Chatterjee R N, Chatterjee P, Pal A, Pal-Bhadra M
Department of Zoology, University of Calcutta, 35 B. C. Road, Kolkata, India.
J Genet. 2007 Dec;86(3):203-15. doi: 10.1007/s12041-007-0028-5.
The Drosophila simulans Lhr rescues lethal hybrids from the cross of D. melanogaster and D. simulans. We describe here, the phenotypes of Lhr dependent rescue hybrids and demonstrate the effects of Lhr on functional morphology of the salivary chromosomes in the hybrids. Our results reveal that the phenotypes of the 'Lhr dependent rescued' hybrids were largely dependent on the genetic background and the dominance in species and hybrids, and not on Lhr. Cytological examination reveal that while the salivary chromosome of 'larval lethal' male carrying melanogaster X chromosome was unusually thin and contracted, in 'rescued' hybrid males (C(mel)X(mel)Y(sim); A(mel)A(sim)) the X chromosome showed typical pale staining, enlarged diameter and incorporated higher rate of (3)H-uridine in presence of one dose Lhr in the genome. In hybrid males carrying simulans X chromosome (C(mel)X(sim)Y(mel); A(mel)A(sim)), enlarged width of the polytene X chromosome was noted in most of the nuclei, in Lhr background, and transcribed at higher rate than that of the single X chromosome of male. In hybrid females (both viable, e.g., C(mel)X(mel)X(sim); A(mel)A(sim) and rescued, e.g., C(mel)X(mel)X(mel); A(mel)A(sim)), the functional morphology of the X chromosomes were comparable to that of diploid autosomes in presence of one dose of Lhr. In hybrid metafemales (C(mel)X(mel)X(mel)X(sim); A(mel)A(sim)), two dose of melanogaster X chromosomes and one dose of simulans X chromosome were transcribed almost at 'female' rate in hybrid genetic background in presence of one dose of Lhr. In rescued hybrid males, the melanogaster-derived X chromosome appeared to complete its replication faster than autosomes. These results together have been interpreted to have suggested that Lhr suppresses the lethality of hybrids by regulating functional activities of the X chromosome(s) for dosage compensation.
拟果蝇的Lhr基因可挽救黑腹果蝇和拟果蝇杂交产生的致死性杂种。我们在此描述了依赖Lhr基因挽救的杂种的表型，并展示了Lhr基因对杂种唾液腺染色体功能形态的影响。我们的结果表明，“依赖Lhr基因挽救”的杂种的表型很大程度上取决于遗传背景以及物种和杂种中的显性关系，而非Lhr基因。细胞学检查显示，携带黑腹果蝇X染色体的“幼虫致死”雄性的唾液腺染色体异常细且收缩，而在“挽救”的杂种雄性（C(mel)X(mel)Y(sim); A(mel)A(sim)）中，在基因组中存在一剂Lhr基因的情况下，X染色体呈现典型的淡染色、直径增大且掺入(3)H-尿苷的速率更高。在携带拟果蝇X染色体的杂种雄性（C(mel)X(sim)Y(mel); A(mel)A(sim)）中，在Lhr基因背景下，大多数细胞核中的多线X染色体宽度增大，且转录速率高于雄性的单条X染色体。在杂种雌性（均存活，例如C(mel)X(mel)X(sim); A(mel)A(sim)和挽救的，例如C(mel)X(mel)X(mel); A(mel)A(sim)）中，在存在一剂Lhr基因的情况下，X染色体的功能形态与二倍体常染色体相当。在杂种超雌（C(mel)X(mel)X(mel)X(sim); A(mel)A(sim)）中，在存在一剂Lhr基因的杂种遗传背景下，两条剂量的黑腹果蝇X染色体和一条剂量的拟果蝇X染色体几乎以“雌性”速率转录。在挽救的杂种雄性中，源自黑腹果蝇的X染色体似乎比常染色体更快地完成其复制。这些结果综合起来表明，Lhr基因通过调节X染色体的功能活性以进行剂量补偿来抑制杂种的致死性。
