Postnatal development and the differential expression of presynaptic terminal-associated proteins in the developing retina of the Brazilian opossum, Monodelphis domestica.

In the present study we have characterized the postnatal (PN) development of the retina in the Brazilian opossum, Monodelphis domestica. Monodelphis, a small, pouchless marsupial, undergoes a protracted period of postnatal development. Using bromodeoxyuridine immunohistochemistry, we have investigated postnatal neurogenesis of the retina. In addition, we have examined the differentiation of the retina by using antibodies directed against the presynaptic terminal-associated proteins synaptotagmin, Rab3A, synaptophysin and synaptosomal-associated protein-25 (SNAP-25), and have characterized their spatial and temporal distribution during postnatal development. This study is the first systematic comparison of the developmental expression of multiple presynaptic terminal-associated proteins in relation to retinal neurogenesis and differentiation. At birth (1PN), the Monodelphis retina was relatively undifferentiated morphologically and birthdating analysis revealed mitotically active cells throughout the retina. The 8PN retina was organized into two cellular layers: an outer region of mitotically active neuroepithelial cells and an inner region of postmitotic cells. The inner plexiform layer formed between 5PN and 10PN, and exhibited unique patterns of immunoreactivity with the antibodies used in this analysis. By 25PN the retina was well laminated, and synaptotagmin-, Rab3A-, synaptophysin- and SNAP-25-like immunoreactivities exhibited distinct and specific patterns within the plexiform layers, although they had not yet achieved their mature, adult patterns. These results indicate that each of these proteins exhibits developmentally regulated changes in its cellular localization, and therefore may play important roles during morphogenesis and synaptogenesis of the vertebrate retina.