The Study of the Ultrastructural and Physiological Functions of Corpora Lutea during the Estrous Cycle in Cattle and Goats
Date Issued
2014
Date
2014
Author(s)
Jiang, Yi-Fan
Abstract
Corpora lutea (CLs) are transient progesterone(P4)-secreting glands necessary for reproduction. In present studies, we investigated the cellular events during the lifespan of CLs in ruminants from the views of morphology, gene expressions and P4 secretion. The histological observation of bovine CLs revealed abundant erythrocytes in the early stage, dense luteal cells without intercellular space in the middle, and the reduction in percentage of luteal cells in the late. The gene expression and P4 level in CLs confirmed the maximum cell number and steroidogenic abilities in the middle CLs, indicating that cell proliferation could be significant during luteal formation.
With growing tissue often under the stress of hypoxia, we tested the expressions of hypoxia inducible factor 1 (HIF1), proliferating cell nuclear antigen (PCNA) and vascular endothelial growth factor A (VEGFA) during estrous cycles in bovine CLs. The genes were highly expressed in the early stage, suggesting that proliferation, hypoxia and angiogenesis could contribute to the formation and function of bovine CLs. Further, we stimulated primary luteal cells from middle CLs and luteinized granulosa cells under hypoxia, to mimic the developing CL in middle and early stages, respectively. The hypoxia inhibited steroidogenesis in both cells, but stimulated cell proliferation and angiogenesis in luteinized granulosa cells. These results suggested that hypoxia could be a critical factor in luteal developments and that cellular response could vary from stage to stage.
For the details, the ultrastructure of goat CLs in various stages was observed. Our analyses revealed proper patterned capillaries in middle CLs, while shrunken luteal cells, expanding regression areas and immune cells with lobed nuclei were identified in the late. Those shrunken cells showed the figures of both autophagy and apoptosis, indicating that programmed cell death might involve CL regression. The active endothelial cells suggested activated angiogenesis in early CLs. On the other hand, the stabilized capillaries and the accumulation of extracellular matrix (ECM) fibers indicated the absence of angiogenesis in the late.
The large luteal cell (LLC) is one of the P4-secreting cells in goat CL. Under transmission electron microscope (TEM), LLCs assembled to form microvillar channels on their surface. With globular structures discerned in the channels, the selective uptake pathway for cholesterol utilization could be significant in goat LLCs. In the cytoplasm, secretion granules and the mitochondria-associated membrane (MAM) were recognized throughout the cycles, while some swollen cisternal ERs were identified only in the early and middle stages. The mitochondria with tubular cristae increased in early and middle LLCs. However, the mitochondria swelled and the cristae shifted to lamellar type in the late, suggesting that plasticity of organelles could contribute to steroidogenesis in goat CLs.
To make the connection between ultrastructure and steriodogenesis, we observed the ultrastructure of a caprine luteal cell line, CLC-D. Preliminary results indicated the morphological shift of mitochondria from lamellar to tubular cristae after steroidogenic treatment. Yet more connections remain to be identified.
In conclusion, our results suggested the cell proliferation and angiogenesis in early CLs, the steroidogenesis in the middle, and the programmed cell death in the late. Luteal cellular responses and ultrastructure vary depending on stages. However, their connections with function, structure and gene expressions call for further studies.
Subjects
山羊
黃體
組織缺氧
類固醇生合成
血管生成
超微結構
粒線體
Type
thesis
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