Horizontal gene transfers from eubacteria to lepidopeteran insects during evolution : Mechanism and and biological significance.

在遥远的物种之间进行水平或横向的基因转移在细菌中很常见。然而，在真核生物中，除了少数例外，水平基因转移还没有报道：Mita等人。(2003)报道了在BYX EST数据库中发现的几个编码几丁质酶(Bmchi-h)、蔗糖酶(β-呋喃果糖苷酶)、甘油磷酸二酯酶(GlpQ)和葡萄糖-L-磷酸酶的基因，与细菌的同源性高于与真核生物的同源性。其中，Bmchi-h已被定位到家蚕染色体上(Daimon等人，2003年)。这些都是鳞翅目昆虫和细菌之间水平基因转移的候选对象。本研究进一步分析了BmCHI-h的酶学性质，在出生的BYX和其他鳞翅目昆虫基因组中不仅存在细菌来源的基因，还存在杆状病毒来源的基因。Friesen和Nissen(1990)报道了来自Ni毛霉的“TED”元件的存在，它包含三个开放阅读框架，两侧是ltrs。第三个ORF与第二类杆状病毒囊膜融合蛋白基因(如LdNPV中的ORF 130)同源。它的结构与包括吉普赛人在内的果蝇内源性逆转录病毒相似。我们发现，不仅毛霉菌，而且家蚕也携带逆转录病毒样分子。EST和全基因组鸟枪序列似乎包含至少5个逆转录病毒样元件，其最终的ORF编码ENV样蛋白。我们还发现了12个基因组DNA片段序列，与家蚕线粒体DNA具有很强的同源性。这是第一个证明家蚕基因组已经整合了线粒体DNA的证据。

Horizontal or lateral gene transfers between distantly separated species are common in bacteria. In eukaryotes, however, horizontal gene transfers have not been reported with a few exceptions : Mita et al. (2003) reported that several genes found in the Born byx EST database that encode a chitinase (BmChi-h), sucrase (beta-fructofuranosidase), glycerophosphoryl phosphodiesterase (GlpQ), and glucose-l-phosphatase, show higher homology to bacteria than to eukaryotes. Among these, BmChi-h has been mapped to the silkworm chromosome (Daimon et al., 2003). These are candidates for horizontal gene transfer between lepidopterans and bacteria. The enzymatic properties of BmChi-h were further analyzed in this study.Not only are there bacterium-derived genes, but also baculovirus-derived genes in the Born byx and other lepidopteran genomes. Friesen and Nissen (1990) reported the presence of the "TED" element from Trichoplusia ni, which contains three open reading frames flanked by LTRs. The third ORF is homologous to the gene for envelope fusion proteins (e. g., ORF 130 in LdNPV) in Class II baculoviruses. Its structure is similar to Drosophila endogenous retroviruses, including gypsy. We found that not only Trichoplusia but also Bombyx carries retrovirus-like elements. The EST and the whole-genome shotgun sequences seem to contain at least 5 families of retrovirus-like elements, whose final ORFs encode ENV-like proteins.We also found 12 fragmental sequences of genomic DNA that show strong homology to mitochondrial DNA of Bombyx mori. This is the first evidence indocating the Bombyx genome has incorporated mitochondrial DNA.