Acts as a transcriptional repressor through interaction with histone deacetylases (HDACs). May regulate haploid genes important for spermiogenesis. Interacts with HDAC1, HDAC3, HDAC6 and, to a lesser extent, with HDAC7. In step 9-11 spermatids, shifts from nucleus to cytoplasm. Testis-specific. Expressed in pachytene spermatocytes and all developing spermatids, but not in Sertoli, nor Leydig cells (at protein level). At the mRNA level, first detected in early pachytene spermatocytes. At the protein level, first detected in step 2 round spermatids. Expression continuously increases thereafter and peaks in spermatids at steps 7-9 (at protein level). Levels start to decrease after step 9 and in step 9-11 elongating spermatids (at protein level). Since CXCL16 and ZMYND15 genes overlap in their 5'UTRs, CXCL16 knockout also disrupts the ZMYND15 gene. The double knockout mice display severe depletion of late spermatids and are thus infertile. This phenotype is probably due to ZMYND15, rather than CXCL16, deficiency.