Zebrafish genetics and its implications for understanding vertebrate development

The identification of genes via their mutant phenotypes is the most direct way of dissecting the molecular basis of developmental processes. While this approach has been extremely powerful in invertebrates such as Drosophila and Caenorhabditis elegans, it has until recently been lacking in vertebrates. Now two landmark studies by the groups of Nusslein-Volhard and Driever have for the first time provided the basis for a comprehensive genetic dissection of vertebrate development using the teleost fish, Danio rerio. The mutations identified in these screens look set to revolutionise our understanding of vertebrate development.      

Bupivacaine-induced cellular entry of QX-314 and its contribution to differential nerve block

Background and Purpose: Selective nociceptor fibre block is achieved by introducing the cell membrane impermeant sodium channel blocker lidocaine N-ethyl bromide (QX-314) through transient receptor potential V1 (TRPV1) channels into nociceptors. We screened local anaesthetics for their capacity to activate TRP channels, and characterized the nerve block obtained by combination with QX-314.Experimental Approach: We investigated TRP channel activation in dorsal root ganglion (DRG) neurons by calcium imaging and patch-clamp recordings, and cellular QX-314 uptake by MS. To characterize nerve block, compound action potential (CAP) recordings from isolated nerves and behavioural responses were analysed.Key Results: Of the 12 compounds tested, bupivacaine was the most potent activator of ruthenium red-sensitive calcium entry in DRG neurons and activated heterologously expressed TRPA1 channels. QX-314 permeated through TRPA1 channels and accumulated intracellularly after activation of these channels. Upon sciatic injections, QX-314 markedly prolonged bupivacaine''s nociceptive block and also extended (to a lesser degree) its motor block. Bupivacaine''s blockade of C-, but not A-fibre, CAPs in sciatic nerves was extended by co-application of QX-314. Surprisingly, however, this action was the same in wild-type, TRPA1-knockout and TRPV1/TRPA1-double knockout mice, suggesting a TRP-channel independent entry pathway. Consistent with this, high doses of bupivacaine promoted a non-selective, cellular uptake of QX-314.Conclusions and Implications: Bupivacaine, combined with QX-314, produced a long-lasting sensory nerve block. This did not require QX-314 permeation through TRPA1, although bupivacaine activated these channels. Regardless of entry pathway, the greatly extended duration of block produced by QX-314 and bupivacaine may be clinically useful.     

The distal femoral epiphyseal ossification center in the assessment of third-trimester menstrual age: sonographic identification and measurement

The distal femoral epiphyseal secondary ossification center (DFE), which can be reliably identified and measured sonographically, may assist the sonologist in predicting third-trimester menstrual age. Between 28 and 35 menstrual weeks, the percentage of fetuses with a DFE progressively increases. Although the mean age at DFE appearance is approximately 32-33 menstrual weeks, the DFE may be seen as early as 29 menstrual weeks. Nevertheless, the age of a fetus without an identifiable DFE is most likely less than or equal to 34 menstrual weeks. Measurements of the DFE show that its size increases linearly: the menstrual age of a fetus whose DFE measures greater than or equal to 7mm is most likely greater than or equal to 37 weeks.     

Expression of CDw29 and CD45R antigens on epithelial cells in oral lichen planus

The CD45R and CDw29 antigens are expressed on naive and primed helper T cell populations which serve suppressor-inducer or helper-inducer functions, respectively. These antigens may also be expressed on epithelial cell subpopulations. In the present study, monoclonal antibodies reacting with T lymphocytes and Langerhans cells (LC) were used to characterize the expression of CD45R and CDw29 antigens in oral lichen planus. CDw29 was expressed by LC and lymphocytic cells whereas keratinocyte reactivity varied from negative through to full thickness staining. Expression of CD45R was confined to intraepithelial cells with either lymphocytic or dendritic morphology. A relatively constant ratio of CD1a + LC to CD45R + cells (2:1) was seen. These results demonstrate the existence of intraepithelial cells expressing antigens which are functionally important in T cell responses and which may provide local immunoregulatory influences.     

Nonpalpable breast lesion localization: limited efficacy of sonography

We attempted to use hand-held, high-resolution breast sonography to localize for biopsy 11 solid, nonpalpable lesions detected by mammography. Using sonography, we identified and localized only one of four lesions presenting as poorly defined masses and only one of seven lesions presenting as clusters of tiny calcifications. This 18% rate of success is too low to justify the use of sonography for all patients undergoing needle localization. Mammography remains the procedure of choice for localizing solid, nonpalpable breast masses and clustered calcifications.