The development of alkaline phosphatase activity in limb buds of mouse embryos in vitro and its relation to chondrogenesis

The development of alkaline phosphatase (aPh) activity and chondrogenesis were studied in the limb buds of mouse embryos (day 11 p.c.) that had been grown in an organ culture. During a 12-day culture period an increase in aPh activity to more than 40 mU/limb bud was measured from day 2 in vitro onward. Depending on the time of application, aPh formation can be inhibited by certain substances. Cytosine-arabinoside inhibits aPh activity when the substance is added on day 2, 3, or 4. Chondrogenesis, on the other hand, is affected on days 1, 2, and 3 and to a lesser degree on day 4. Actinomycin D interferes with aPh activity after its addition on day 1, 2, 3, or 4. Chondrogenesis is only inhibited when the drug is applied on the 1st, 2nd, or to a lesser degree on the 3rd day. Cycloheximide inhibits aPh formation on all days of treatment, but to a lesser degree on days 5 and 6; chondrogenesis is most influenced on days 2, 3, and 4. On day 6 of the culture period, aPh activity can be demonstrated histochemically only in the region of humerus and proximal parts of radius and ulna. Alterations in the distal cartilage skeleton, therefore, do not influence the activity data. A prerequisite for an increase in aPh activity is cartilage growth in the proximal part of the limb buds and subsequent induction of a perichondral cell population to proliferation and differentiation.