Abstract
Purpose:
To investigate Neuroglobin (Ngb) mRNA levels, protein expression and distribution during retinal development. Neuroglobin is a neuronal globin that was discovered in 2000. It is found at the highest concentration in the retina and it is believed to be protective in hypoxic-ischaemic injury and in stroke. Ngb may play an important role in O2 storage / transport, detoxification of reactive oxygen species, and/or protection against apoptosis.
Methods:
We used real-time PCR to examine Ngb mRNA levels, Western Blot and immunohistochemistry to examine protein levels and distribution in the retina from wild type C57 BL6 mice from embryonic through to postnatal development stages.
Results:
In the developing mouse retina there was a 21-fold increase in Ngb mRNA level from embryonic day 15 (E15) to postnatal day 30 (P30). There was a 44% increase in Ngb mRNA level between E18 and E 20, and a 34% increase between P7 and P14. Western Blot showed a 2.4-fold increase in Ngb protein from E17 to P2, rising to 2.8-fold peak expression at P6 (compared to E17), followed by a 37% reduction in Ngb protein concentration from P6 to P30. Immunohistochemistry showed that during embryonic / early retinal development (E18-P2), Ngb protein is expressed diffusely throughout the retina with a high concentration in the inner retina, particularly in the ganglion cells. At P14 Ngb protein expression is most pronounced in the photoreceptor inner segments, the inner and outer plexiform layers and in the ganglion cells and this pattern intensifies through to P30.
Conclusions:
Ngb is found in retinal regions which have the highest levels of oxygen consumption and are rich in mitochondria. The retina undergoes very rapid developmental change pre and post-natally and there is a dramatic change in the oxygen environment at birth. Spikes in mRNA levels just before birth and at P7, and spikes in protein expression at birth and P6 followed by a reduction in Ngb protein levels to P30, suggest that Ngb plays a critical role in retinal development and apoptosis.
Keywords: 698 retinal development •
426 apoptosis/cell death •
635 oxygen