A novel isoform of myosin alkali light chain isolated from human muscle cells

Identification of genes expressed in the Xenopus inner ear

Recent studies indicate that hearing loss in humans has strong hereditary components associated with expression of specific genes in the auditory apparatus of the inner ear. However, the inner ear poses challenges for molecular research because the amount of tissue that can be isolated is limited, and extraction procedures yield small quantities of RNA and protein. To begin to identity genes essential for auditory function, we synthesized a cDNA library using an RT-PCR protocol and total RNA isolated from eight Xenopus laevis inner ears. Sequence analysis of randomly selected clones demonstrated expression of both identified (calmodulin, SNARE protein, syndecan-2) and unidentified genes, and confirmed synthesis of full length transcripts. Confocal and scanning electron microscopy (SEM) were used to examine the structure of inner ear organs that serve as auditory receptors in amphibians: the sacculus, the amphibian papilla and the basilar papilla. SEM images illustrate the heterogeneity of bundle morphology and demonstrate the continuous appearance of stereociliary bundles in the X. laevis amphibian papilla during larval development and adult life. Investigations of gene expression in Xenopus auditory organs using clones recovered from inner ear cDNA libraries should provide insight regarding the molecular basis of hearing.

Minor-myosin, a novel myosin isoform synthesized preferentially in Drosophila testis is encoded by the muscle myosin heavy chain gene

Searching for structural proteins involved in spermatogenesis of Drosophila, we found a novel myosin isoform in the testis of Drosophila hydei and D. melanogaster. The transcript encoding this isoform, which we called 'minor-myosin', initiates within the intron between exons 12 and 13 of the muscle myosin heavy chain (mMHC) gene. Minor-myosin contains a common myosin tail but no ordinary myosin head domain. Instead, it has a short N-terminal domain which displays similarity with the N-termini of certain myosin light chain proteins. Western blots with male germ line mutants showed that the novel mMHC isoform is synthesized in the male germ cells, mainly postmeiotically. However, minor-myosin is not testis-specific, as it is expressed at a low level in the fly carcasses. The possible functions of the myosin isoform in the male germ line are discussed.

Evolution of EF-hand calcium-modulated proteins. II. Domains of several subfamilies have diverse evolutionary histories

In the first report in this series we described the relationships and evolution of 152 individual proteins of the EF-hand subfamilies. Here we add 66 additional proteins and define eight (CDC, TPNV, CLNB, LPS, DGK, 1F8, VIS, TCBP) new subfamilies and seven (CAL, SQUD, CDPK, EFH5, TPP, LAV, CRGP) new unique proteins, which we assume represent new subfamilies. The main focus of this study is the classification of individual EF-hand domains. Five subfamilies--calmodulin, troponin C, essential light chain, regulatory light chain, CDC31/caltractin--and three uniques--call, squidulin, and calcium-dependent protein kinase--are congruent in that all evolved from a common four-domain precursor. In contrast calpain and sarcoplasmic calcium-binding protein (SARC) each evolved from its own one-domain precursor. The remaining 19 subfamilies and uniques appear to have evolved by translocation and splicing of genes encoding the EF-hand domains that were precursors to the congruent eight and to calpain and to SARC. The rates of evolution of the EF-hand domains are slower following formation of the subfamilies and establishment of their functions. Subfamilies are not readily classified by patterns of calcium coordination, interdomain linker stability, and glycine and proline distribution. There are many homoplasies indicating that similar variants of the EF-hand evolved by independent pathways.

The human embryonic myosin alkali light chain gene: use of alternative promoters and 3' non-coding regions

Recently we have found evidence that the human embryonic myosin alkali light chain (MLC1 emb) gene has two functional promoters and that its mRNAs exhibit heterogeneity in their 3'untranslated regions (UTR). To study this more in detail we have isolated and characterized the human MLC1emb gene. We focussed in particular on 2 kilobases of 5'flanking region and the alternative 3'UTRs. RNA primer extension and S1 mapping analyses revealed that the MLC1emb gene can indeed be driven either by a proximal or a distal promoter, both in fetal and adult cardiac tissue. These MLC1emb RNAs can contain either the proximal or distal 3'UTR. In contrast to this, in fetal as well as adult masseter muscle MLC1emb mRNA is predominantly transcribed from the proximal promoter and contains mainly the distal 3'UTR. These results explain the known heterogeneity of MLC1emb mRNAs. Finally, we present evidence that the murine MLC1emb gene also contains a functional distal promoter element which has hitherto been undetected.