gene expression signatures acutely regulated by PRs in the mammary gland, we have identified a mammary epithelial PR targetome associated with active P4-dependent branching morphogenesis in vivo. We demonstrate that P4-induced side-branching is initiated by epithelial cell rearrangement into a multilayered epithelium that sprouts laterally from quiescent ducts via a mechanism requiring P4-dependent activation of Rac-GTPase signaling. We identify effectors of Rac-GTPases as direct transcriptional targets of PRs, and we demonstrate that disruption of the P4-activated Rac-GTPase signaling axis is sufficient to eliminate P4-dependent side-branching. Our data reveal that the molecular mediators of P4-dependent ductal side-branching overlap with those implicated in breast cancer.
Project description:Mechanical forces are increasingly recognized to regulate morphogenesis, but how this is accomplished in the context of the multiple tissues present within a developing organ remains unclear. Here we use bioengineered “microfluidic chest cavities” to precisely control the mechanical environment of the fetal lung. We show that transmural pressure controls airway branching morphogenesis and regulates the frequency of airway smooth muscle contraction. Next-generation sequencing analysis shows that lungs held at higher pressure are more mature than lungs held at lower pressure. Timelapse imaging reveals that branching events are synchronized across distant locations within the lung, and are preceded by long-duration waves of airway smooth muscle contraction. Higher transmural pressure decreases the interval between systemic smooth muscle contractions and increases the rate of morphogenesis of the airway epithelium. These data reveal that the mechanical properties of the microenvironment instruct crosstalk between tissues to control the rate of development of the embryonic lung.
Project description:The Ron receptor tyrosine kinase is expressed in normal breast tissue and is overexpressed in approximately 50% of human breast cancers. Despite the recent studies on Ron in breast cancer, nothing is known about the importance of this protein during breast development. To investigate the functional significance of Ron in the normal mammary gland, we compared mammary gland development in wild-type mice to mice containing a targeted ablation of the tyrosine kinase (TK) signaling domain of Ron (TK-/-). Mammary glands from RonTK-/- mice exhibited accelerated pubertal development including significantly increased ductal extension and branching morphogenesis. While circulating levels of estrogen, progesterone, and overall rates of epithelial cell turnover were unchanged, significant increases in phosphorylated MAPK, which predominantly localized to the epithelium, were associated with increased branching morphogenesis. Additionally, purified RonTK-/- epithelial cells cultured ex vivo exhibited enhanced branching morphogenesis, which was reduced upon MAPK inhibition. Microarray analysis of pubertal RonTK-/- glands revealed 393 genes temporally impacted by Ron expression with significant changes observed in signaling networks regulating development, morphogenesis, differentiation, cell motility, and adhesion. In total, these studies represent the first evidence of a role for the Ron receptor tyrosine kinase as a critical negative regulator of mammary development.