Perinatal development of melanopsin expression in the mouse retina

📖 Top 20% JournalSep 20, 2011Brain research

Development of light-sensitive cells in the mouse eye around birth

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Circadian Biology on OpenScience ↗PubMed ↗DOI ↗

Abstract

Melanopsin expression in retinal ganglion cells increased significantly around birth, with a notable rise from embryonic day 19 to postnatal day 0.

Melanopsin-expressing cells were identified in mice as early as embryonic day 15.
No change in the number of these cells was observed between embryonic days 16 and 19.
A significant increase in melanopsin expression occurred just before and on the day of birth.
This increase was evident even in samples collected during the night after birth, indicating it was not induced by light exposure.
Analysis of retinas under constant light or darkness showed no differences in melanopsin-expressing cell numbers, suggesting ambient light conditions did not affect the increase.
The rise in melanopsin expression may be associated with maternal or developmental signals related to early retinal connections.

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The melanopsin-expressing retinal ganglion cells are specialized in measuring irradiance for several functions, including daily photoentrainment and regulation of pupil size. In the present study, these cells were analyzed in mice during their perinatal period, from embryonic day (E) 15 to postnatal day (P) 1. Melanopsin expression was detected at E15 in cells that did not co-express the transcription factor Brn3a. Under light/dark (LD) cycles, the number of melanopsin-expressing cells did not change between E16 and E19, while a very significant increase was observed during the short interval around birth, between E19 (the day before birth) and P0 (the day of birth). As these samples were collected after lights on, to determine whether such increase in melanopsin expression was driven by light, we also analyzed samples collected 0-4 hours after birth (during the night period), which revealed that the cell number increase was already present and, therefore, was not induced by the early post-birth light exposure. To clarify the role of ambient light conditions during this period, P1 retinas from pups under constant light or darkness conditions were also analyzed and compared to those of mice under LD cycles. No variation in the number of immunostained cells was detected among the groups studied, indicating that ambient conditions did not provoke the increase in melanopsin expression detected. Rather, it might have been induced by either a maternal or a developmental signal and is likely related to the first connections between the retina and the suprachiasmatic nucleus reported by other authors.

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