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Ultrastructural study of the Merkel cell and its expression of met-enkephalin immunoreactivity during fetal and
1Department of Physiology, Chinese University of Hong Kong.
Abstract:
The morphological changes and the expression of met-enkephalin immunoreactivity of Merkel cells during fetal and postnatal development were investigated in touch domes and sinus hair follicles of mice by transmission electron microscopy. In prenatal fetal mice, the Merkel cells were mainly oval in shape and had slightly lobulated nuclei. These fetal Merkel cells (14, 16, 18 d gestation) which were not innervated showed a large number of accumulated dense-core granules in their cytoplasm as compared with the innervated Merkel cells which appeared in adult mice. No Merkel cells could be found in d 10 and d 12 fetuses. Innervation of Merkel cells was found to increase with age. The location of Merkel cells in juvenile, adult and even old mice was very similar, cells being found mainly in the basal layer of the epithelium. Using the electron-microscopic immunogold method, met-enkephalin-like substance was consistently located in the dense-core granule region of both innervated and noninnervated Merkel cells throughout the whole developmental stage. Interestingly, it was also found that the labelling intensity of met-enkephalin immunoreactivity was significantly higher in Merkel cells of younger age groups than in adult and old age groups. None of the nerve terminals associated with Merkel cells were labelled. The present study supports the theory of an epidermal origin of Merkel cells followed by the trophic growth of nerve fibers induced by the peptides.
Insights
Merkel cells, crucial for touch, develop from the epidermis and contain met-enkephalin peptides. Their innervation and peptide levels change significantly during fetal and postnatal development in mice.
Area of Science:
- Developmental biology
- Neuroscience
- Cell biology
Background:
- Merkel cells are specialized sensory receptors in the skin crucial for tactile sensation.
- Their developmental origins and the role of neuropeptides like met-enkephalin are not fully understood.
Purpose of the Study:
- To investigate the morphological changes and met-enkephalin expression in mouse Merkel cells during development.
- To examine the innervation patterns and peptide localization throughout fetal and postnatal stages.
Main Methods:
- Transmission electron microscopy was used to observe Merkel cell morphology.
- Electron microscopic immunogold labeling identified met-enkephalin immunoreactivity.
- Studies were conducted on mice at various gestational and postnatal ages.
Main Results:
- Merkel cells were first observed at 14 days gestation, initially oval and non-innervated with abundant dense-core granules.
- Innervation increased with age, with cells consistently located in the basal epithelium.
- Met-enkephalin was found in dense-core granules of both innervated and non-innervated cells, with higher intensity in younger mice.
Conclusions:
- The findings support an epidermal origin for Merkel cells.
- Met-enkephalin peptides likely play a role in the trophic growth of associated nerve fibers during development.
