家蚕(Bombyx mori)5龄幼虫丝腺染色质在核基质上的组构

NUCLEAR MATRIX-BASED CHROMOSOMAL ORGANIZATION IN THE 5TH INSTAR LARVAE OF THE SILKWORM,BOMBYX MORI

家蚕(Bombyx mori)5龄幼虫丝腺的染色质高度多倍化,整个基因组达10~5至10~6个拷贝。依次经低盐和高盐抽提5龄幼虫中丝腺、后丝腺和蚕体的细胞核,得到其核晕 (nuclearhalo),限制性内切酶消化后还有一部分DNA片段与核基质紧密结合在一起,说明染色质的组织与核基质有关。通过测定核基质上残留的DNA片段的平均长度及其在全基因组DNA中所占的百分比计算出,核晕上DNAloop的平均大小在中丝腺、后丝腺以及蚕体细胞中均为67kb左右。丝腺中高度多倍化的染色质与二倍体蚕体组织之间并不存在差异,它们同样被错定在核基质上而分隔成长约67kb的染色质loop,从而保证整个基因组的有序排列。以丝素基因为探针进行DNA印迹杂交发现,在5龄后丝腺中丝素基因特异性地和核基质紧密结合,说明核基质与丝素基因的组织特异性表达有关。

The chromosomes in the fifth instar larvae of the silkworm, Bombyx mori are amplified to about 105-106 copies. After the nuclei of middle silkglands(MSG) .posterior silkglands(PSG) and bodies from the 5th instar larvae were ex-tracted with low-salt and high-salt solution.the nuclear halos were harvested. There were stili some DNA fragments associated with the nuclear matrix after coniplete digestion with a variety of restriction endonucleases. This indicated that the chromosomal organization was related to the nuclear matrix. By means of detecting the average length and percentage of matrix-binding DNA fragments, the average length of DNA loops in MSG.PSG and body were count-ed. There is no obvious difference detected among the three parts. The loop size is about 67kb in multineme chromosomes of MSG and PSG cells as well as in diploid body cells. Southern blot of nuclear matrix-binding DNAs with the fibroin gene suggested that the nuclear matrix is also the base for efficient replication and tissue-specific transcription of fibroin gene.