Transient expression of megakaryocyte-derived protein immunoreactive with an antiserum to cartilage oligomeric matrix protein in developing rat liver
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S Onodera1, Y Tonozuka, S Tashiro
1Department of Clinical and Biomedical Sciences, Showa Pharmaceutical University, Tokyo, 194-8543, Japan. onodera@ac.shoyaku.ac.jp
Abstract:
We analyzed a megakaryocyte-derived protein immunoreactive with an antiserum to cartilage oligomeric matrix protein (COMP) in the developing rat liver. Staining with the anti-COMP antiserum in the developing rat liver increased during embryogenesis, and was strongest in the livers of 17-day-old embryos. However, staining in the liver was not detected at eight days after birth or thereafter. The stained cells were found to be megakaryocytes. We partially purified the protein showing cross-reaction with the antiserum to COMP from a megakaryocyte-rich cells fraction in 17-day-old embrionic rat livers. The molecular weight of this protein (approximately 95 kDa) was close to the molecular weight of COMP (105 kDa). Amplification of an RT-PCR fragment (225 bp) corresponding to part of COMP mRNA was detected in cartilage, but not in megakaryocytes of fetal liver or bone marrow. Based on these results, the fetal rat liver megakaryocyte-derived protein that reacted with the antiserum against COMP was thought to contain a common epitope with COMP from cartilage, but to be a different protein from COMP.
Insights
A novel protein in fetal rat liver megakaryocytes reacts with antibodies to cartilage oligomeric matrix protein (COMP). This megakaryocyte protein shares an epitope with COMP but is distinct from it.
Area of Science:
- Biochemistry
- Developmental Biology
- Hematology
Background:
- Cartilage oligomeric matrix protein (COMP) is a key component of cartilage extracellular matrix.
- Megakaryocytes are bone marrow cells responsible for producing platelets.
- The presence and function of COMP-like proteins in non-cartilaginous tissues are not well understood.
Purpose of the Study:
- To investigate the presence of a COMP-immunoreactive protein in developing rat liver megakaryocytes.
- To characterize the biochemical properties of this protein.
- To determine its relationship to cartilage COMP.
Main Methods:
- Immunohistochemical staining of developing rat liver using anti-COMP antiserum.
- Isolation and partial purification of the immunoreactive protein from megakaryocyte-rich fractions.
- Western blot analysis to determine molecular weight.
- Reverse transcription polymerase chain reaction (RT-PCR) to detect COMP mRNA.
Main Results:
- A COMP-immunoreactive protein was detected in developing rat liver megakaryocytes, peaking at embryonic day 17.
- The protein was partially purified and found to have a molecular weight of approximately 95 kDa, similar to COMP (105 kDa).
- COMP mRNA was detected in cartilage but not in fetal liver or bone marrow megakaryocytes, suggesting the protein is not COMP itself.
Conclusions:
- Developing rat liver megakaryocytes produce a protein that shares an epitope with cartilage COMP.
- This megakaryocyte-derived protein is distinct from cartilage COMP, as indicated by the absence of COMP mRNA in these cells.
- The findings suggest the existence of COMP-related proteins in hematopoietic cells with potential roles in liver development.