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Microfilaments, the smooth endoplasmic reticulum and synaptic ribbon fields in the pinealocytes of the baboon (Papio
Abstract:
Microfilaments (MF, 5-8 nm in diameter) are a prominent feature of the pinealocyte cytoplasm of baboons (Papio ursinus) kept under controlled lighting conditions. MF occurred as a filamentous network in these cells during the light phase of the diurnal light-dark cycle, while a close structural association was noted between MF and the membranes of the smooth endoplasmic reticulum (SER). This association was especially evident during the dark period. Increased numbers of single synaptic ribbons (SR, vesicle-crowned rodlets), together with large aggregations of SR, i.e., ribbon fields (RF), were seen in the pinealocyte cytoplasm of baboons killed during the dark phase. It is suggested that the vesicles of RF may arise from those of the SER and that MF may play a role in the movement of SER-vesicles to those areas of the cytoplasm where new RF are being formed.
Insights
Microfilaments (MF) form networks in baboon pinealocytes, associating with smooth endoplasmic reticulum (SER) membranes. This suggests MF may transport SER vesicles for forming synaptic ribbon aggregations during darkness.
Area of Science:
- Cell Biology
- Neuroendocrinology
Background:
- Pinealocytes are key cells in the pineal gland, regulating circadian rhythms.
- The cytoskeleton, including microfilaments (MF), plays crucial roles in cellular structure and function.
- The smooth endoplasmic reticulum (SER) is involved in lipid synthesis and calcium storage.
Purpose of the Study:
- To investigate the structural associations of microfilaments (MF) with smooth endoplasmic reticulum (SER) in baboon pinealocytes.
- To examine the changes in MF and synaptic ribbon (SR) structures during different phases of the diurnal light-dark cycle.
- To elucidate the potential role of MF in the formation of synaptic ribbons (SR) and ribbon fields (RF).
Main Methods:
- Transmission electron microscopy was used to examine baboon (Papio ursinus) pinealocyte ultrastructure.
- Pinealocytes were collected from animals maintained under controlled lighting conditions (light and dark phases).
- Morphometric analysis was performed to quantify microfilaments, smooth endoplasmic reticulum, and synaptic ribbon structures.
Main Results:
- Microfilaments (MF) formed a filamentous network within baboon pinealocyte cytoplasm during the light phase.
- A close structural association between MF and smooth endoplasmic reticulum (SER) membranes was observed, particularly during the dark phase.
- Increased numbers of single synaptic ribbons (SR) and large aggregations (ribbon fields, RF) were noted in pinealocytes during the dark phase.
Conclusions:
- The structural association between MF and SER suggests a functional relationship.
- It is proposed that SER vesicles contribute to the formation of synaptic ribbons (SR) and ribbon fields (RF).
- Microfilaments (MF) may facilitate the transport of SER-derived vesicles for the assembly of ribbon fields in pinealocytes during the dark period.