Mark C. Horowitz

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In mammalian skin, multiple types of resident cells are required to create a functional tissue and support tissue homeostasis and regeneration. The cells that compose the epithelial stem cell niche for skin homeostasis and regeneration are not well defined. Here, we identify adipose precursor cells within the skin and demonstrate that their dynamic(More)
Interleukin-6 (IL-6) is an important mediator of parathyroid hormone (PTH)-induced bone resorption. Serum levels of IL-6 and its soluble receptor (IL-6sR) are regulated in part by PTH. The PTH/PTH-related protein type 1 receptor is highly expressed in the liver, and in the current study we investigated whether the liver produces IL-6 or IL-6sR in response(More)
Osteoblasts are the cells responsible for the secretion of collagen and ultimately the formation of new bone. These cells have also been shown to regulate osteoclast activity by the secretion of cytokines, which remain to be defined. In an attempt to identify these unknown cytokines, we have induced primary murine osteoblasts with two bone active agents,(More)
Pax5 encodes BSAP, a member of the paired box domain transcription factors, whose expression is restricted to B lymphocyte lineage cells. Pax5(-/-) mice have a developmental arrest of the B cell lineage at the pro-B cell stage. We show here that Pax5(-/-) mice are severely osteopenic, missing 60% of their bone mass. The osteopenia can be accounted for by a(More)
Marrow adipose tissue (MAT) is a unique fat depot, located in the skeleton, that has the potential to contribute to both local and systemic metabolic processes. In this review we highlight several recent conceptual developments pertaining to the origin and function of MAT adipocytes; consider the relationship of MAT to beige, brown, and white adipose(More)
The formation of brown, white, and beige adipocytes has been a subject of intense scientific interest in recent years due to the growing obesity epidemic in the USA and around the world. This interest has led to the identification and characterization of specific tissue-resident progenitor cells that give rise to each adipocyte population in vivo. However,(More)
Presently there is no clear evidence for the ability of mature osteogenic lineage cells to dedifferentiate. In order to identify and trace mature osteogenic lineage cells, we have utilized transgenic mouse models in which the dentin matrix protein 1 (Dmp1) promoter drives expression of GFP (active marker) or Cre recombinase (historic label) in(More)
The coordination of multiple cytokines and transcription factors with their downstream signaling pathways has been shown to be integral to nephron maturation. Here we present a completely novel role for the helix-loop-helix transcription factor Early B-cell factor 1 (Ebf1), originally identified for B-cell maturation, for the proper maturation of glomerular(More)