Ontogeny of preproenkephalin mRNA expression in the rat retina

Abstract

A b s t r a c t Endogenous opioid systems (i.e. opioid peptides and opioid receptors) modulate developmental events in the neonatal mammalian retina. In the present study, the mRNA encoding preproenkephalin A (PPE), the prohormone for the opioid growth factor (OGF), [Met 5 ]-enkephalin, was studied in the developing and the adult retinas of rats. Northern analysis indicated the presence of a 1.4-kb message in the developing and adult retinas corresponding to rat PPE mRNA. Quantitation showed that PPE message was present on postnatal day 1 at 5% of the adult level, and increased during development until the adult quantity was reached by postnatal day 27. In situ hybridization experiments first detected the presence of PPE mRNA in retinal tissues during late gestation. In late prenatal and neonatal retinas, PPE message was associated with areas of the developing retina containing proliferating neuroblasts and postmitotic cells. Later in development, message appeared to be located primarily within the inner retina, with abundant PPE mRNA associated with putative horizontal cells of the inner nuclear layer (INL). The adult retina showed a similar pattern of PPE gene expression in the cells of the INL. These findings document that the gene expression in the retina for PPE begins in the fetus, continues during retinal development, and coincides with the presence of a PPE mRNA derivative ([Met 5 ]-enkephalin) that regulates DNA synthesis during retinal ontogeny. Our results are also the first to show the presence of PPE message in the adult mammalian retina, suggesting transcription of an opioid gene in the mature visual system. K e y w o r d s : Preproenkephalin A, Retina, Ontogeny, Northern analysis, In situ hybridization, Rat I n t r o d u c t i o n The development of the vertebrate retina has been well docu mented (Braekevelt & Hollenberg, 1970; Griin, 1982; Prada et al., 1991). The various neurons and glia comprising the ret ina arise from a homogeneous matrix of replicating neuroblasts (Sidman, 1961; Meller, 1984). Termination of the proliferation of precursor cells and the initiation of differentiation into adult phenotypes is carefully orchestrated during development, with each cell type leaving the cell cycle in a specific temporal se quence (Sidman, 1961;Meller, 1984; Polleyetal., 1989; Spence & Robson, 1989). The various steps associated with retinal devel opment, such as cell replication, migration, differentiation, are governed by specific growth factors (for review, see Tripathi et al., 1991). Although growth factors associated with the visual system have been studied extensively (Bugra et al., 1993; de la Rosa et al., 1994; Koide et al., 1995; Rickman & Brecha, 1995), the precise identities of the substances which influence retinal development, and the exact phases which they regulate, remain undetermined.

Spatial and Temporal Distribution Patterns of Enkephalinergic Neurons in Adult and Developing Retinas of the Preproenkephalin-Green Fluorescent Protein Transgenic Mouse

“…This report is the first analysis to systematically examine the expression pattern of ENKergic neurons during mouse retinal development. reached by P27 [Isayama et al, 1996]. We suspect that the difference might be related to the different species and research methods.…”

“…Therefore, to better understand the role of ENK in the retina, it is necessary to know the evolution of the population of ENKergic neurons during the course of development. However, the ontogeny of the ENKergic system has only been described in the retina of the rat and chicken by using in situ hybridization histochemistry [Molnar et al, 1995;Isayama et al, 1996;Yang et al, 1997]. The gene expression profile of ENKergic neurons in the developing mouse retina has not been revealed yet.…”

Opioid gene expression in the developing and adult rat heart

“…In situ hybridization experiments were performed according to the methods of Zagon and colleagues (1994;Isayama et al, 1996). Animals of embryonic (E) days 14, 15, 16, 18, and 20 (ϭ E14, E15, E16, E18, and E20), as well as postnatal (P) days 0 (newborn), P5, P10, P21, and P75 (adult) were anesthetized, decapitated, and tissues isolated and frozen in isopentane cooled with dry ice.…”