RESUMEN
Vertebrates evolved an endothelium-lined hemostatic system and a pump-driven pressurized circulation with a finely-balanced coagulation cascade and elaborate blood pressure control over the past 500 million years. Genome analyses have identified principal components of the ancestral coagulation system, however, how this complex trait was originally regulated is largely unknown. Likewise, little is known about the roots of blood pressure control in vertebrates. Here we studied three members of the serpin superfamily that interfere with procoagulant activity and blood pressure of lampreys, a group of basal vertebrates. Angiotensinogen from these jawless fish was found to fulfill a dual role by operating as a highly selective thrombin inhibitor that is activated by heparin-related glycosaminoglycans, and concurrently by serving as source of effector peptides that activate type 1 angiotensin receptors. Lampreys, uniquely among vertebrates, thus use angiotensinogen for interference with both coagulation and osmo- and pressure regulation. Heparin cofactor II from lampreys, in contrast to its paralogue angiotensinogen, is preferentially activated by dermatan sulfate, suggesting that these two serpins affect different facets of thrombin's multiple roles. Lampreys also express a lineage-specific serpin with anti-factor Xa activity, which demonstrates that another important procoagulant enzyme is under inhibitory control. Comparative genomics suggests that orthologues of these three serpins were key components of the ancestral hemostatic system. It appears that, early in vertebrate evolution, coagulation and osmo- and pressure regulation crosstalked through antiproteolytically active angiotensinogen, a feature that was lost during vertebrate radiation, though in gnathostomes interplay between these traits is effective.
Asunto(s)
Evolución Biológica , Coagulación Sanguínea/fisiología , Presión Sanguínea/fisiología , Lampreas/fisiología , Serpinas/metabolismo , Angiotensinógeno/metabolismo , Animales , Secuencia de Bases , Biología Computacional , Cartilla de ADN/genética , ADN Complementario/genética , Glicosaminoglicanos/metabolismo , Cofactor II de Heparina/genética , Cofactor II de Heparina/metabolismo , Microscopía Confocal , Modelos Biológicos , Datos de Secuencia Molecular , Mutagénesis Sitio-Dirigida , Receptor de Angiotensina Tipo 1/genética , Receptor de Angiotensina Tipo 1/metabolismo , Análisis de Secuencia de ADNRESUMEN
BACKGROUND: Intron gains reportedly are very rare during evolution of vertebrates, and the mechanisms underlying their creation are largely unknown. Previous investigations have shown that, during metazoan radiation, the exon-intron patterns of serpin superfamily genes were subject to massive changes, in contrast to many other genes. RESULTS: Here we investigated intron dynamics in the serpin superfamily in lineages pre- and postdating the split of vertebrates. Multiple intron gains were detected in a group of ray-finned fishes, once the canonical groups of vertebrate serpins had been established. In two genes, co-occurrence of non-standard introns was observed, implying that intron gains in vertebrates may even happen concomitantly or in a rapidly consecutive manner. DNA breakage/repair processes associated with genome compaction are introduced as a novel factor potentially favoring intron gain, since all non-canonical introns were found in a lineage of ray-finned fishes that experienced genomic downsizing. CONCLUSION: Multiple intron acquisitions were identified in serpin genes of a lineage of ray-finned fishes, but not in any other vertebrates, suggesting that insertion rates for introns may be episodically increased. The co-occurrence of non-standard introns within the same gene discloses the possibility that introns may be gained simultaneously. The sequences flanking the intron insertion points correspond to the proto-splice site consensus sequence MAG upward arrowN, previously proposed to serve as intron insertion site. The association of intron gains in the serpin superfamily with a group of fishes that underwent genome compaction may indicate that DNA breakage/repair processes might foster intron birth.
Asunto(s)
Intrones , Serpinas/genética , Empalmosomas/genética , Secuencia de Aminoácidos , Angiotensinógeno/genética , Animales , Peces/genética , Datos de Secuencia Molecular , Alineación de Secuencia , Vertebrados/genéticaRESUMEN
By applying homology-search and text-mining programs we have found that the Drosophila serine protease inhibitor (serpin) gene sp4 harbours four reactive centre-coding exons. The mutually exclusive use of these cassettes in combination with alternatively selectable exons at the 5'-end or in the 3'-untranslated region of the gene allows generation of more than ten different transcripts, all of which are expressed in Drosophila embryos. These transcripts may code for eight different Sp4 protein isoforms with different biological functions, which - dependent on the splice pattern - either may be secreted, reside in the endoplasmic reticulum, or may be located in the cytoplasm. An examination revealed the presence of two serpin genes, each coding for two or three likely alternative reactive centre exon cassettes, respectively, also in the Caenorhabditis elegans genome. The occurrence of such serpin genes in some groups of metazoa reflects a parsimonious way to enlarge the adaptive ability of these organisms to cope with a plethora of different serine and cysteine proteases.