家蚕茧丝突变种Nd的丝腺发育形态观察

Morphological Observation of Silk Gland Development in Nd Mutant of Silkworm

裸蛹(Nd:25-0.0)其突变性状表现为绢丝腺退化及不能正常吐丝结茧,基因位于与丝素重链同在的第25号染色体的0.0座位。在本研究中,选用Nd-s及大造作为对照,解剖不同发育时期丝腺,经DAPI染色后计数其丝腺细胞数和观察丝腺细胞的发育情况。蚁蚕时期丝腺细胞数的统计结果表明,3个品种的中部丝腺和后部丝腺在细胞数目上并无显著性差异;而在5龄初期,Nd后部丝腺的发育明显比对照发育慢,特别是在长度上;对丝腺细胞核的染色观察发现,5龄期,Nd突变种的中部丝腺的细胞核分裂与对照相比无差异,均呈树突状分裂;而后部丝腺细胞只发生纵向扩展,无正常家蚕丝腺细胞的树突状分裂。对fib-H基因末端序列测序结果表明,该突变在fib-H末端的半胱氨酸位点也没有发生突变。由此认为,该突变种丝腺的退化并不是真正的细胞数减少或者发育过程中萎缩,而是后部丝腺细胞核的分裂过程发生异常从而造成后部丝腺的短小,推测该突变基因与细胞核的分裂有关。

Nake pupa （Nd：25--O. 0） is a kind of silk mutants preserved by the gene library of our institute. The mutant has a pair of degraded silk gland and about half of the mutant silk- worms fail to spin. According to linkage analysis, Nd is located on the 25th chromosome which contains the fibrin heavy chain gene. In this research, we choose Nd-s and Dazao （p50） as the control, anatomize the silk glands in different developmental stages, take count of the silk gland cells, and observe their growth after DAPI. Silk gland cell count at the newly--hatched silkworm larva stage shows that middle or posterior silk gland（MSG or PSG）cell number of the 3 different species reveals no distinct diversity. In the early 5th instar, the PSG of Nd apparently grows slower than the other 2 contrasts, especially in length, which is only half of the others. According to the nuclear staining observation, in the 5th instar the nucleus of MSG of Nd mutant exhibits a dendrite propagation, just the same as the contrasts, while the nucleus of PSG only expands lengthways, which is different from the natural nucleus of silk gland cell. The sequence analysis of fib-H 3 termination shows that there is no difference at the Cys site between Nd and the control. So we postulate that the degradation of Nd silk gland is not a decrease in cell number or atrophy in growth, but a shortness of PSG caused by a heteroplasia in the cleavage of nucleus. We speculate that the gene is associated with cell nucleus division.