The Thoc1 encoded ribonucleoprotein is required for myeloid progenitor cell homeostasis in the adult mouse.

Co-transcriptionally assembled ribonucleoprotein (RNP) complexes are critical for RNA processing and nuclear export. RNPs have been hypothesized to contribute to the regulation of coordinated gene expression, and defects in RNP biogenesis contribute to genome instability and disease. Despite the large number of RNPs and the importance of the molecular processes they mediate, the requirements for individual RNP complexes in mammalian development and tissue homeostasis are not well characterized. THO is an evolutionarily conserved, nuclear RNP complex that physically links nascent transcripts with the nuclear export apparatus. THO is essential for early mouse embryonic development, limiting characterization of the requirements for THO in adult tissues. To address this shortcoming, a mouse strain has been generated allowing inducible deletion of the Thoc1 gene which encodes an essential protein subunit of THO. Bone marrow reconstitution was used to generate mice in which Thoc1 deletion could be induced specifically in the hematopoietic system. We find that granulocyte macrophage progenitors have a cell autonomous requirement for Thoc1 to maintain cell growth and viability. Lymphoid lineages are not detectably affected by Thoc1 loss under the homeostatic conditions tested. Myeloid lineages may be more sensitive to Thoc1 loss due to their relatively high rate of proliferation and turnover.

Identification of an alternate splice form of tapasin in human melanoma.

Assembly of major histocompatibility complex (MHC) class I molecules with peptide in the endoplasmic reticulum requires the assistance of tapasin. Alternative splicing, which is known to regulate many genes, has been reported for tapasin only in the context of mutations. Here, we report on an alternate splice form of tapasin (tpsnΔEx3) derived from a human melanoma cell line that does not appear to be caused by mutations. Excision of exon 3 results in deletion of amino acids 70 to 156 within the beta barrel region, but the membrane proximal Ig domain, the transmembrane domain, and cytoplasmic tail of tapasin are intact. Introduction of tpsnΔEx3 into a tapasin-deficient cell line does not restore MHC class I expression at the cell surface. Similar to a previously described tapasin mutant (tpsnΔN50), tpsnΔEx3 interacts with TAP. Therefore, we used these altered forms of tapasin to test the importance of MHC class I interaction with TAP. In the presence of wild-type tapasin, transfection of tpsnΔN50, but not tpsnΔEx3, reduced MHC class I expression at the cell surface likely due its ability to compete MHC class I molecules from TAP. Together these findings suggest that tumor cells may contain alternate splice forms of tapasin which may regulate MHC class I antigen presentation.

What is the role of alternate splicing in antigen presentation by major histocompatibility complex class I molecules?

The expression of major histocompatibility complex (MHC) class I molecules on the cell surface is critical for recognition by cytotoxic T lymphocytes (CTL). This recognition event leads to destruction of cells displaying MHC class I-viral peptide complexes or cells displaying MHC class I-mutant peptide complexes. Before they can be transported to the cell surface, MHC class I molecules must associate with their peptide ligand in the endoplasmic reticulum (ER) of the cell. Within the ER, numerous proteins assist in the appropriate assembly and folding of MHC class I molecules. These include the heterodimeric transporter associated with antigen processing (TAP1 and TAP2), the heterodimeric chaperone-oxidoreductase complex of tapasin and ERp57 and the general ER chaperones calreticulin and calnexin. Each of these accessory proteins has a well-defined role in antigen presentation by MHC class I molecules. However, alternate splice forms of MHC class I heavy chains, TAP and tapasin, have been reported suggesting additional complexity to the picture of antigen presentation. Here, we review the importance of these different accessory proteins and the progress in our understanding of alternate splicing in antigen presentation.

Preference for venepuncture site: should the patient be consulted?

A questionnaire-based study was undertaken to ascertain if patient preferences were being met in clinical practice by investigating patients' past experience of venepuncture and patient and operator preference for venepuncture site. Patients and operators expressed a preference for either the dorsum of the hand or the antecubital fossa as sites of venous access. Patients who expressed a preference for the dorsum of the hand were more likely to have received venepuncture in their chosen site, although the likelihood of venepuncture failure is higher in the dorsum of the hand than in the antecubital fossa.