Calreticulin is a calcium-dependent ER chaperone, involved in protein folding, maturation, and cellular localization. Calreticulin is a highly conserved 48 kDa protein encoded by the CALR gene. Calreticulin and its homolog calnexin regulate the folding and degradation of newly synthesized glycoproteins as they are translocated into the ER (1). Misfolded proteins recognized by calreticulin are targeted to the ER-associated degradation (ERAD) pathway. Within the ER, calreticulin also plays an important role in calcium homeostasis. Calreticulin has also been identified outside of the ER and plays unique roles in each subcellular compartment. On the cell surface, calreticulin interacts with thrombospondin (TSP) to promote disassembly of focal adhesion complexes and cellular migration (2). Calreticulin on the cell surface of phagocytic cells acts as receptor for C1q and mediates the uptake of apoptotic cells. Calreticulin plays an important role in downregulating protein expression and localization to the cell surface. Calreticulin has been implicated in many autoimmune and malignant pathologies.
In 2002, Somogyi et. al. used the Calreticulin antibody to prove that calreticulin expression was not limited to the ER (3). The group used the Calreticulin antibody to localize calreticulin within cells of developing rat molars as well as adult rat incisors. The group found that calreticulin was localized to the predentin and odontoblasts, suggesting a role in early development. Further studies with the Calreticulin antibody led the group to confirm calreticulin expression in the ER, nucleus, and cytoplasm.
Ramos et. al. used the Calreticulin antibody to assess expression and localization of calreticulin during oogenesis and embryogenesis of the insect Rhodnius prolixus (4). Western blot studies with the Calreticulin antibody confirmed expression in the developing oocytes and eggs. Immunofluorescence studies showed enriched Calreticulin expression in the peripheral cortex. The authors suggest that these results will lay the groundwork for further investigation into the programming and development of R. prolixus.
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