Clones and X-chromosomes

X-inactivation and the dynamic maintenance of gene silencing

X-inactivation has long been a topic of fascination for educators, researchers, and clinicians alike. From complex patterns of inheritance to phenotypic variation among females with X-linked traits, a myriad of hypothesis and interpretations exist. Once thought to be random yet complete, X-inactivation has proven itself the poster child of the exception rather than the rule. Indeed, patterns of X-inactivation are all too often non-random, and many X-linked genes are capable of escaping X-inactivation. Similarly, X-inactivation is well-known for being stably maintained for life, but some previously inactivated X-linked genes reactivate with increasing age. Moreover, recent papers illustrate that X-inactivation can be challenged in other ways, thereby rendering the stability of X-inactivation compromised. This review describes factors involved in the maintenance of X-inactivation as we know it and discusses these emerging data that suggest a more dynamic model of the maintenance of X-inactivation may be in order.

The utility of some modern techniques in understanding thyroid pathology

A number of evaluating techniques have moved from the research laboratory into the purview of the diagnostic pathologist and have been applied to the analysis of thyroid lesions. Some of these have already proved diagnostically and prognostically useful, whereas some have produced insights into pathogenesis of specific thyroid lesions and disorders. Rapid proliferation and application of these techniques should allow for increased understanding of human thyroid disease in the near future.