Molecular cloning, expression and regional distribution of rat ciliary neurotrophic factor

Abstract

CILIARY neurotrophic factor (CNTF) was originally characterized as a survival factor for chick ciliary neurons in vitro¹. More recently, it was shown to promote the survival of a variety of other neuronal cell types^2,3 and to affect the differentiation of E7 chick sympathetic neurons by inhibiting their proliferation and by inducing the expression of vasoactive intestinal peptide immunoreac-tivity (VIP-IR) ⁴. In cultures of dissociated sympathetic neurons from newborn rats, CNTF induces cholinergic differentiation as shown by increased levels of choline acetyltransferase (ChAT) ⁵. This increase is paralleled by a reduction of tyrosine hydroxylase (TH) activity. Moreover, CNTF promotes the differentiation of bipotential 02A progenitor cells to type-2-astrocytes⁶ in vitro. To help establish which, if any, of these functions CNTF exerts in vivo, it is necessary to determine its primary structure, cellular expression, developmental regulation and localization. The complementary DNA-deduced amino-acid sequence and subsequent expression of cDNA clones covering the entire coding region in HeLa-cells indicate that CNTF is a cytosolic protein. This, together with its regional distribution and its developmental expression, show that CNTF is not a target-derived neurotrophic factor. CNTF thus seems to exhibit neurotrophic and differentiation properties only after becoming available either by cellular lesion or by an unknown release mechanism.