| Abstrakt: |
To clarify whether the common α-subunit of glycoprotein hormones is involved in photic signal transduction, α-subunit mRNA levels in the pars tuberalis (PT) of both hamsters and chickens were estimated at different time points of the day/night cycle by laser capture microdissection (LCM) and real-time quantitative polymerase chain reaction (PCR). Distinct diurnal rhythms were found for α-subunit mRNA expression in both species. In the hamster PT, α-subunit mRNA levels gradually increased during the dark phase; the diurnal peak was found at time (ZT) 21. The lowest value was obtained at ZT 5 during the day. In the chicken PT, α-subunit mRNA levels were maintained at a low constant level at night between ZT 13 and 21. Thus, α-subunit mRNA expression in the PT depends on the light–dark cycle and may be controlled by the pineal hormone melatonin. The effect of various photoperiods on the hamster PT was examined by real-time PCR, immunohistochemistry, and electron microscopy. In hamsters kept under short photoperiod (L/D=8 h:16 h) or complete darkness, a dramatic decrease of α-subunit mRNA level was induced, and the PT-specific cells accumulated glycogen-like particles and enlarged secretory granules. Under long photoperiods (L/D=16 h:8 h), however, the α-subunit mRNA level was elevated and the PT-specific cells exhibited highly active features, i.e., piles of lamellar cisternae of rough endoplasmic reticulum and well-developed Golgi complexes. The α-subunit synthesized by the PT-specific cells may therefore participate in the circadian and seasonal regulation of endocrine activities. [ABSTRACT FROM AUTHOR] |
Full text from SpringerLink