Nested retrotransposons on the W chromosome of the wild silkworm Bombyx mandarina

Abe, Hiroaki; Sugasaki, Toshiyuki; Terada, Toru; Kanehara, Mariko; Ohbayashi, Fumi; Shimada, Toru; Kawai, Shinya; Mita, Kazuei; Oshiki, Toshikazu

doi:10.1046/j.1365-2583.2002.00339.x

Cited by 22 publications

(24 citation statements)

References 48 publications

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“…Additionally, eleven of twelve female-specific RAPD markers found in B. mori were not found in the W chromosome of B. mandarina (Abe et al, manuscript in preparation). These results indicate that the W chromosome of B. mandarina differs from that of B. mori at the DNA sequence level (Abe et al, 2002). The accumulation of retrotransposable ele-ments in the W chromosomes of B. mori and B. mandarina likely began after the two species separated.…”

Section: Identification Of the Rapd Markers On The W Chromosomementioning

confidence: 83%

Retrotransposable elements on the W chromosome of the silkworm, Bombyx mori

Abe

Mita²,

Yasukochi³

et al. 2005

Cytogenet Genome Res

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The sex chromosomes of the silkworm, Bombyxmori, are designated ZW(XY) for females and ZZ(XX) for males. The W chromosome of B. mori does not recombine with the Z chromosome and autosomes and no genes for morphological characters have been mapped to the W chromosome as yet. Furthermore, femaleness is determined by the presence of a single W chromosome, regardless of the number of autosomes or Z chromosomes. To understand these interesting features of the W chromosome, it is necessary to analyze the W chromosome at the molecular biology level. Initially to isolate DNA sequences specific for the W chromosome as randomly amplified polymorphic DNA (RAPD) markers, we compared the genomic DNAs between males and females by PCR with arbitrary 10-mer primers. To the present, we have identified 12 W-specific RAPD markers, and with the exception of one RAPD marker, all of the deduced amino acid sequences of these W-specific RAPD markers show similarity to previously reported amino acid sequences of retrotransposable elements from various organisms. After constructing a genomic DNA lambda phage library of B. mori we obtained two lambda phage clones, one containing the W-Kabuki RAPD sequence and one containing the W-Samurai RAPD sequence and found that these DNA sequences comprised nested structures of many retrotransposable elements. To further analyze the W chromosome, we obtained 14 W-specific bacterial artificial chromosome (BAC) clones from three BAC libraries and subjected these clones to shotgun sequencing. The resulting assembly of sequences did not produce a single contiguous sequence due to the presence of many retrotransposable elements. Therefore, we coupled PCR with shotgun sequencing. Through these analyses, we found that many long terminal repeat (LTR) and non-LTR retrotransposons, retroposons, DNA transposons and their derivatives, have accumulated on the W chromosome as strata. These results strongly indicate that retrotransposable elements are the main structural component of the W chromosome.

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Section: Identification Of the Rapd Markers On The W Chromosomementioning

confidence: 83%

Retrotransposable elements on the W chromosome of the silkworm, Bombyx mori

Abe

Mita²,

Yasukochi³

et al. 2005

Cytogenet Genome Res

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“…Using primer sets near both ends of the insertion, we were not able to amplify a PCR band from the sch l mutant, even using long-range PCR. We therefore speculated that the insertion fragment was a long complex retrotransposon containing many other transposons and retrotransposons, like those present in W chromosomes (33,34). Using reverse PCR with primer sets near the insertion sites (Table S5), we identified and sequenced amplicons from both ends of the insertion fragment.…”

Section: Resultsmentioning

confidence: 99%

Repression of tyrosine hydroxylase is responsible for the sex-linked chocolate mutation of the silkworm, Bombyx mori

Lei

Yamamoto

Cheng

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

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Pigmentation patterning has long interested biologists, integrating topics in ecology, development, genetics, and physiology. Wild-type neonatal larvae of the silkworm, Bombyx mori , are completely black. By contrast, the epidermis and head of larvae of the homozygous recessive sex-linked chocolate ( sch ) mutant are reddish brown. When incubated at 30 °C, mutants with the sch allele fail to hatch; moreover, homozygous mutants carrying the allele sch lethal ( sch l ) do not hatch even at room temperature (25 °C). By positional cloning, we narrowed a region containing sch to 239,622 bp on chromosome 1 using 4,501 backcross (BC1) individuals. Based on expression analyses, the best sch candidate gene was shown to be tyrosine hydroxylase ( BmTh ). BmTh coding sequences were identical among sch , sch l , and wild-type. However, in sch the ∼70-kb sequence was replaced with ∼4.6 kb of a Tc1-mariner type transposon located ∼6 kb upstream of BmTh , and in sch l , a large fragment of an L1Bm retrotransposon was inserted just in front of the transcription start site of BmTh . In both cases, we observed a drastic reduction of BmTh expression. Use of RNAi with BmTh prevented pigmentation and hatching, and feeding of a tyrosine hydroxylase inhibitor also suppressed larval pigmentation in the wild-type strain, pnd + and in a pS (black-striped) heterozygote. Feeding L-dopa to sch neonate larvae rescued the mutant phenotype from chocolate to black. Our results indicate the BmTh gene is responsible for the sch mutation, which plays an important role in melanin synthesis producing neonatal larval color.

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“…Clusters of mtanga, a retrotransposon that is actively expressed on the Y chromosome in Anopheles gambiae, were detected by Rohr et al (2002). The results from Abe et al (2002) indicate that retrotransposons accumulate gradually as strata without recombination on the W chromosome of Bombyx mandarina. Further, Underwood and Bianco (1999) detected a molecular marker, designated TOY, for the Y chromosome of the filarial nematode Brugia malayi.…”

Section: Accumulation Of Retrotransposons On Y Chromosomes: a Generalmentioning

confidence: 94%

Retroelements: tools for sex chromosome evolution

Steinemann

2005

Cytogenet Genome Res

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Many eukaryotic taxa inherit a heteromorphic sex chromosome pair. It is a generally accepted hypothesis that the sex chromosome pair is derived from a pair of homologous autosomes that has developed after the occurrence of a sex differentiator in an evolutionary process into two structurally and functionally different partners. In most of the analyzed systems the occurrence of the dominant sex differentiator is paralleled by the suppression of recombination within and close by that region. The recombinational isolation can spread in an evolutionary selection process from neighboring regions finally over the whole chromosome. Suppression of recombination strongly biases the distribution of retrotransposons in the genome. Our results and that from others indicate that the major force driving the evolution of Y chromosomes are retrotransposons, remodeling euchromatic chromosome structures into heterochromatic ones. In our model, intact or already eroded retrotransposons become trapped due to their inherent transposition mechanisms in non-recombining regions. The massive accumulation of retrotransposons interferes strongly with the activity of genes. We hypothesize that Y chromosome degeneration is a stepwise evolutionary process: (1) Massive accumulation of retrotransposons occurs in the non-recombining regions. (2) Heterochromatic nucleation centers are formed as a consequence of genomic defense against invasive parasitic elements; the established nucleation centers become epigenetically inherited. (3) Spreading of heterochromatin from the nucleation centers into flanking regions induces in an adaptive process gene silencing of neighbored genes that could either be still intact or in an already eroded condition, e.g., showing point mutations, deletions, insertions; the retroelements should be subjects to the same forces of deterioration as the genes themselves. (4) Constitutive silenced genes are not committed to the same genetic selection pressure as active genes and therefore more exposed to the decay process. (5) Gene dosage balance is reestablished by the parallel evolution of dosage compensation mechanisms. The evolving secondary sex chromosomes, neo-X and neo-Y, of Drosophila miranda are revealed to be a unique and potent model system to catch the evolutionary Y deterioration process in progress.

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Nested retrotransposons on the W chromosome of the wild silkworm Bombyx mandarina

Cited by 22 publications

References 48 publications

Retrotransposable elements on the W chromosome of the silkworm, <i>Bombyx mori</i>

Retrotransposable elements on the W chromosome of the silkworm, <i>Bombyx mori</i>

Repression of tyrosine hydroxylase is responsible for the sex-linked chocolate mutation of the silkworm, Bombyx mori

Retroelements: tools for sex chromosome evolution

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