Mice that have been specially bred to lack a protein known as Grf-1, which is normally found only in the brain, do not grow properly after they are born and remain small all their lives. We have now identified a function of Grf-1 as an important regulator of the synthesis and release of growth hormone. Moreover, grf1, the gene encoding this protein, is unlike other imprinted genes that affect growth because it operates after, rather than before, birth.

1. Rhône-Poulenc Rorer, Centre de Recherche de Vitry-Alfortville, Vitry-sur-Seine, France
2. Present address: BioScreen Therapeutics, 58 Bd St Denis, 92400 Courbevoie, France
3. Biodynamique des Systémes Neuroendocriniens, INSERM U-159, Centre Paul Broca, Paris, France
4. Unité de Recherches sur les Handicaps Génétiques de l Enfant, INSERM U-393, Hpital des Enfants-Malades, Paris, France
5. Génétique Moléculaire et Intégration des Fonctions Cellulaires, CNRS UPR 9044, Institut de Recherches sur le Cancer, Villejuif, France