5-Azadeoxycytidine induced heteromorphic undercondensation in the C-blocks of X chromosomes of three mammalian species, Pipistrellus abramus, Millardia meltada, and Apodemus argenteus

Okada Michitada, Obara Yoshitaka, Tsuchiya Kimiyuki

doi:10.11352/scr.17.3

5-azadeoxycytidine (5-aza-dC)-induced undercondensation (UC) was described with cultured lung fibroblasts from three mammalian species, Pipistrellus abramus, Millardia meltada, and Apodemus argenteus, all of which carry a large amount of C-heterochromatin (C-block) on their X chromosomes. The C-blocks were GC-rich in P. abramus, AT/GC-balanced in M. meltada, and AT-rich in A. argenteus, as revealed by fluorescent staining with quinacrine mustard (QM) and chromomycin A₃ (CMA). P. abramus conspicuously undercondensed, irrespective of autosomes or gonosomes, in all C-band regions including C-blocks. The extent of UC was most prominent in P. abramus, rather weak in M. meltada, and weakest in A. argenteus, suggesting a close relation to the amount of GC base pairs contained in C-heterochromatin. Thus 5-aza-dC treatment may be an easy method for detecting GC-rich heterochromatin. The appropriate condi-tions for inducing UC in the C-blocks were 10^-5-10^-6 M and 2-3 hours. The decondensing effect of 5-aza-dC on the C-blocks was time- and concentration-dependent in all species examined, asynchronously acting with certain time lag between the early-replicating X and late-replicating X. The heteromorphic UC between the C-blocks of the XX homologue was observed with a frequency of 8% at maximum, reflecting the allocyclic behavior of the C-blocks.

5-Azadeoxycytidine induced heteromorphic undercondensation in the C-blocks of X chromosomes of three mammalian species, <i>Pipistrellus abramus</i>, <i>Millardia meltada</i>, and <i>Apodemus argenteus</i>

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