Did you know #2

By John W. Harvey

Did you know that the inactivated X chromosome, seen in a small portion of female neutrophils (nuclear drumstick appendage or sex chromatin lobe) was first recognized by Barr and Bertram in female cat neurons in 1949? Because these structures were associated with the nucleolus, they were called nucleolar satellites; however, they are now called Barr bodies when seen in non-leukocyte cell types and sometimes in neutrophils also. Davidson and Smith reported that drumstick appendages in human neutrophils were sex specific in 1954, with an average of about 3 percent of female neutrophils and no male neutrophils having this specific appendage. Drumstick appendages were defined as being solid, having a round head (about 1.5 mm in diameter), and joined by a fine filament to one lobe of the nucleus (see image of a female cat neutrophil). The number of drumstick appendages in females is directly related to the degree of nuclear segmentation, i.e, a higher percentage is seen in more segmented neutrophils. Drumstick appendages have also been recognized predominantly in neutrophils of female domestic mammals (generally 2-5%); however, they are not reported to differentiate sexes in rodents. Some authors report up to 1% drumsticks in neutrophils of male mammals, including humans. A major difficulty in comparing studies is the criteria used to classify appendages, because other nuclear appendages, including sessile nodules, small clubs, tags, and racket formations can occur in neutrophils from both sexes. Initially, the microscopically visualized sex chromatin was thought to represent both X chromosomes bound together, but subsequent studies demonstrated that the visualized sex chromatin represented hyperchromatic “condensed” chromatin of the inactivated X chromosome. The Y chromosome is small and contains primarily genes responsible for the male phenotype. The X chromosome is larger and contains x-linked genes (including ones for glucose-6-phosphate dehydrogenase, coagulation factor IX, and coagulation factor VIII) in addition to genes responsible for the female phenotype. The random inactivation of one of the two X chromosomes in females results in similar amounts of X-linked protein production in females and males. Learn more here.

The initial description of the Barr body: “Normal motor neuron from the hypoglossal nucleus of a mature female cat showing the usual morphology of the nucleolar satellite (indicated by arrow) In the female. Cresyl violet stain, x 1,400.” From Barr and Bertram, 1949.
Barr body in a feline neutrophil