Cdr2, or cerebellar degeneration-related protein 2, is an onconeural antigen with multiple functions. In fission yeast cells, it forms membrane-bound nodes during interphase. These nodes are crucial for timely cell cycle progression, positioning of the cytokinetic ring, and controlling cell size at division [3,4,5,6]. In mammalian cells, it may be involved in regulating ER sheet organization as a dynein adaptor recruited by kinectin [8]. It is also associated with paraneoplastic neurological disorders, especially Purkinje cytoplasmic autoantibody type 1 (PCA-1)/anti-Yo paraneoplastic autoimmunity [1,2,7,9].

In the context of PCA-1/anti-Yo autoimmunity, single-modality CDR2 testing can produce false-positive results. However, when combined with testing for CDR2L, the sensitivity and specificity of detecting PCA-1/Yo autoimmunity can be optimized. In serum, requiring both CDR2 and CDR2L positivity achieves high sensitivity (100%) and specificity (99.9%), and in cerebrospinal fluid (CSF), CDR2L positivity alone provides high sensitivity (100%) and specificity (99.6%) [1]. In paraneoplastic cerebellar degeneration, CDR2 localizes to the nucleus and co-localizes with nuclear speckle proteins like SON, eukaryotic initiation factor 4A-III, and serine/arginine-rich splicing factor 2, potentially interfering with mRNA translation and protein synthesis [9].

In conclusion, Cdr2 is essential for cell cycle regulation, cell size control in fission yeast, and may play a role in ER organization in mammalian cells. In paraneoplastic neurological disorders, understanding its relationship with CDR2L is crucial for accurate diagnosis. Studies on Cdr2 contribute to our understanding of biological processes and disease mechanisms, especially in paraneoplastic cerebellar degeneration.