Identification of a female determinant gene for the sexual determination of a hemipteran insect, the brown planthopper

The sex determination mechanism for hemipteran species remains poorly understood. During the sex determination of the brown planthopper (BPH), Nilaparvata lugens, one species of Hemiptera, the functions of doublesex (Nldsx) and NlTra-2 (NlTra-2) genes were identified in our previous studies. Here, we identify an upstream gene for Nldsx in the sex determination cascade, NlFmd, which acts as female determinant gene for N. lugens. The sex-specific transcript of NlFmd (NlFmd-F) encodes an arginine/serine-, and proline-rich protein that is essential for female development. The knockdown of NlFmd resulted in the development of pseudomales, with sex-specific alternative Nldsx processing, and maternal RNA interference (RNAi) against NlFmd generates male-only progeny. Moreover, homologous genes for NlFmd have also been identified in two rice planthopper species, the white-backed planthopper (WBPH, Sogotalla furcifera) and the small brown planthopper (SBPH, Laodelphax striatellus), and these genes appear to be involved in the sex determination cascades for these species. Our data suggest that the sex determination cascade in Delphacidae is conserved.

Characterization of S haplotype in a new self-compatible Brassica rapa cultivar Dahuangyoucai

The most important Brassica species, B. rapa, is naturally self-incompatible. Self-compatible mutants would be useful for dissecting the molecular mechanism of self-incompatibility (SI), a process that promotes outcrossing by recognizing and refusing self-pollens. The S haplotype in a new self-compatible B. rapa cultivar, Dahuangyoucai, was characterized for the first time in this study. Sequence analysis of the S-locus genes, SLG (S-locus glycoprotein), SRK (S-locus receptor kinase) and SCR (S-locus cysteine-rich protein) revealed that Dahuangyoucai contained S haplotype highly similar to S-f2, a non-functional class I S haplotype identified in another self-compatible B. rapa cultivar, Yellow Sarson. Mutations of MLPK (M-locus protein kinase) and non-transcription of the male determinant, SCR, were observed in this cultivar, which is similar to the situation reported in Yellow Sarson. With respect to the female determinant, SRK, no transcript was detected in Yellow Sarson but two fragments were detected in Dahuangyoucai. One fragment was highly similar to SRK-f2, but the other fragment was different from the signal factors previously identified in the SI reaction. The results suggest that Dahuangyoucai and Yellow Sarson have the same origin and a similar mechanism of self-compatibility, but diverge after mutations in SRK, SCR and MLPK. Further studying the self-compatibility of Dahuangyoucai might identify novel factors involved in the SI signalling cascade and provide new insights into the mechanisms of SI in Brassicaceae.

Geographical variation in house-fly (Musca domestica L.) sex determinants within the British Isles

SummaryGenetic and cytological analyses of house-flies collected from 12 pig-breeding farms throughout the British Isles demonstrated that the non-standard sex determination mechanism prevailing in South-East England, involving a dominant female determinant (F) and virtual homozygosity for a male determinant on the X chromosome (Xm, both males and females morphologically XX), was not typical of the country as a whole. Instead there was a gradual decrease in the frequency of F, Xm and a rarer male determinant M III, and a concomitant increase in the standard male determining Y chromosome, on moving north, east and west of this region. Only the Scottish and probably the Irish populations were fully standard (XX females XY males), although one from the East Anglian coast in which non-standard determinants were rare was predominantly of this type. Populations from intermediate areas possessed complex multifactorial mechanisms in which Y, F Xm and M III coexisted. It is hypothesized that this radial cline in sex determinants, like the latitudinal cline known from mainland Europe, represents a transient polymorphism caused by the recent and continuing invasion of non-standard determinants into originally standard populations. The cause(s) of this apparently rapid evolutionary change, however, remain unclear.

Identification of a male determinant on the X chromosome of housefly (Musca domestica L.) populations in South-East England

SUMMARYHouseflies collected from eight pig-breeding farms were used to investigate the nature of sex determinants in fly populations of South-East England. Earlier observations had shown that their sex determination mechanism was not of the standard (XX females, XY males) type.Most flies of both sexes were XX; the male determining Y chromosome of standard populations was rare. Test-crosses to females of standard multimarked strains and crosses using aneuploid (OX) flies identified two dominant male determinants, one on autosome 3 (M III) and another on the X chromosome (Xm), and provided the first demonstration in this species of an active involvement of the X chromosome in sex determination. A small secondary constriction on X appeared to indicate reliably the presence of Xm. Most individuals in field populations were Xm homozygotes, implying the presence of an unlocated female determinant F,† epistatic to Xm and M III.M III was less common and differed in frequency between samples. Its increased frequency in a strain selected in the laboratory with the pyrethroid insecticide permethrin might be due either to genetic drift, or to linkage between M III and a gene on autosome 3 that confers resistance to pyrethroids in houseflies.

Intersexuality in Lymantria dispar (L.). A reassessment

R. Goldschmidt worked on intersexuality in the Lepidoptera for many years up to 1934 and the moth Lymantria dispar was his chief experi­mental material. According to him, an intersexual insect develops for a time as one sex and then changes to the other, though the chromosomal sex remains that of the original zygote. If the change takes place early enough in development, e. g. at the formation of the gonads, the whole insect appears to be sexually converted, whereas, if it occurs later, only those structures formed towards the end of development, e. g. the wings, will be affected. Goldschmidt held that, within races, a fixed dosage of female determinant, carried maternally in the cytoplasm or in the Y chromosome and elaborated into the cytoplasm, outweighs the effect of a single dose of male determinant carried in one X chromosome in the heterogametic sex, here the female. In the homogametic sex the double dose of X chromo­somes is balanced against the single dose of female determinant received from the female parent, and results in a male. Moreover, a certain min­imum excess in either direction is required for normal sex determination. He held that, while the relative values of the sex determinants always conform to this plan, their absolute values may differ from one geographical race to another. Consequently, intersexuality due to lack of correct balance between the sex determinants may arise in different ratios when distinct races are crossed. Its degree and type, whether male converted towards female or the reverse, are controlled by the races and sexes used. Since sex abnormalities have appeared, but only sporadically, in more recent genetic work involving race crosses in mimetic butterflies, we decided to reassess Goldschmidt’s results. On repeating those of his crosses that he regarded as the most funda­mental, between German and Japanese material, we bred a number of intersexes, but there were marked discrepancies between his and our overall findings. The matter is discussed and it is shown that the accuracy of the Goldschmidt hypothesis can now be tested in much more detail by using the heterochromatin body in the larva as a prospective marker of chromosomal sex in the adult.