Obligatory parthenogenesis and TE load: Bacillus stick insects and the R2 non-LTR retrotransposon

Comparative Proteomic Analysis Provides New Insights into the Molecular Basis of Thermal-Induced Parthenogenesis in Silkworm (Bombyx mori)

Artificial parthenogenetic induction via thermal stimuli in silkworm is an important technique that has been used in sericultural production. However, the molecular mechanism underlying it remains largely unknown. We have created a fully parthenogenetic line (PL) with more than 85% occurrence and 80% hatching rate via hot water treatment and genetic selection, while the parent amphigenetic line (AL) has less than 30% pigmentation rate and less than 1% hatching rate when undergoing the same treatment. Here, isobaric tags for relative and absolute quantitation (iTRAQ)-based analysis were used to investigate the key proteins and pathways associated with silkworm parthenogenesis. We uncovered the unique proteomic features of unfertilized eggs in PL. In total, 274 increased abundance proteins and 211 decreased abundance proteins were identified relative to AL before thermal induction. Function analysis displayed an increased level of translation and metabolism in PL. After thermal induction, 97 increased abundance proteins and 187 decreased abundance proteins were identified. An increase in stress response-related proteins and decrease in energy metabolism suggested that PL has a more effective response to buffer the thermal stress than AL. Cell cycle-related proteins, including histones, and spindle-related proteins were decreased in PL, indicating an important role of this decrease in the process of ameiotic parthenogenesis.

High Prevalence and Disease Correlation of Autoantibodies Against p40 Encoded by Long Interspersed Nuclear Elements in Systemic Lupus Erythematosus

OBJECTIVE

Long interspersed nuclear element 1 (LINE-1) encodes 2 proteins, the RNA binding protein p40 and endonuclease and reverse transcriptase (open-reading frame 2p [ORF2p]), which are both required for LINE-1 to retrotranspose. In cells expressing LINE-1, these proteins assemble with LINE-1 RNA and additional RNA binding proteins, some of which are well-known autoantigens in patients with systemic lupus erythematosus (SLE). This study was undertaken to investigate whether SLE patients also produce autoantibodies against LINE-1 p40.

METHODS

Highly purified p40 protein was used to quantitate IgG autoantibodies in serum from 172 SLE patients and from disease controls and age-matched healthy subjects by immunoblotting and enzyme-linked immunosorbent assay (ELISA). Preparations of p40 that also contained associated proteins were analyzed by immunoblotting with patient sera.

RESULTS

Antibodies reactive with p40 were detected in the majority of patients and many healthy controls. Their levels were higher in patients with SLE, but not those with systemic sclerosis, compared to healthy subjects (P = 0.01). Anti-p40 reactivity was higher in patients during a flare than in patients with disease in remission (P = 0.03); correlated with the SLE Disease Activity Index score (P = 0.0002), type I interferon score (P = 0.006), decrease in complement C3 level (P = 0.0001), the presence of anti-DNA antibodies (P < 0.0001) and anti-C1q antibodies (P = 0.004), and current or past history of nephritis (P = 0.02 and P = 0.003, respectively); and correlated inversely with age (r = -0.49, P < 0.0001). SLE patient sera also reacted with p40-associated proteins.

CONCLUSION

Autoantibodies reacting with LINE-1 p40 characterize a population of SLE patients with severe and active disease. These autoantibodies may represent an early immune response against LINE-1 p40 that does not yet by itself imply clinically significant autoimmunity, but may represent an early, and still reversible, step toward SLE pathogenesis.

Hybridogenesis and a potential case of R2 non-LTR retrotransposon horizontal transmission in Bacillus stick insects (Insecta Phasmida)

Horizontal transfer (HT) is an event in which the genetic material is transferred from one species to another, even if distantly related, and it has been demonstrated as a possible essential part of the lifecycle of transposable elements (TEs). However, previous studies on the non-LTR R2 retrotransposon, a metazoan-wide distributed element, indicated its vertical transmission since the Radiata-Bilateria split. Here we present the first possible instances of R2 HT in stick insects of the genus Bacillus (Phasmida). Six R2 elements were characterized in the strictly bisexual subspecies B. grandii grandii, B. grandii benazzii and B. grandii maretimi and in the obligatory parthenogenetic taxon B. atticus. These elements were compared with those previously retrieved in the facultative parthenogenetic species B. rossius. Phylogenetic inconsistencies between element and host taxa, and age versus divergence analyses agree and support at least two HT events. These HT events can be explained by taking into consideration the complex Bacillus reproductive biology, which includes also hybridogenesis, gynogenesis and androgenesis. Through these non-canonical reproductive modes, R2 elements may have been transferred between Bacillus genomes. Our data suggest, therefore, a possible role of hybridization for TEs survival and the consequent reshaping of involved genomes.