Developmental biology at the Howard Florey Institute.

1. A brief account of the history of developmental biology at the Howard Florey Institute, as well as in a wider general context, is presented and some of the results of developmental studies performed at the Institute over the past 7 years are discussed. 2. In the foetal rat, parathyroid hormone rather than parathyroid hormone-related protein is produced by the parathyroid anlage. This contrasts with results reported by others for the sheep. 3. The control of imprinting of H19 and insulin-like growth factor-II has been studied in the mouse using gene knockout of the coding region of the H19 gene. Bi-allelic expression of H19 in some liver and gut cells was observed. 4. Gene knockout of the homeobox gene Cdx2 produced dramatic effects. Homozygous embryos did not implant in the uterus. Heterozygotes exhibited homeosis involving the gut and skeleton. Animals developed intestinal tumours within a few weeks of birth.