European Journal of Neuroscience, Vol. 8, pp. zyxwvutsrq 521-529, 1996 zyxwvut 0 European Neuroscience Association z Ciliary Neurotrophic Factor Constitutively Expressed in the Nervous System of Transgenic Mice Protects Embryonic Dorsal Root Ganglion Neurons from Apoptosis z Emanuela Tolosano, Miguel Angel Cutufia, Emilio Hirsch, Guglielmo Stefanuto, Samuele Voyron’ , Aldo Fasolo’, Lorenzo Silengo and Fiorella Altruda Department of Genetics, Biology and Medical Chemistry, University of Turin, Via Santena Sbis, 10126 Turin, Italy ’Department of Animal Biology, University of Turin, Italy Keywords: CNTF, transgenic mice, apoptosis Abstract Ciliary neurotrophic factor (CNTF) is a potent survival factor for several neuronal populations. It is expressed postnatally by Schwann cells in the peripheral nervous system and by some glial and neuronal cells in the central nervous system. We used the promoter of the neurofilament light chain gene to produce transgenic mice that express CNTF in neurons from the beginning of neuronal differentiation. These transgenic animals may represent a suitable model zyxwvutsr to identify neuronal cell types responsive to CNTF in vivo and to study the mechanism of action of this neurotrophic factor. We show that dorsal root ganglion neurons of transgenic mice expressing CNTF in neurons are protected from apoptosis during embryonic development: 40% of these cells undergo apoptosis between embryonic day 12.5 and postnatal day 5 in transgenic mice whereas 60% do so in control animals. However, protection from apoptosis does not result in an increase in the total number of neurons at the end of development. We discuss our results with regard to CNTF potentialities in vivo and the significance of programmed cell death during development. Introduction zyxwvutsrqp Ciliary neurotrophic factor (CNTF) was originally identified as a target-derived factor supporting the survival of parasympathetic ciliary ganglion neurons (Barbin et al., 1984). The pleiotropic nature of CNTF action has since been widely established. In vitro CNTF acts as a survival-promoting factor for sympathetic (Blottner et al., 1989; Emsberger et al., 1989), sensory (Skaper and Varon, 1986), hippocampal (Ip et al., 1991). retinal (Hoffmann, 1988), spinal (Arakawa et al., 1990) and cortical motor (Magal et al., 1993) neurons. Moreover, CNTF acts as a phenotype-modulating factor on cultured sympathetic neurons (Saadat et al., 1989; Rao et al., 1992) and 0-2A glial precursor cells (Lillien and Raff, 1990). In vivo, CNTF is able to protect motoneurons from naturally occumng and injury-induced cell death (Sendtner et al., 1990; Oppenheim et al., 1991). In addition it can prevent axotomy-induced degeneration of septa1 (Hagg et al., 1992). thalamic (Clatterbuck et al., 1993). retinal (Mey and Thanos, 1993) and substantia nigra (Hagg and Varon, 1993) neurons. CNTF is prevalently expressed by myelinating Schwann cells in the peripheral nervous system (PNS) and by selected glial and neuronal populations in the central nervous system (CNS) (Stockli et al., 1991; Dobrea et al., 1992; Rende et al., 1992; Henderson et al., 1994). The protein has been detected only during postnatal development and in adulthood. During embryonic development a transcript for CNTF is detectable as early as embryonic day (E) 11 in the rat (Ip et al., 1993), but the protein has not been revealed so far. Gene-targeted knockout mice that lack CNTF develop normally, but their motoneurons atrophy 4 weeks after birth, resulting in a significant reduction in muscle strength (Masu et al., 1993). Taken together, these data have suggested that CNTF is not a target-derived neurotrophic factor involved in the establishment of the nervous system, but is important for the postnatal maintenance of some neuronal populations, particularly motoneurons (Davies, 1993). Nevertheless the wide range of neuronal populations responsive in vitro to CNTF, its potency as a neurotrophic factor and the wide distribution of its receptor have led to the suggestion that it may have therapeutic effectiveness in the treatment of several neurological diseases. In this respect it is important to identify which neuronal populations are able to respond to CNTF in vivo and to know how z CNTF exerts its action. The mechanism of action of neurotrophic factors has been investi- gated in vitro; sympathetic neurons of the superior cervical ganglion maintained in culture in the presence of nerve growth factor (NGF) undergo cell death after removing the growth factor (Martin et al., 1988). NGF deprivation-induced death is morphologically apoptotic and is accompanied by DNA cleavage into oligonucleosome-sized fragments. Apoptosis can be prevented by inhibitors of RNA or protein synthesis, indicating that cell death is due to the activation of a specific genetic programme. Similar results have been obtained Correspondence to: zyxwvutsrqpo Fiorella Altruda, as above Received 19 June 1995, revised I September 1995, accepted I0 October 1995