George Cachianes

Cloning, expression during development, and evidence for release of a trophic factor for ciliary ganglion neurons

Ciliary ganglion (CG) neurons undergo a period of cell death during development that may be regulated by the limited availability of trophic factor produced by their target tissues. We have previously reported the purification of a ciliary neurotrophic factor from adult chick sciatic nerve that we called growth promoting activity (GPA). Here we demonstrate that GPA can be purified and cloned from embryonic day 15 (E15) chick eyes, which contain all the target tissues of the CG. Our studies show the following: GPA mRNA is induced in embryonic chick eyes during the period of CG neuron cell death; GPA mRNA is expressed specifically in the layer of the eye that contains the targets of the CG and in primary cultures of smooth muscle cells isolated from the choroid layer of the eye; and biologically active GPA is released from cells transfected with a GPA cDNA.

GROWTH HORMONE RECEPTORS AND BINDING PROTEINS

Growth hormone receptors are found in a wide variety of tissues and are thought to mediate the various actions of growth hormone. Recently, a growth hormone binding protein was demonstrated in serum and shown to have antigenic identity with the liver growth hormone receptor by use of a panel of monoclonal antibodies to the receptor. Here we describe the purification, part sequence and cloning of the rabbit liver growth hormone receptor. Purification and N terminal sequence analysis of the rabbit serum binding protein for GH showed it to be identical to the extracellular region of the rabbit liver GH receptor. Rabbit liver receptor and human binding protein sequences were expressed in COS-7 cells and shown to display predicted hormone specificity and antigenic characteristics. Finally, the rabbit mammary gland prolactin receptor was purified and part sequenced. This showed 34% homology with the rabbit liver GH receptor, and therefore constitutes the second member of a new class of transmembrane receptors regulating growth and lactation.