Difference inconstitutive heterochromatin behaviour between humanamniocytes and lymphocytes detected byasequential insitu exonuclease IIIdigestion-random primer extension procedure

Fixedchromosomes fromhumanamniotic fluid cells andperipheral bloodlymphocytesweredigested in situwithexonuclease IIIandthesingle stranded DNA obtained wasusedastemplate foranin siturandomprimerextension. Under theseconditions an R bandingpattern, more evidentinlymphocytes thanin amniocytes, wasobtained. Nevertheless, constitutive heterochromatin of chromosomes1,16,Yq,andmainlythepericentromeric region ofchromosome9was farmoreintensely labelled inamniocytes thaninlymphocytes. Fluorescence insitu hybridisation withaspecific classical satellite DNA probe, showedthatthisdifferential labelling wasdependent onagreater sensitivity ofchromosome9 constitutive heterochromatin toexonuclease IIIdigestion inamniocytes thaninlymphocytes,thus indicating qualitative differences inthisregionbetweenboth humancellular materials. (JMedGenet1995;32:32-35)