Notch-Wnt signal crosstalk regulates proliferation and differentiation of osteoprogenitor cells during intramembranous bone healing.

Adult bone regeneration is orchestrated by the precise actions of osteoprogenitor cells (OPCs). However, the mechanisms by which OPC proliferation and differentiation are linked and thereby regulated are yet to be defined. Here, we present evidence that during intramembranous bone formation OPC proliferation is controlled by Notch signaling, while differentiation is initiated by activation of canonical Wnt signaling. The temporospatial separation of Notch and Wnt signal activation during the early stages of bone regeneration suggests crosstalk between the two pathways. In vitro and in vivo manipulation of the two essential pathways demonstrate that Wnt activation leads to initiation of osteogenic differentiation and at the same time inhibits Notch signaling, which results in termination of the proliferative phase. Here, we establish canonical Wnt signaling as a key regulator that facilitates the crosstalk between OPC proliferation and differentiation during intramembranous, primary bone healing.

A brief overview of the development of aerospace medicine in the United States.

Aerospace medicine has evolved into a legitimate specialty through a long process of historical observation and technical achievement. However, most public literature on the topic has only covered information written through the late 1960s. This paper seeks to give a brief overview of the development of aerospace medicine and includes information about early advances in the field as well as more recent data. A MEDLINE search using "history," "aerospace medicine," and several other search terms as subject headings was the first step in gathering data. Also, personnel from the U.S. Air Force School of Aerospace Medicine library at Brooks AFB, TX, were consulted for current literature on the subject. From the earliest descriptions of mountain sickness, to the first manned balloon flight, and on to the invention of the airplane with man's forays into space, aerospace medicine has had a rich history. A great part of this rich history was contributed by pioneers, both past and present, of the U.S. Air Force.