We previously studied the phenomena of the mesenchymal cell-dependent mode of cartilage growth in quail and catfish. Thus, we selected the two cartilage models in which mesenchymal cells participate in their growth. In such models, cartilage degradation occurred to facilitate cellular invasion. The studies do not explain the nature of the cartilage degrading cells. The current study aims to explore the nature of the cartilage-degrading cells using transmission electron microscopy (TEM) and immunohistochemistry. Samples of cartilage have been isolated from the air-breathing organ of catfish and the cartilage of the prospective occipital bone of quail embryos. Samples have been processed for TEM and immunohistochemistry. We found that two different cell types are involved in cartilage degradation; the macrophage in the cartilage of catfish and mesenchymal cells in the cartilage of the quail. Areas of cellular invasion in both catfish cartilage and quail embryo cartilage had an immunological affinity for MMP-9. In catfish, cartilage-degrading cells had identical morphological features of macrophages, whereas in quail embryos, cartilage-degrading cells were mesenchymal-like cells which had cell processes rich in vesicles and expressed CD117. Further study should consider the role of macrophage and mesenchymal cells during cartilage degradation. This could be valuable to be applied to remove the defective cartilage matrix formed in osteoarthritic patients to improve cartilage repair strategies.

Relatively little information is available on the local factors that regulate folliculogenesis in goats. To examine the possibility that the Kit ligand (KL) system is expressed throughout the folliculogenesis, we studied the presence and distribution of KL and its receptor, c-Kit, in goat ovaries. Ovaries of goats were collected and either fixed in paraformaldehyde for immunohistochemical localization of KL and c-Kit proteins, or used for the isolation of follicles, luteal cells, surface epithelium and medullary samples to study mRNA expression for KL and c-Kit, using the reverse transcriptase polymerase chain reaction (RT-PCR). KL protein and mRNA were found in follicles at all stages of development, i.e. primordial, primary, secondary, small and large antral follicles, as well as in corpora lutea, surface epithelium and medullary tissue. Antral follicles expressed both KL-1 and KL-2 mRNAs, while earlier staged follicles expressed KL-1 transcript only. KL protein was demonstrated in granulosa cells from the primordial follicle onward. Its mRNA could be detected in granulosa cells isolated from antral follicles and occasionally in their theca cells. c-Kit mRNA was expressed in all antral follicular compartments and at all stages of follicular development. c-Kit protein was predominantly found in oocytes from the primordial follicle stage onwards, in theca cells of antral follicles, as well as in corpora lutea, surface epithelium and medullary tissue, particularly in the wall of blood vessels, which may indicate these cells as the main sites of action of KL. It is concluded that the KL/c-Kit system, in goat ovaries, is widespread and that it may be involved in the regulation of various local processes, including folliculogenesis and luteal activity.