Keeping chromatin in a stable state is essential for genome stability, scheduled transcription, replication, DNA repair, and precise and reliable chromosome segregation and telomere maintenance during cell division. Over the past decade, research on chromatin remodeling has made great strides whereby modification of histone proteins is a key factor involved in many of the essential cellular processes. The nuclear findings of tumor cells that pathologists routinely examine are nothing but reflections of both genomic and histone alterations. Moreover, impaired histone function is known to be related to common diseases such as diabetes and atherosclerosis, and is, therefore, considered a potential therapeutic target. The present review first outlines the physiological function of histone proteins, and second, demonstrates their alterations to pathological states, emphasizing the importance of immunohistochemistry in histopathological diagnosis.

In situ hybridization (ISH), which visualizes nucleic acids in tissues and cells, is a powerful tool in histology and pathology. Over 50 years since its invention, multiple attempts have been made to increase the sensitivity and simplicity of these methods. Therefore, several highly sensitive in situ hybridization methods have been developed that offer researchers a wide range of options. When selecting these in situ hybridization variants, their signal-amplification principles and characteristics must be understood. In addition, from a practical point of view, a method with good monetary and time-cost performance must be chosen. This review introduces recent high-sensitivity in situ hybridization variants and presents their principles, characteristics, and costs.

In the course of SRY-box transcription factor 6 (SOX6) expression profiling in human embryonic tissue, SOX 6 was found to be highly expressed in the notochord, based on the findings of immunohistochemistry (IHC). Sox6 is also expressed in the neural tube and the distribution of SOX6 is located in the ventral and dorsal zones of the neural tube. In contrast to the findings that SOX6-positive cells were located on the floor plate of the neural tube, OLIG2- and NKX2.2-expressing cells were lacking on the floor plate of the neural tube, and their expression was restricted only to the ventral zone of the neural tube. The expression patterns of SOX9 were similar to those of OLIG2 and NKX2.2 in the neural tube. NKX2.2 and OLIG2 are not expressed in the notochord, but SOX9 and SOX6 are. Because Sox6 is highly expressed in the notochord, the present study investigated whether or not SOX6 is an immunohistochemical marker for the pathologic diagnosis of chordoma, a neoplasm derived from the notochord. IHC revealed that chordoma was strongly positive for SOX6 in two cases of chordoma, one of which occurred in the sacrococcygeal region and another that developed at the base of the skull, suggesting that SOX6 is a useful marker for the histopathologic diagnosis of chordoma.