Single-Cell Transcriptomes Distinguish Stem Cell State Changes and Lineage Specification Programs in Early Mammary Gland Development.

The mammary gland consists of cells with gene expression patterns reflecting their cellular origins, function, and spatiotemporal context. However, knowledge of developmental kinetics and mechanisms of lineage specification is lacking. We address this significant knowledge gap by generating a single-cell transcriptome atlas encompassing embryonic, postnatal, and adult mouse mammary development.

A versatile platform to analyze low-affinity and transient protein-protein interactions in living cells in real time.

Protein-protein interactions (PPIs) play central roles in orchestrating biological processes. While some PPIs are stable, many important ones are transient and hard to detect with conventional approaches. We developed ReBiL, a recombinase enhanced bimolecular luciferase complementation platform, to enable detection of weak PPIs in living cells.

Paracrine Wnt signaling both promotes and inhibits human breast tumor growth.

Wnt signaling in mouse mammary development and tumorigenesis has been heavily studied and characterized, but its role in human breast cancer remains elusive. Although Wnt inhibitors are in early clinical development, it is unclear whether they will be of therapeutic benefit to breast cancer patients, and subsequently, to which ones. To address this, we generated a panel of Wnt reporting human breast cancer cell lines and identified a previously unrecognized enrichment for the ability to respond to Wnt in the basal B or claudin-low subtype, which has a poor prognosis and no available targeted therapies.

BH3 activation blocks Hdmx suppression of apoptosis and cooperates with Nutlin to induce cell death.

The Hdmx protein restricts p53 activity in vivo and is overexpressed in a significant fraction of human tumors that retain the wild type p53 allele. An understanding of how Hdmx limits p53 activation and blocks apoptosis could therefore lead to development of novel therapeutic agents. We previously showed that Hdmx modulates tumor cell sensitivity to Nutlin-3a, a potent antagonist of the p53/Hdm2 interaction.

Quantitative analyses reveal the importance of regulated Hdmx degradation for p53 activation.

P53 regulates numerous downstream targets to induce cell cycle arrest, senescence, apoptosis, and DNA repair in response to diverse stresses. Hdm2 and Hdmx are critical negative regulators of P53 because Hdm2 regulates P53 abundance, and both can antagonize P53 transactivation. Modest changes in Hdm2 or Hdmx abundance affect P53 regulation, yet quantitative information regarding their endogenous intracellular concentrations and subcellular distributions during a stress response are lacking.

Mouse mutants reveal that putative protein interaction sites in the p53 proline-rich domain are dispensable for tumor suppression.

The stability and activity of tumor suppressor p53 are tightly regulated and partially depend on the p53 proline-rich domain (PRD). We recently analyzed mice expressing p53 with a deletion of the PRD (p53(DeltaP)). p53(DeltaP), a weak transactivator hypersensitive to Mdm2-mediated degradation, is unable to suppress oncogene-induced tumors.

A mouse p53 mutant lacking the proline-rich domain rescues Mdm4 deficiency and provides insight into the Mdm2-Mdm4-p53 regulatory network.

The mechanisms by which Mdm2 and Mdm4 (MdmX) regulate p53 remain controversial. We generated a mouse encoding p53 lacking the proline-rich domain (p53DeltaP). p53DeltaP exhibited increased sensitivity to Mdm2-dependent degradation and decreased transactivation capacity, correlating with deficient cell cycle arrest and reduced apoptotic responses.

Replication initiation patterns in the beta-globin loci of totipotent and differentiated murine cells: evidence for multiple initiation regions.

The replication initiation pattern of the murine beta-globin locus was analyzed in totipotent embryonic stem cells and in differentiated cell lines. Initiation events in the murine beta-globin locus were detected in a region extending from the embryonic Ey gene to the adult betaminor gene, unlike the restricted initiation observed in the human locus. Totipotent and differentiated cells exhibited similar initiation patterns.