HISTONE H3 MESSENGER-RNA IN-SITU HYBRIDIZATION CORRELATES WITH IN-VIVO BROMODEOXYURIDINE LABELING OF S-PHASE CELLS IN RAT COLONIC EPITHELIUM

Measurements of cell cycle phase fractions, particularly S-phase, are useful for studies of cell biology and carcinogenesis, Up-regulation o f histone gene expression is tightly coupled to the G(1)-S-phase trans ition of the cell cycle, and mRNA levels rise 30-100-fold during S-pha se, Labeling of histone H3 mRNA using in situ hybridization (ISH) was assessed as a measure of S-phase cells and compared with that found us ing in vivo 5-bromodeoxyuridine (BrdUrd) labeling in formalin-fixed ra t colonic crypts under baseline, modified 72-h starvation, and 24-h re feeding conditions. The labeling index scored in single-labeled sectio ns by histone H3 ISH tightly correlated with that found by in vivo Brd Urd labeling (r = 0.99, P < 0.0001) and clearly discriminated between the control, starved, and refed states (P < 0.001). In 180 crypt secti ons double labeled using histone H3 ISH and BrdUrd, 92% of 1572 labele d cells exhibited both nuclear BrdUrd and cytoplasmic histone H3 label , It is concluded that histone H3 ISH is an accurate measure of the S- phase fraction and provides an alternative to in vivo BrdUrd labeling in fat colon. This finding warrants validation in human studies.