RT Journal Article SR Electronic T1 The acquisition of target dependence by developing rat retinal ganglion cells JF eneuro JO eneuro FD Society for Neuroscience SP ENEURO.0044-14.2015 DO 10.1523/ENEURO.0044-14.2015 A1 Colette Moses A1 Lachlan PG Wheeler A1 Chrisna J LeVaillant A1 Anne Kramer A1 Marisa Ryan A1 Greg S Cozens A1 Anil Sharma A1 Margaret A Pollett A1 Jennifer Rodger A1 Alan R Harvey YR 2015 UL http://www.eneuro.org/content/early/2015/06/28/ENEURO.0044-14.2015.abstract AB Similar to neurons in the peripheral nervous system, immature CNS-derived retinal ganglion cells (RGCs) become dependent on target-derived neurotrophic support as their axons reach termination sites in the brain. To study the factors that influence this developmental transition we took advantage of the fact that rat RGCs are born, and target innervation occurs, over a protracted period of time. Early-born RGCs have axons in the superior colliculus (SC) by birth (P0) whereas axons from late-born RGCs do not innervate the SC until P4-P5. Birth dating RGCs using EdU allowed us to identify RGCs (i) with axons still growing towards targets, (ii) transitioning to target dependence, and (iii) entirely dependent on target-derived support. Using laser capture microdissection we isolated about 34,000 EdU+ RGCs and analyzed transcript expression by custom qPCR array. Statistical analyses revealed a difference in gene expression profiles in actively growing RGCs compared to target dependent RGCs, as well as in transitional versus target dependent RGCs. Prior to innervation RGCs expressed high levels of brain-derived neurotrophic factor (BDNF) and ciliary neurotrophic factor receptor alpha but lower levels of neurexin 1 mRNA. Analysis also revealed greater expression of transcripts for signalling molecules such as MAPK, Akt, CREB and STAT. In a supporting in vitro study, purified birth-dated P1 RGCs were cultured for 24-48 hours with or without BDNF; lack of BDNF resulted in significant loss of early- but not late-born RGCs. In summary, we identified several important changes in RGC signalling that may form the basis for the switch from target independence to dependence.Significance Statement: During brain development many neurons die around the time that neural connections are established. This cell loss is thought to be due to competition between neurons for limited amounts of target-derived trophic support; responsive neurons receiving sufficient amounts of such factors survive. But what factors sustain developing neurons prior to target innervation? We took advantage of the fact that rat retinal ganglion cells (RGCs) are born, and target innervation occurs, over a protracted time period. Using laser-capture microdissection of birth-dated RGCs we compared gene expression in neurons prior to, during, and after innervation of central targets. We identified numerous changes in RGC signalling that may form the basis for the switch from target independence to dependence, from axonal elongation to arborization/synaptogenesis.