W chromosome sequences of two bombycid moths provide an insight into the origin of Fem.

Fem is a W-linked gene that encodes a piRNA precursor, and its product, Fem piRNA, is a master factor of female determination in Bombyx mori. Fem has low similarity to any known sequences, and the origin of Fem remains unclear. So far, two hypotheses have been proposed for the origin of Fem: The first hypothesis is that Fem is an allele of Masc, which assumes that the W chromosome was originally a homologous chromosome of the Z chromosome. The second hypothesis is that Fem arose by the transposition of Masc to the W chromosome. To explore the origin of Fem, we determined the W chromosome sequences of B. mori and, as a comparison, a closely relative bombycid species of Trilocha varians with a Fem-independent sex determination system. To our surprise, although the sequences of W and Z chromosomes show no homology to each other, a few pairs of homologues are shared by W and Z chromosomes, indicating the W chromosome of both species originated from Z chromosome. In addition, the W chromosome of T. varians lacks Fem, while the W chromosome of B. mori has over 100 copies of Fem. The high-quality assembly of the W chromosome of B. mori arose the third hypothesis about the origin of Fem: Fem is a chimeric sequence of multiple transposons. More than half of one transcriptional unit of Fem shows a significant homology to RTE-BovB. Moreover, the Fem piRNA-producing region could correspond to the boundary of the two transposons, gypsy and satellite DNA.

Male-killing virus in a noctuid moth Spodoptera litura.

A female-biased sex ratio is considered advantageous for the cytoplasmic elements that inhabit sexually reproducing organisms. There are numerous examples of bacterial symbionts in the arthropod cytoplasm that bias the host sex ratio toward females through various means, including feminization and male killing. Recently, maternally inherited RNA viruses belonging to the family Partitiviridae were found to cause male killing in moths and flies, but it was unknown whether male-killing viruses were restricted to Partitiviridae or could be found in other taxa. Here, we provide compelling evidence that a maternally inherited RNA virus, Spodoptera litura male-killing virus (SlMKV), selectively kills male embryos of the tobacco caterpillar Spodoptera litura, resulting in all-female broods. SlMKV injected into uninfected S. litura can also be inherited maternally and causes male killing. SlMKV has five genomic segments encoding seven open reading frames, has no homolog of known male-killing genes, and belongs to an unclassified group of arthropod-specific viruses closely related to Tolivirales. When transinfected into larvae, both male and female recipients allow SlMKV to proliferate, but only males die at the pupal stage. The viral RNA levels in embryonic and pupal male killing suggest that the mechanism of male killing involves the constitutive expression of viral products that are specifically lethal to males, rather than the male-specific expression of viral products. Our results, together with recent findings on male-killing partiti-like viruses, suggest that diverse viruses in arthropods tend to acquire male killing independently and that such viruses may be important components of intragenomic conflict in arthropods.

Unique sex determination system in the silkworm, Bombyx mori: current status and beyond.

The silkworm Bombyx mori has been used for silk production for over 5,000 years. In addition to its contribution to sericulture, B. mori has played an important role in the field of genetics. Classical genetic studies revealed that a gene(s) with a strong feminizing activity is located on the W chromosome, but this W-linked feminizing gene, called Feminizer (Fem), had not been cloned despite more than 80 years of study. In 2014, we discovered that Fem is a precursor of a single W chromosome-derived PIWI-interacting RNA (piRNA). Fem-derived piRNA binds to PIWI protein, and this complex then cleaves the mRNA of the Z-linked Masculinizer (Masc) gene, which encodes a protein required for both masculinization and dosage compensation. These findings showed that the piRNA-mediated interaction between the two sex chromosomes is the primary signal for the sex determination cascade in B. mori. In this review, we summarize the history, current status, and perspective of studies on sex determination and related topics in B. mori.

Conservation and lineage-specific rearrangements in the GOBP/PBP gene complex of distantly related ditrysian Lepidoptera.

General odorant binding proteins (GOBPs) and pheromone binding proteins (PBPs) form a monophyletic subfamily of insect odorant binding proteins (OBPs) specific for Lepidoptera, butterflies and moths. The GOBP/PBP genes include six subgroups (GOBP1-2, PBP-A-D) previously reported to form a complex arrayed in a conserved order in representative moths (superfamily Bombycoidea) and butterflies (Nymphalidae). Although our knowledge of lepidopteran genomes has increased greatly recently, the structure of the GOBP/PBP complex has been studied only for species that represent limited lineages of the highly diverged Ditrysia. To understand the evolution of this functionally important gene complex, we determined 69-149 kb genomic sequences that include GOBP2 and five PBP genes in three Ostrinia moths (Pyraloidea), O. nubilalis, O. furnacalis, and O. latipennis, using bacterial artificial chromosome (BAC) and fosmid clones. The structure of the GOBP2/PBP gene cluster was well conserved despite the different sex pheromone composition utilized by the three moths. Five expressed PBP genes in Ostrinia moths were the result of two duplications of PBP-A genes. Surprisingly, an allele containing a fusion gene between tandemly arrayed PBP-A genes was observed in O. nubilalis. We also revealed duplication and intra-chromosomal translocation of the GOBP1 gene in P. xylostella by fluorescence in situ hybridization (FISH) analysis. Additionally, we compared the structure of the GOBP/PBP gene complex of seventeen species covering six superfamilies and twelve families of the lepidopteran clade, Ditrysia, and found the gene order was basically conserved despite the frequent occurrence of lineage-specific gains, losses, inversions and translocations of these genes, compared with their neighboring genes. Our findings support the hypothesis that the structure of the GOBP/PBP gene complex was already established in the common ancestor of Ditrysia.

Evaluation of intratumoral hemodynamics with color Doppler imaging in patients with colorectal carcinoma: comparison between waveform analysis and histopathologic characteristics.

PURPOSE: We studied the relation between intratumoral hemodynamics and histopathologic characteristics in patients with colorectal carcinoma. METHODS: A series of 82 patients with 28 well-differentiated adenocarcinomas, 40 moderately differentiated adenocarcinomas, 10 poorly differentiated adenocarcinomas, and 4 mucinous adenocarcinomas underwent color Doppler examination and surgical treatment. The waveform of blood flow in the thickened wall of the colon was analyzed by determining the maximum velocity (Vmax) and resistance index (RI). These parameters were compared with histopathologic findings of the resected specimens: gross form, tumor size, depth of invasion, histologic stage, and histopathologic classification. RESULTS: Both Vmax and RI were higher in the invasive tumors rather than the expansive ones. Vmax and tumor size were not correlated; however, the RI increased proportionately with tumor size in tumors larger than 4 cm in diameter. Both parameters increased with depth of invasion and histologic stage through stage IIIb. Both were markedly higher in mucinous adenocarcinomas than in the other histopathologic types. Furthermore, Vmax in well, moderately, and poorly differentiated adenocarcinomas did not differ significantly, although RI was negatively associated with the degree of differentiation. CONCLUSIONS: We concluded that blood-flow analysis is closely associated with histopathologic findings of colorectal carcinomas and that it provides information useful in the clinical management of these patients.

Proximal bifurcation of hepatic artery: Novel findings on hepatic arteries demonstrated by ultrasound Doppler imaging, B-flow, and US angiography.

PURPOSE: It has generally been held that each portal branch is always accompanied by a single arterial branch in the liver. During Doppler ultrasound examination, however, we sometimes encounter a portal branch that appears to be associated with two arterial branches, a phenomenon referred to below asthis finding orthis phenomenon. Here we attempt to confirm that this finding is based on a correct interpretation of the image and to disclose its basic mechanism. MATERIAL AND METHODS: Five cases of chronic liver disease in which this phenomenon appeared were analyzed with B-flow imaging. Videotapes obtained from 30 patients who had chronic liver disease and had undergone ultrasound angiography (USAG) with arterial infusion of CO2 micro bubbles were reviewed in order to look for similar findings. Sixty-nine healthy controls were also examined with Doppler sonography for this purpose. Histopathologic specimens from 7 patients who had undergone hepatectomy (3 with hepatocellular carcinoma, 3 with metastatic tumor, and 1 with focal nodular hyperplasia) were examined to study the basic structure of the hepatic vessels. RESULTS AND DISCUSSION: Three parallel color signals (two pulsatile and one of a constant waveform) observed on Doppler examination were confirmed by the B-flow method to be three independent vessels in all five cases in which both Doppler sonography and B-flow imaging were used. In 13 (43%) of the 30 cases of USAG, two vessels along a portal branch were visualized by the inflow of micro bubbles, indicating that the two vessels were arteries. The trio of one portal and two arterial branches was also detected with Doppler sonography in 12 (17%) of the 69 healthy controls. In 10 (59%) of the 17 cases (5 of liver disease and 12 normal) that showed this finding on Doppler examination, bifurcations of the hepatic artery and portal vein were both visualized. Hepatic arterial branches were found to bifurcate slightly more proximal to the hepatic hilus than the accompanying portal branch. Histopathologic study revealed Glisson's areas that contained one portal branch and two arterial vessels in nontumorous parts of specimens from all 7 patients with hepatectomy. CONCLUSION: Two arterial branches can be demonstrated along a portal branch as a result of a more-proximal bifurcation of the hepatic artery than of the portal vein.