Supraspliceosomes at defined functional states portray the pre-assembled nature of the pre-mRNA processing machine in the cell nucleus.

When isolated from mammalian cell nuclei, all nuclear pre-mRNAs are packaged in multi-subunit large ribonucleoprotein complexes-supraspliceosomes-composed of four native spliceosomes interconnected by the pre-mRNA. Supraspliceosomes contain all five spliceosomal U snRNPs, together with other splicing factors, and are functional in splicing. Supraspliceosomes studied thus far represent the steady-state population of nuclear pre-mRNAs that were isolated at different stages of the splicing reaction. To analyze specific splicing complexes, here, we affinity purified Pseudomonas aeruginosa phage 7 (PP7)-tagged splicing complexes assembled in vivo on Adenovirus Major Late (AdML) transcripts at specific functional stages, and characterized them using molecular techniques including mass spectrometry. First, we show that these affinity purified splicing complexes assembled on PP7-tagged AdML mRNA or on PP7-tagged AdML pre-mRNA are assembled in supraspliceosomes. Second, similar to the general population of supraspliceosomes, these defined supraspliceosomes populations are assembled with all five U snRNPs at all splicing stages. This study shows that dynamic changes in base-pairing interactions of U snRNA:U snRNA and U snRNA:pre-mRNA that occur in vivo during the splicing reaction do not require changes in U snRNP composition of the supraspliceosome. Furthermore, there is no need to reassemble a native spliceosome for the splicing of each intron, and rearrangements of the interactions will suffice.

Regeneration of injured articular cartilage using the recombinant human amelogenin protein.

Aims: Cartilage injuries rarely heal spontaneously and often require surgical intervention, leading to the formation of biomechanically inferior fibrous tissue. This study aimed to evaluate the possible effect of amelogenin on the healing process of a large osteochondral injury (OCI) in a rat model. Methods: A reproducible large OCI was created in the right leg femoral trochlea of 93 rats. The OCIs were treated with 0.1, 0.5, 1.0, 2.5, or 5.0 µg/µl recombinant human amelogenin protein (rHAM+) dissolved in propylene glycol alginate (PGA) carrier, or with PGA carrier alone. The degree of healing was evaluated 12 weeks after treatment by morphometric analysis and histological evaluation. Cell recruitment to the site of injury as well as the origin of the migrating cells were assessed four days after treatment with 0.5 µg/µl rHAM+ using immunohistochemistry and immunofluorescence. Results: A total of 12 weeks after treatment, 0.5 µg/µl rHAM+ brought about significant repair of the subchondral bone and cartilage. Increased expression of proteoglycan and type II collagen and decreased expression of type I collagen were revealed at the surface of the defect, and an elevated level of type X collagen at the newly developed tide mark region. Conversely, the control group showed osteoarthritic alterations. Recruitment of cells expressing the mesenchymal stem cell (MSC) markers CD105 and STRO-1, from adjacent bone marrow toward the OCI, was noted four days after treatment. Conclusion: We found that 0.5 µg/µl rHAM+ induced in vivo healing of injured articular cartilage and subchondral bone in a rat model, preventing the destructive post-traumatic osteoarthritic changes seen in control OCIs, through paracrine recruitment of cells a few days after treatment.

Regeneration of grade 3 ankle sprain, using the recombinant human amelogenin protein (rHAM+ ) in a rat model.

Lateral ligament tears, also known as high-grade ankle sprains, are common, debilitating, and usually heal slowly. Ten to thirty percent of patients continue to suffer from chronic pain and ankle instability even after 3 to 9 months. Previously, we showed that the recombinant human amelogenin (rHAM+ ) induced regeneration of fully transected rat medial collateral ligament, a common proof-of-concept model. Our aim was to evaluate whether rHAM+ can regenerate torn ankle calcaneofibular ligament (CFL), an important component of the lateral ankle stabilizers. Right CFLs of Sabra rats were transected and treated with 0, 0.5, or 1 µg/µL rHAM+ dissolved in propylene glycol alginate (PGA). Results were compared with the normal group, without surgery. Healing was evaluated 12 weeks after treatment by mechanical testing (ratio between the right and left, untransected ligaments of the same rat), and histology including immunohistochemical staining of collagen I and S100. The mechanical properties, structure, and composition of transected ligaments treated with 0.5 µg/µL rHAM+ (experimental) were similar to untransected ligaments. PGA (control) treated ligaments were much weaker, lax, and unorganized compared with untransected ligaments. Treatment with 1 µg/µL rHAM+ was not as efficient as 0.5 µg/µL rHAM+ . Normal arrangement of collagen I fibers and of proprioceptive nerve endings, parallel to the direction of the force, was detected in ligaments treated with 0.5 µg/µL rHAM+ , and scattered arrangement, resembling scar tissue, in control ligaments. In conclusion, we showed that rHAM+ induced significant mechanical and structural regeneration of torn rat CFLs, which might be translated into treatment for grades 2 and 3 ankle sprain injuries.