Traumatic epiphysiolysis of the proximal femur

PURPOSE OF THE STUDY

Several former studies show the treatment of slipped epiphysis of the femoral head (SEFH). Its reason is rather unknown. On the other hand the rare traumatic SEFH takes place due to a real accident. According to the literature these injuries are treated like chronic SEFHs. The aim of this study is to show the differences in pathology and treatment of an acute traumatic SEFH in relationship to the chronic SEFH.

PATIENTS AND METHODS

In 8 patients dislocated traumatic SEFHs were reduced anatomically and stabilized by the means of 3 to 4 Kirschner- (K-) wires or two cancellous screws. Each patient got a plaster-cast fixation for about 6 weeks of the ipsilateral hip and leg and was mobilized with two crutches and partial weight bearing for 12 weeks. The implants were removed 24 weeks after surgery. Four patients with not dislocated SEFHs were immobilized or mobilized with two crutches without weight bearing according to their pain sensation. The final examination of both groups took place 2 Vz to 15 years after the initial treatment.

RESULTS

Four patients primarily under 10 years of age showed no or minimal radiological signs of a dislocated femoral head and were without any further inconvenience--the suspected SEFHs revealed as hip contusions. 8 children aged 10 years or older at the time of trauma were treated by closed reduction and internal fixation. Complications occurred in three cases--one necrosis of the femoral head because of a perforating K-wire, one subtrochanteric femur fracture after implant removal of a prophylactically stabilized contralateral femoral head and one minimally dislocated femoral head after postoperative too early full weight bearing.

DISCUSSION

The traumatic SEFH is very different to the chronic one regarding the pathology and acute treatment. Technical challenges must be solved. Unilateral K-wiring or screwing for 24 weeks and reduced weight bearing for the first 12 weeks after surgery is a sufficient way of treatment of the traumatic SEFH.

CONCLUSIONS

In the case of a traumatic SEFH it needs to be reduced anatomically and stabilized by surgical means in the acute phase. A prophylactic stabilization of the opposite intact side is usually not required.

A 5'-uridine amplifies miRNA/miRNA* asymmetry in Drosophila by promoting RNA-induced silencing complex formation

Background

MicroRNA (miRNA) are diverse in sequence and have a single known sequence bias: they tend to start with uridine (U).

Results

Our analyses of fly, worm and mouse miRNA sequence data reveal that the 5′-U is recognized after miRNA production. Only one of the two strands can be assembled into Argonaute protein from a single miRNA/miRNA* molecule: in fly embryo lysate, a 5′-U promotes miRNA loading while decreasing the loading of the miRNA*.

Conclusion

We suggest that recognition of the 5′-U enhances Argonaute loading by a mechanism distinct from its contribution to weakening base pairing at the 5′-end of the prospective miRNA and, as recently proposed in Arabidopsis and in humans, that it improves miRNA precision by excluding incorrectly processed molecules bearing other 5′-nt.

DNA damage by low-energy electron impact: dependence on guanine content

Single-stranded DNA oligonucleotides (33-mers) containing different numbers of guanines (n=1-4) were tethered to a gold surface and exposed to 1 eV electrons. The electrons induced DNA damage, which was analyzed with fluorescence and infrared spectroscopy methods. The damage was identified as strand breaks and found to correlate linearly with the number of guanines in the sequence. This sequence dependence indicates that the electron capture by the DNA bases plays an important role in the damage reaction mechanism.

Sorting of Drosophila small silencing RNAs partitions microRNA* strands into the RNA interference pathway

In flies, small silencing RNAs are sorted between Argonaute1 (Ago1), the central protein component of the microRNA (miRNA) pathway, and Argonaute2 (Ago2), which mediates RNA interference. Extensive double-stranded character-as is found in small interfering RNAs (siRNAs)-directs duplexes into Ago2, whereas central mismatches, like those found in miRNA/miRNA* duplexes, direct duplexes into Ago1. Central to this sorting decision is the affinity of the small RNA duplex for the Dcr-2/R2D2 heterodimer, which loads small RNAs into Ago2. Here, we show that while most Drosophila miRNAs are bound to Ago1, miRNA* strands accumulate bound to Ago2. Like siRNA loading, efficient loading of miRNA* strands in Ago2 favors duplexes with a paired central region and requires both Dcr-2 and R2D2. Those miRNA and miRNA* sequences bound to Ago2, like siRNAs diced in vivo from long double-stranded RNA, typically begin with cytidine, whereas Ago1-bound miRNA and miRNA* disproportionately begin with uridine. Consequently, some pre-miRNA generate two or more isoforms from the same side of the stem that differentially partition between Ago1 and Ago2. Our findings provide the first genome-wide test for the idea that Drosophila small RNAs are sorted between Ago1 and Ago2 according to their duplex structure and the identity of their first nucleotide.

Structural determinants of miRNAs for RISC loading and slicer-independent unwinding

MicroRNAs (miRNAs) regulate expression of their target mRNAs through the RNA-induced silencing complex (RISC), which contains an Argonaute (Ago) family protein as a core component. In Drosophila melanogaster, miRNAs are generally sorted into Ago1-containing RISC (Ago1-RISC). We established a native gel system that can biochemically dissect the Ago1-RISC assembly pathway. We found that miRNA-miRNA* duplexes are loaded into Ago1 as double-stranded RNAs in an ATP-dependent fashion. In contrast, unexpectedly, unwinding of miRNA-miRNA* duplexes is a passive process that does not require ATP or slicer activity of Ago1. Central mismatches direct miRNA-miRNA* duplexes into pre-Ago1-RISC, whereas mismatches in the seed or guide strand positions 12-15 promote conversion of pre-Ago1-RISC into mature Ago1-RISC. Our findings show that unwinding of miRNAs is a precise mirror-image process of target recognition, and both processes reflect the unique geometry of RNAs in Ago proteins.

Collapse of germline piRNAs in the absence of Argonaute3 reveals somatic piRNAs in flies

Piwi-interacting RNAs (piRNAs) silence transposons in animal germ cells. piRNAs are thought to derive from long transcripts spanning transposon-rich genomic loci and to direct an autoamplification loop in which an antisense piRNA, bound to Aubergine or Piwi protein, triggers production of a sense piRNA bound to the PIWI protein Argonaute3 (Ago3). In turn, the new piRNA is envisioned to produce a second antisense piRNA. Here, we describe strong loss-of-function mutations in ago3, allowing a direct genetic test of this model. We find that Ago3 acts to amplify piRNA pools and to enforce on them an antisense bias, increasing the number of piRNAs that can act to silence transposons. We also detect a second, Ago3-independent piRNA pathway centered on Piwi. Transposons targeted by this second pathway often reside in the flamenco locus, which is expressed in somatic ovarian follicle cells, suggesting a role for piRNAs beyond the germline.

Redefining microRNA targets

Animal microRNAs (miRNAs) guide proteins to repress the translation of target mRNAs via imperfect base pairing between the miRNA and the target. Computational analyses suggest that each miRNA regulates tens or hundreds of targets [1, 2], yet genetic studies usually show that the repression of a few targets plays a physiological role [3-5]. The extent of miRNA-mediated repression (which rarely exceeds 2-fold [1, 2]) is also surprisingly lower than most well-tolerated, intrinsic variations in gene expression [6, 7]. Although miRNA targets are well conserved among closely related species, they differ greatly between more distant animals [8]. The prevailing view is that miRNAs "tune" expression of most of their targets [1, 2]. Here, I propose an alternative hypothesis that could resolve these three paradoxes: many computationally identified miRNA targets may actually be competitive inhibitors of miRNA function, preventing miRNAs from binding their authentic targets by sequestering them. Depending on the prevalence of this type of miRNA:mRNA interaction, this new conception of miRNA regulation could have profound implications on our assumptions about miRNA function.

Argonaute loading improves the 5' precision of both MicroRNAs and their miRNA* strands in flies

MicroRNAs (miRNAs) are short regulatory RNAs that direct repression of their mRNA targets. The miRNA "seed"-nucleotides 2-7-establishes target specificity by mediating target binding. Accurate processing of the miRNA 5' end is thought to be under strong selective pressure because a shift by just one nucleotide in the 5' end of a miRNA alters its seed sequence, redefining its repertoire of targets (Figure 1). Animal miRNAs are produced by the sequential cleavage of partially double-stranded precursors by the RNase III endonucleases Drosha and Dicer, thereby generating a transitory double-stranded intermediate comprising the miRNA paired to its partially complementary miRNA* strand. Here, we report that in flies, the 5' ends of miRNAs and miRNA* strands are typically more precisely defined than their 3' ends. Surprisingly, the precision of the 5' ends of both miRNA and miRNA* sequences increases after Argonaute2 (Ago2) loading. Our data imply that either many miRNA* sequences are under evolutionary pressure to maintain their seed sequences-that is, they have targets-or that secondary constraints, such as the sequence requirements for loading small RNAs into functional Argonaute complexes, narrow the range of miRNA and miRNA 5' ends that accumulate in flies.

Endogenous siRNAs derived from transposons and mRNAs in Drosophila somatic cells

Small interfering RNAs (siRNAs) direct RNA interference (RNAi) in eukaryotes. In flies, somatic cells produce siRNAs from exogenous double-stranded RNA (dsRNA) as a defense against viral infection. We identified endogenous siRNAs (endo-siRNAs), 21 nucleotides in length, that correspond to transposons and heterochromatic sequences in the somatic cells of Drosophila melanogaster. We also detected endo-siRNAs complementary to messenger RNAs (mRNAs); these siRNAs disproportionately mapped to the complementary regions of overlapping mRNAs predicted to form double-stranded RNA in vivo. Normal accumulation of somatic endo-siRNAs requires the siRNA-generating ribonuclease Dicer-2 and the RNAi effector protein Argonaute2 (Ago2). We propose that endo-siRNAs generated by the fly RNAi pathway silence selfish genetic elements in the soma, much as Piwi-interacting RNAs do in the germ line.

Rethinking the microprocessor

MicroRNAs (miRNAs) are tiny regulators of gene expression that are processed from longer primary transcripts. In this issue, Han et al. (2006) report some of the structural features of the primary transcript that ensure that the Drosha-DGCR8 enzyme complex liberates precisely the correct precursor sequence, enabling production of a fully functional miRNA.