※ Cajal body introduction

    Cajal bodies is a kind of non-membrane-bound nuclear bodies, formation of such sub-organelles usually involves dynamic processes, which can move within the nucleoplasm except when transiently immobilized through interaction with chromatin (1). The Cajal body has been suggested to be associated with telomere maintenance and maturation of the splicing machinery and processing of histone mRNA (2;3), it is rich in ribonucleoprotein (RNP) complexes and characterized by the marker protein coilin that interacts with many factors and thereby serves as a platform for the assembly of Cajal bodies (1). WRAP53β has been demonstrated to be an essential Cajal Body Component, it guides SMN across the cell to Cajal Bodies, and phosphorylation of WRAP53β by ATM promotes its involvement in the DNA damage response (4). besides, Fam118 is a newly identified component of Cajal bodies that is required for Cajal body formation (5). Defects in Cajal body formation are linked to impaired cell proliferation and splicing (6). In fact, Cajal bodies are not essential in telomerase function and telomere elongation ,whereas certain Cajal body factors such as WRAP53β clearly play important roles in telomere homeostasis (1).

References
1. Henriksson, S., & Farnebo, M. (2015) On the road with WRAP53beta: guardian of Cajal bodies and genome integrity. Front Genet, 6, 91. PMID: 25852739
2. Machyna, M., Heyn, P., & Neugebauer, K. M. (2013) Cajal bodies: where form meets function. Wiley Interdiscip Rev RNA, 4(1), 17-34. PMID: 23042601
3. Hutten, S., Chachami, G., Winter, U., Melchior, F., & Lamond, A. I. (2014) A role for the Cajal-body-associated SUMO isopeptidase USPL1 in snRNA transcription mediated by RNA polymerase II. J. Cell. Sci., 127(Pt 5), 1065-1078. PMID: 24413172
4. Coucoravas, C., Dhanjal, S., Henriksson, S., Bohm, S., & Farnebo, M. (2017) Phosphorylation of the Cajal body protein WRAP53beta by ATM promotes its involvement in the DNA damage response. RNA Biol., 14(6), 804-813. PMID: 27715493
5. Li, Y., Fong, K. W., Tang, M., Han, X., Gong, Z., Ma, W, Chen, J. (2014) Fam118B, a newly identified component of Cajal bodies, is required for Cajal body formation, snRNP biogenesis and cell viability. J. Cell Sci., 127(Pt 9), 2029-2039. PMID:24569877
6. Lemm, I., Girard, C., Kuhn, A. N., Watkins, N. J., Schneider, M., Bordonne, R., & Luhrmann, R. (2006) Ongoing U snRNP biogenesis is required for the integrity of Cajal bodies. Mol. Biol. Cell, 17(7), 3221-3231. PMID:16687569