BackgroundA novel sarcomeric myosin heavy chain gene, MYH14, was identified following the completion of the human genome project. MYH14 contains an intronic microRNA, miR-499, which is expressed in a slow/cardiac muscle specific manner along with its host gene; it plays a key role in muscle fiber-type specification in mammals. Interestingly, teleost fish genomes contain multiple MYH14 and miR-499 paralogs. However, the evolutionary history of MYH14 and miR-499 has not been studied in detail. In the present study, we identified MYH14/miR-499 loci on various teleost fish genomes and examined their evolutionary history by sequence and expression analyses.ResultsSynteny and phylogenetic analyses depict the evolutionary history of MYH14/miR-499 loci where teleost specific duplication and several subsequent rounds of species-specific gene loss events took place. Interestingly, miR-499 was not located in the MYH14 introns of certain teleost fish. An MYH14 paralog, lacking miR-499, exhibited an accelerated rate of evolution compared with those containing miR-499, suggesting a putative functional relationship between MYH14 and miR-499. In medaka, Oryzias latipes, miR-499 is present where MYH14 is completely absent in the genome. Furthermore, by using in situ hybridization and small RNA sequencing, miR-499 was expressed in the notochord at the medaka embryonic stage and slow/cardiac muscle at the larval and adult stages. Comparing the flanking sequences of MYH14/miR-499 loci between torafugu Takifugu rubripes, zebrafish Danio rerio, and medaka revealed some highly conserved regions, suggesting that cis-regulatory elements have been functionally conserved in medaka miR-499 despite the loss of its host gene.ConclusionsThis study reveals the evolutionary history of the MYH14/miRNA-499 locus in teleost fish, indicating divergent distribution and expression of MYH14 and miR-499 genes in different teleost fish lineages. We also found that medaka miR-499 was even expressed in the absence of its host gene. To our knowledge, this is the first report that shows the conversion of intronic into non-intronic miRNA during the evolution of a teleost fish lineage.

Macrobrachium dayanum (Hall) is the second largest freshwater prawn found abundantly in Bangladesh, India and Pakistan in rivers. It is a boneless, tasty and lucrative food item. Very few works are available on the fecundity, metamorphosis and hatching of M. dayanum (Jalihall and Sankoli 1975, Katre andPandian 1972). This lead to the present study.A total of 100 specimens of M. dayanum were collected from the river Padma in Rajshahi during the period from May to July, 2006. After collection, the specimens were washed, sexed and preserved in 5% formalin solution in separate jars in the Fisheries Research Laboratory, Department of Zoology, University of Rajshahi. For counting the eggs, actual counting method was followed. The total length was measured with the help of a measuring board fitted with a meter scale. The weights of the specimens were taken with the help of an electronic balance. Total length (TL) of the specimens was taken by putting it on the measuring board horizontally, fixing its snout tip to zero cm then the measurement was taken up to its tail tip nearer to one cm. For weight measurement electric balance was used. For establishing the relationship between fecundity with total length and total weight, the following formulae were followed: Y = a + b X, where, Y = Fecundity, X = Total length (TL) and, F = a +b TW, where, F=Fecundity, TW= Total weight .

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