A SUMO-dependent regulatory switch connects the piRNA pathway to the heterochromatin machinery in Drosophila

Nuclear Argonaute proteins, guided by small RNAs, mediate sequence-specific heterochromatin formation. The molecular principles that link Argonaute-small RNA complexes to cellular heterochromatin effectors upon binding to nascent target RNAs are poorly understood. Here, we elucidate the mechanism by which the PIWI interacting RNA (piRNA) pathway connects to the heterochromatin machinery in Drosophila. Piwi-mediated stabilization of the corepressor complex SFiNX on chromatin leads to SUMOylation of its subunit Panoramix. SUMOylation, together with an amphipathic LxxLL motif in Panoramix's intrinsically disordered repressor domain, are necessary and sufficient to recruit small ovary (Sov), a multi-zinc finger protein essential for general heterochromatin formation and viability. Structure-guided mutations that abrogate the Panoramix-Sov interaction or that prevent SUMOylation of Panoramix uncouple Sov from the piRNA pathway, resulting in viable but sterile flies in which Piwi-targeted transposons are derepressed. Thus, by coupling recruitment of a corepressor to nascent transcripts with its SUMOylation, Piwi engages the heterochromatin machinery specifically at transposon loci.

A new genus of polystomatid parasitic flatworm (Monogenea: Polystomatidae) without free-swimming life stage from the Malagasy poison frogs

Madapolystoma n. g. (Monogenea, Polystomatidae), is proposed for a new genus of polystomatid from the urinary bladder of the Malagasy poison frogs of the genus Mantella (family Mantellidae), with the description of one new species. This is the second anuran polystome to be described from Madagascar. The parasites are small with a maximum body length of less than 3 mm. The two gut caeca have a few diverticulae but no prehaptoral anastomoses and are confluent posteriorly. The haptor bears six well-developed suckers and one pair of hamuli. A single small ovary lies in mid-body while the single follicular testis lies posteriorly in the body. Vaginae are present. The new genus is unique among all known polystomes in that it apparently has no free-swimming ciliated larvae but instead is characterized by advanced intra-uterine development with larvae developing hamuli and even suckers while still in utero. Based on molecular phylogenetic data, the closest relative of Madapolystoma is the genus Eupolystoma from Africa. Madagascar has a very diverse anuran fauna with a 100% level of endemicity at the species level, and more Madapolystoma species from other mantellid hosts await description.

Drosophila small ovary gene ensures germline stem cell maintenance and differentiation by silencing transposons and organising heterochromatin

Self-renewal and differentiation of stem cells is one of the fundamental biological phenomena relying on proper chromatin organisation. In our study, we describe a novel chromatin regulator encoded by the Drosophila small ovary (sov) gene. We demonstrate that sov is required in both the germline stem cells (GSCs) and the surrounding somatic niche cells to ensure GSC survival and differentiation. Sov maintains niche integrity and function by repressing transposon mobility, not only in the germline, but also in the soma. Protein interactome analysis of Sov revealed a physical interaction between Sov and HP1a. In the germ cell nuclei, Sov co-localises with HP1a, suggesting that Sov affects transposon repression as a component of the heterochromatin. In a position effect variegation assay, we found a dominant genetic interaction between sov and HP1a, indicating their functional cooperation in promoting the spread of heterochromatin. An in vivo tethering assay and FRAP analysis revealed that Sov enhances heterochromatin formation by supporting the recruitment of HP1a to the chromatin. We propose a model in which sov maintains GSC niche integrity by regulating piRNA-mediated transposon silencing as a heterochromatin regulator.Summary statementSmall ovary maintains the integrity of the stem cell niche by regulating piRNA-mediated transposon silencing acting as a key component of the heterochromatin.

Drosophila small ovary encodes a zinc-finger repressor required for ovarian differentiation

Repression is essential for coordinated cell type-specific gene regulation and controlling the expression of transposons. In the Drosophila ovary, stem cell regeneration and differentiation requires controlled gene expression, with derepression leading to tissue degeneration and ovarian tumors. Likewise, the ovary is acutely sensitive to deleterious consequences of transposon derepression. The small ovary (sov) locus was identified in a female sterile screen, and mutants show dramatic ovarian morphogenesis defects. We mapped the locus to the uncharacterized gene CG14438, which encodes a zinc-finger protein that colocalizes with the essential Heterochromatin Protein 1 (HP1a). We demonstrate that Sov functions to repress inappropriate cell signaling, silence transposons, and suppress position-effect variegation in the eye, suggesting a central role in heterochromatin stabilization.

Genetic characterization of small ovaries, a gene required in the soma for the development of the Drosophila ovary and the female germline.

The small ovary gene (sov) is required for the development of the Drosophila ovary. Six EMS-induced recessive alleles have been identified. Hypomorphic alleles are female sterile and have no effect on male fertility, whereas more severe mutations result in lethality. The female-sterile alleles produce a range of mutant phenotypes that affect the differentiation of both somatic and germline tissues. These mutations generally produce small ovaries that contain few egg cysts and disorganized ovarioles, and in the most extreme case no ovarian tissue is present. The mutant egg cysts that develop have aberrant morphology, including abnormal numbers of nurse cells and patches of necrotic cells. We demonstrate that sov gene expression is not required in the germline for the development of functional egg cysts. This indicates that the sov function is somatic dependent. We present evidence using loss-of-function and constitutive forms of the somatic sex regulatory genes that sov activity is essential for the development of the somatic ovary regardless of the chromosomal sex of the fly. In addition, the genetic mapping of the sov locus is presented, including the characterization of two lethal sov alleles and complementation mapping with existing rearrangements.

On the Males and an Intersex-Like Specimen of the Parthenogenetic Saw-Fly Pristiphora Pallipes, LEP

1. Attempts have been made to modify the sex in various species of Tenthredinidæ by immersing leaves holding saw-fly eggs in chemical solutions during maturation which occurs during the first three hours after egg-laying. 2. In Pristiphorapallipes, Lep., which in England appears almost completely thelytokous, it is possible that sex-change has occurred as the result of such treatment for, in five experiments, eggs up to one and a half hours old treated for one hour in a 0.2 per cent, solution of magnesium sulphate (in distilled water) yielded 62 females, 2 males, and 1 intersexlike specimen. 3. Definitive interpretation of these appearances cannot be made until more experimental results are obtained, and more is known of the sex-ratio of the species. The breeding experiments of the writer and Miss E. F. Chawner, in England, involving the rearing of some 600 specimens during eight successive parthenogenetic generations show the male percentage to be between 0.5 per cent, and 1.75 per cent. In Canada Garlick finds it to be 2 per cent, fcom 232 individuals of five successive generations and part of the sixth; larvæ from cultivated bushes yielded 207 ♀ ♀ ; wild larvæ from a wild bush gave 4 per cent.--1 ♂ : 23 ♀ ♀. In South Europe Enslin states that the male is not rare. 4. The external characters of these rare English males and the abnormality, and the external genitalia of one male and the abnormality are described in detail. 5. Externally the abnormality shows the slim build of the male, but has certain female colour characters; its external genitalia comprise a male set, complete except for the genital plate, succeeded by a complete female set of which the two halves of the saw-sheath are smaller than normal, modified in shape and wide apart; the saws and saw-guides lie horizontally instead of sagittally; internally there is a spermatheca and paired gonads leading into normal male ducts ; each gonad to appearance resembles a small ovary with about five follicles, but cytologically they are almost empty except for a few indeterminate cells, a few nurse-cells, and relatively few spermatozoa. 6. This specimen may be either (a) a gynandromorph which genetically is a male with teratological gonads and possessing somatically certain substitutive female characters and arr additive female segment interpolated posteriorly; or (b) a gynandromorph genetically a male with teratological gonads and somatically a female with an additive male genitalring interpolated posteriorly; or (c) an intersex predominantly male (cf. moth intersexes of Goldschmidt, Harrison, and others). 7. Non-disjunction in either a male (X) or female (XX) pallipes egg during segmentation--and preferably during the later stages--could produce the condition of the abnormality. 8. The prime cause to non-disjunction in this almost completely thelytokous species cannot be abnormal intra- or inter-specific fertilisation, but may be hereditary or pathological--both unlikely--or physical or/and chemical disturbance in the relationship between the egg and its nidus in the leaf. Of the latter a possible natural cause is the occasional imperfect deposition of an egg so that a portion of it is exposed to the outer air, but the more likely explanation is the artificial experimental treatment. 9. The simultaneous appearance of two of the extremely rare English males and a unique abnormality from eggs treated as mentioned under (2) strengthen the possibility that these results were artificially produced. It is quite possible that the gonads of the abnormality were not intersexual but teratological, the chemical affecting the germ-tissue in shape only but not in sex. 10. Eight other sexual abnormalites in saw-flies, from other workers' records, are briefly described in their externals principally ; it is tentatively suggested that in the light of recent research they may be classified into two categories, (a) gynandromorphs, (b) intersexes; two of these specimens, Nematinus umbrinus, Zadd., taken wild, may be intersexes resultant upon an inter-specific cross umbrinus x ribesi