29,743 research outputs found
Cytotaxonomy of Antarctic teleosts of the Pagothenia/Trematomus complex (Nototheniidae, Perciformes)
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Heterochromatin of the antarctic ice-fish C. hamatus (Teleostea:Channichthyidae) includes telomeric-like sequences
No full textCytogenetic analysis in Polypterus ornatipinnis (Actinopterygii, Cladistia, Polypteridae) and 5S rDNA
No full textPolypteridae is a family of archaic freshwater African fish that constitute an interesting subject for the study of the karyological evolution in vertebrates, on account of their primitive morphological characters and peculiar relationships with lower Osteichthyans. In this paper, a cytogenetic analysis on twenty specimens of both sexes of Polypterus ornatipinnis the ornate “bichir”, coming from the Congo River basin, was performed by using both classical and molecular techniques. The karyotypic formula (2n = 36; FN = 72) was composed of 26 M + 10 SM. The Alu I banding, performed to characterize heterochromatin in this species, was mainly centromeric. Both the chromosome location of the ribosomal 5S and 18S rRNA genes were examined by using Ag-NOR, classical C-banding, CMA3 staining and FISH. CMA3 marked all centromerical regions and showed the presence of two GC rich regions on the p arm of the chromosome pair n°1 and on the q arm of the pair n°14. Staining with Ag-NOR marked the only telomeric region of the chromosome n°1 p arm. After PCR, the 5S rDNA in this species was cloned, sequenced and analyzed. In the 665 bp 5S rDNA sequence of P.ornatipinnis, a conserved 120 bp gene region for the 5S rDNA was identified, followed by a non-transcribed variable spacer (NTS) which included simple repeats, microsatellites and a fragment of a non-LTR retrotransposon R-TEX. FISH with 5S rDNA marked the subtelomeric region of the q arm of the chromosome pair n°14, previously marked by CMA3. FISH with 18S rDNA marked the telomeric region of the p arm of the pair n°1, previously marked both by Ag-NOR and CMA3. The (GATA)7 repeats marked the telomeric regions of all chromosome pairs, with the exclusion of the n°1, n°3 and n°14; hybridization with telomeric probes (TTAGGG)n showed signals at the end of all chromosomes. Karyotype evolution in Polypterus genus was finally discussed, including the new data obtained
The evolution of networks of innovators within and across borders: Evidence from patent data
No full textRecent studies on the geography of knowledge networks have documented a negative impact of physical distance and institutional borders upon research and development (R&D) collaborations. Though it is widely recognized that geographic constraints and national borders impede the diffusion of knowledge, less attention has been devoted to the temporal evolution of these constraints. In this study we use data on patents filed with the European Patent Office (EPO) for OECD countries to analyze the impact of physical distance and country borders on inter-regional links in four different networks over the period 1988-2009: (1) co-inventorship, (2) patent citations, (3) inventor mobility and (4) the location of R&D laboratories. We find the constraint imposed by country borders and distance decreased until mid-1990s then started to grow, particularly for distance. We further investigate the role of large innovation "hubs" as attractors of new collaboration opportunities and the impact of region size and locality on the evolution of cross-border patenting activities. The intensity of European cross-country
inventor collaborations increased at a higher pace than their non-European counterparts until 2004,
with no significant relative progress thereafter. Moreover, when analyzing networks of geographical mobility, multinational R&D activities and patent citations we cannot detect any substantial progress in European research integration above and beyond the common global trend
Differential DMRT1 expression in the gonads of Podarcis sicula (Reptilia: Lacertidae)
No full textDMRT genes encode a large family of transcription factors which share an unusual cysteine-rich DNA-binding motif, the DM domain. DM family members have been studied in the context of sexual development; in particular, the DMRT1 gene appeared to be the one most directly involved in sex determination, but its activity is largely unexplored and possible downstream targets of this factor have yet to be identified. DMRT1 of the lacertid lizard Podarcis sicula (PsDMRT1) was isolated as a model to study differential gene expression during the seasonal reproductive cycle of an ectothermal species. The adult testis of P. sicula exhibits full activity in spring, complete regression in summer and a slow autumnal recrudescence without spermiation. We cloned a 591-bp partial ORF of the PsDMRT1 fragment, whose putative amino acid sequence contains the conserved DM domain. Northern blot analysis of mRNA from different tissues of P. sicula individuals captured in spring demonstrated DMRT1 transcripts only in testis. Semi-quantitative RT-PCR and in situ hybridization experiments showed peak PsDMRT1 expression in spring, lower expression in autumn and no expression during the period of gonad regression. A possible correlation between androgen level variations and PsDMRT1 transcripts is hypothesized and discussed. Finally, data showed that PsDMRT1 is expressed only in spermatogenic cells, before the second meiotic division, suggesting that its role is confined to the proliferation and maintenance of spermatogonia and spermatocytes
CYTOGENETIC ANALYSIS SHOWS EXTENSIVE GENOMIC REARRANGEMENTS BETWEEN RED HOWLER (ALOUATTA-SENICULUS, LINNAEUS) SUBSPECIES
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