Empirical evidence of a trade-off between reproductive effort and expectation of future reproduction in female three-spined sticklebacks

Optimal life-history models generally predict that the reproductive effort of iteroparous organisms may increase with age, as their expectation of future reproduction decreases. The population of three-spined sticklebacks (Gasterosteus aculeatus) in the Camargue (Rhone River Delta, France) is annual, all adults dying after their first breeding season. As the three-spined stickleback is a multiple spawner, we tested the hypothesis that reproductive effort may increase during the breeding season on field data. From 1987 to 1998, 653 female sticklebacks were collected in the field during the breeding seasons. The body size, body weight and weights of the liver, gonads and carcass were measured for these individuals. Only gravid females with mature eggs (176 fish) were included in the analysis. Considering the female three-spined stickleback as a capital breeder, the energetic resources available for allocation between soma and gonads were estimated by its body weight. Somatic condition decreased during the breeding season and reproductive effort (gonad weight relative to body weight) increased. These patterns did not vary significantly between years. These observed variations in reproductive effort during the breeding season can be interpreted as empirical evidence of a trade-off between reproductive effort and expectation of future reproduction.     

Polymorphism and signature of selection in the MHC class I genes of the three-spined stickleback Gasterosteus aculeatus

The role and intensity of positive selection maintaining the polymorphism of major histocompatibility complex (MHC) class I genes in the three-spined stickleback Gasterosteus aculeatus was investigated. The highly polymorphic set of MHC class I genes found was organized in a single linkage group. Between 5 and 14 sequence variants per individual were identified by single-stranded conformation polymorphism (SSCP) analysis. Segregation analysis studied in 10 three-spined stickleback families followed the expected pattern of Mendelian inheritance. The gamete fusion in three-spined stickleback thus seems to be random with respect to the MHC class I genes. The DNA sequence analyses showed that the expressed MHC class I loci are under strong selection pressure, possibly mediated by parasites. Codons that were revealed to be under positive selection are potentially important in antigen binding. MHC class I sequences did not form significant supported clusters within a phylogenetic tree. Analogous to MHC class II genes, it was not possible to assign the class I sequences to a specific locus, suggesting that the class I genes may have been generated by recent gene duplication.     

Functional diversity of human protein kinase splice variants marks significant expansion of human kinome

Background

The low pH environment of the human stomach is lethal for most microorganisms; but not Escherichia coli, which can tolerate extreme acid stress. Acid resistance in E. coli is hierarchically controlled by numerous regulators among which are small noncoding RNAs (sncRNA).

Results

In this study, we individually deleted seventy-nine sncRNA genes from the E. coli K12-MG1655 chromosome, and established a single-sncRNA gene knockout library. By systematically screening the sncRNA mutant library, we show that the sncRNA GcvB is a novel regulator of acid resistance in E. coli. We demonstrate that GcvB enhances the ability of E. coli to survive low pH by upregulating the levels of the alternate sigma factor RpoS.

Conclusion

GcvB positively regulates acid resistance by affecting RpoS expression. These data advance our understanding of the sncRNA regulatory network involved in modulating acid resistance in E. coli.     

Comparative Study of the Lateral-line System of the Three-spined Stickleback (Gasterosteus aculeatus) and the Nine-spined Stickleback (Pungitius pungitius)

Abstract The morphology of the lateral-line system of the nine-spined stickleback (Pungitius pungitius) and the three-spined stickleback (Gasterosteus aculeatus) has been studied. In the nine-spined stickleback, a preopercular, infraorbital, supraorbital, postotic and peduncular canal can be identified on both sides of the body. Replacement lines are found as a continuation of the preopercular and infraorbital canal. In addition, lines of free neuromasts are found on the mandible and trunk. An accessory line is present above and below the peduncular canal. The presence of both canals and accessory lines on the peduncle suggests that the peduncle in this species has important sensory functions. No canals are found in the three-spined stickleback. Instead, replacement lines corresponding to the canals can be identified on the head. Accordingly, the lateral-line system of the three-spined and the nine-spined stickleback has a different structure. The lateral-line system of both species shows signs of specialization but the three-spined stickleback has a more specialized lateral-line system than the nine-spined stickleback.     

The fused toes locus is essential for somatic-germ cell interactions that foster germ cell maturation in developing gonads in mice

Ovarian development absolutely depends on communication between somatic and germ cell components. In contrast, it is not until after birth that interactions between somatic and germ cells play an important role in testicular maturation and spermatogenesis. Previously, we discovered that Irx3 expression was localized specifically to female gonads during embryonic development; therefore, we sought to determine the function of this genetic locus in developing gonads of both sexes. The fused toes (Ft) mutant mouse is missing 1.6 Mb of chromosome 8, which includes the entire IrxB cluster (Irx3, Irx5, Irx6), Ftm, Fts, and Fto genes. Homozygote Ft mutant embryos die around embryonic day 13.5 (E13.5); therefore, to assess later development, we harvested gonads at E11.5 and transplanted them into nude mouse hosts. Our results show defects in somatic and germ cell maturation in developing gonads of both sexes. Testis development was normal initially; however, by 3-wk posttransplantation, expression of Sertoli and peritubular myoid cell markers were decreased. In many cases, gonocytes failed to migrate to structurally impaired basement membranes of seminiferous cords. Developmental abnormalities of the ovary appeared earlier and were more severe. Over time, the Ft mutant ovary formed very few primordial or primary follicles, which contained oocytes that failed to grow and were surrounded by scarce granulosa cells that expressed low levels of FOXL2. By 3 wk after transplantation, it was difficult to identify ovarian tissue in Ft mutant ovary transplants. In summary, we conclude that the Ft locus contains genes essential for somatic-germ cell interactions, without which the germ cell niche fails to mature in both sexes.     

Lipid and Fatty Acid Status of the Liver and Gonads of the Three-Spined Stickleback Gasterosteus aculeatus (Gastrosteidae) from Different Spawning Grounds in the White Sea

Biology Bulletin - The content of the total lipids, including structural and storage, and fatty acids (FAs) was evaluated in the liver and gonads of females of the three-spined stickleback...     

Comparison of taste preferences in the three-spined Gasterosteus aculeatus and nine-spined Pungitius pungitius sticklebacks from the White Sea Basin

Similarity between the taste preferences of classical taste substances and free L-amino acids in adult three-spined stickleback Gasterosteus aculeatus (forma leiurus) and nine-spined stickleback Pungitius pungitius (forma laevis) was found. The strongest and the most significant responses in both species were evoked by citric acid and cysteine, asparatic, and glutamic acids. Sodium chloride, calcium chloride, sucrose, and the remaining 18 amino acids do not elicit a statistically significant effect on the consumption of agar-agar pellets by the fish or have weak taste attractiveness. Similarity of taste preferences in the three-spined and nine-spined sticklebacks are supported by correlation analysis. Absolute values of the consumption of pellets of the same types are also similar in the two species. There were, however, differences in the behavioral taste response, repeated snaps, and the duration of processing of the pellets. The taste response of the nine-spined stickleback is more similar to taste responses in fish of the limnophilic complex than to the response in the three-spined stickleback. It is hypothesized that taste spectra may be very similar in fish with similar ecology and feeding patterns not only in sticklebacks, but also in other related species.     

Molecular cloning and characterization of a nuclear androgen receptor activated by 11-ketotestosterone

Although 11-ketotestosterone is a potent androgen and induces male secondary sex characteristics in many teleosts, androgen receptors with high binding affinity for 11-ketotestosterone or preferential activation by 11-ketotestosterone have not been identified. So, the mechanism by which 11-ketotestosterone exhibits such high potency remains unclear. Recently we cloned the cDNA of an 11-ketotestosterone regulated protein, spiggin, from three-spined stickleback renal tissue. As spiggin is the only identified gene product regulated by 11-ketotestosterone, the stickleback kidney is ideal for determination of the mechanism of 11-ketotestosterone gene regulation. A single androgen receptor gene with two splicing variants, belonging to the androgen receptor-β subfamily was cloned from stickleback kidney. A high affinity, saturable, single class of androgen specific binding sites, with the characteristics of an androgen receptor, was identified in renal cytosolic and nuclear fractions. Measurement of ligand binding moieties in the cytosolic and nuclear fractions as well as to the recombinant receptor revealed lower affinity for 11-ketotestosterone than for dihydrotestosterone. Treatment with different androgens did not up-regulate androgen receptor mRNA level or increase receptor abundance, suggesting that auto-regulation is not involved in differential ligand activation. However, comparison of the trans-activation potential of the stickleback androgen receptor with the human androgen receptor, in both human HepG2 cells and zebrafish ZFL cells, revealed preferential activation by 11-ketotestosterone of the stickleback receptor, but not of the human receptor. These findings demonstrate the presence of a receptor preferentially activated by 11-ketotestosterone in the three-spined stickleback, so far the only one known in any animal.     

Cytochrome P450 1A, 1B, and 1C mRNA induction patterns in three-spined stickleback exposed to a transient and a persistent inducer

Cytochrome P450 1 (CYP1) mRNA induction patterns in three-spined stickleback (Gasterosteus aculeatus) were explored for use in environmental monitoring of aryl hydrocarbon receptor (AHR) agonists. The cDNAs of stickleback CYP1A, CYP1B1, CYP1C1, and CYP1C2 were cloned and their basal and induced expression patterns were determined in the brain, gill, liver and kidney. Also, their induction time courses were compared after waterborne exposure to a transient (indigo) or a persistent (3,3',4,4',5-pentacholorbiphenyl PCB 126) AHR agonist. The cloned stickleback CYP1s exhibited a high amino acid sequence identity compared with their zebrafish orthologs and their constitutive tissue distribution patterns largely agreed with those reported in other species. PCB 126 (100 nM) induced different CYP1 expression patterns in the four tissues, suggesting tissue-specific regulation. Both indigo (1 nM) and PCB 126 (10 nM) induced a strong CYP1 expression in gills. However, while PCB 126 gave rise to a high and persistent induction in gills and liver, induction by indigo was transient in both organs. The number of putative dioxin response elements found in each CYP1 gene promoter roughly reflected the induction levels of the genes. The high responsiveness of CYP1A, CYP1B1, and CYP1C1 observed in several organs suggests that three-spined stickleback is suitable for monitoring of pollution with AHR agonists.     

SncRNA715 Inhibits Schwann Cell Myelin Basic Protein Synthesis

Myelin basic proteins (MBP) are major constituents of the myelin sheath in the central nervous system (CNS) and the peripheral nervous system (PNS). In the CNS Mbp translation occurs locally at the axon-glial contact site in a neuronal activity-dependent manner. Recently we identified the small non-coding RNA 715 (sncRNA715) as a key inhibitor of Mbp translation during transport in oligodendrocytes. Mbp mRNA localization in Schwann cells has been observed, but has not been investigated in much detail. Here we could confirm translational repression of Mbp mRNA in Schwann cells. We show that sncRNA715 is expressed and its levels correlate inversely with MBP in cultured Schwann cells and in the sciatic nerve in vivo. Furthermore we could reduce MBP protein levels in cultured Schwann cells by increasing the levels of the inhibitory sncRNA715. Our findings suggest similarities in sncRNA715-mediated translational repression of Mbp mRNA in oligodendrocytes and Schwann cells.     

Functional divergence of a heterochromatin‐binding protein during stickleback speciation

Intragenomic conflict, the conflict of interest between different genomic regions within an individual, is proposed as a mechanism driving both the rapid evolution of heterochromatin‐related proteins and the establishment of intrinsic genomic incompatibility between species. Although molecular studies of laboratory model organisms have demonstrated the link between heterochromatin evolution and hybrid abnormalities, we know little about their link in natural systems. Previously, we showed that F₁ hybrids between the Japan Sea stickleback and the Pacific Ocean stickleback show hybrid male sterility and found a region responsible for hybrid male sterility on the X chromosome, but did not identify any candidate genes. In this study, we first screened for genes rapidly evolving under positive selection during the speciation of Japanese sticklebacks to find genes possibly involved in intragenomic conflict. We found that the region responsible for hybrid male sterility contains a rapidly evolving gene encoding a heterochromatin‐binding protein TRIM24B. We conducted biochemical experiments and showed that the binding affinity of TRIM24B to a heterochromatin mark found at centromeres and transposons, histone H4 lysine 20 trimethylation (H4K20me3), is reduced in the Japan Sea stickleback. In addition, mRNA expression levels of Trim24b were different between the Japan Sea and the Pacific Ocean testes. Further expression analysis of genes possibly in the TRIM24B‐regulated pathway showed that some gypsy retrotransposons are overexpressed in the F₁ hybrid testes. We, therefore, demonstrate that a heterochromatin‐binding protein can evolve rapidly under positive selection and functionally diverge during stickleback speciation.