Chromosome analysis and FISH mapping of ribosomal DNA (rDNA), telomeric (TTAGGG)n and (GATA)n repeats in the leech Haemopis sanguisuga (L.) (Annelida: Hirudinea)

In the present paper the chromosome complement (n = 13; 2n = 26) of the common leech Haemopis sanguisuga (L.) (Annelida: Hirudinea: Hirudinidae) was analyzed using banding techniques and fluorescent in situ hybridization (FISH) with three repetitive DNA probes [ribosomal DNA (rDNA), (TTAGGG) _n and (GATA) _n ]. FISH with the rDNA probe consistently mapped major ribosomal clusters (18S–28S rDNA) in the pericentromeric region of one large metacentric chromosome pair; this region, which consisted of heterochromatin rich in GC base pairs, was preferentially stained by silver nitrate (Ag-NOR). The (TTAGGG) _n telomeric probe was hybridized with the termini of nearly all chromosomes, whereas the (GATA) _n probe did not label any chromosome areas.     

Sex-related genes expression in juveniles of red abalone,Haliotis rufescens (Swanson, 1822)

The red abalone, Haliotis rufescens (Swanson 1822), is an important species for commercial aquaculture in Mexico, with annual production levels around 68 t. Not surprisingly, there is great interest in increasing production and its cultivation success. In order to have a better understanding of the genes involved in the sexual differentiation, this study analyzed the early differential expression of eight sex-related genes (VCP 2.2, VERL, VTGI, DMRT1, FP, LYS, SARIP, TEKT A1) by RT-qPCR in abalones from 5 to 45 mm of shell length. Sex identification was evaluated using VERL and LYS genes expression levels. These genes differentiated females and males from 16 mm of shell length and above. All eight sex-specific genes showed expression in all organisms. However, their level was higher in the sex group to which they correspond. In contrast, differential expression levels occurred in individuals with a shell length of 26–35 mm and 36–45 mm. These results suggest that sex gene expression is not entirely sex specific, and sexual differentiation in red abalone occurs between 16 and 25 mm of shell length. More studies are needed to determine the function of these genes in the sex that they are not associated with.     

Intrachromosomal location of the telomeric repeat (TTAGGG)n

Eukaryotic telomeres are specialized DNA-protein structures that are thought to ensure chromosomal stability and complete replication of the chromosome ends. All telomeres which have been studied consist of a tandem array of G-rich repeats which seem to be sufficient for telomere function. Originally, the human telomeric repeat (TTAGGG)_n was assumed to be exclusively located at the very end of all human chromosomes. More recent evidence, however, suggests an extension into proterminal regions. Very little is known about the interstitial distribution of telomeric repeats. Here we present evidence for the presence of (TTAGGG)_n repeats in internal loci on the long and short arms of different human chromosomes. In addition, we studied the genomic organization of these repeats in more detail and discuss possible functions of interstitial telomeric repeats in the human genome.     

The human protein translin specifically binds single-stranded microsatellite repeats, d(GT)n, and G-strand telomeric repeats, d(TTAGGG)n: a study of the binding parameters

We have previously identified in human fibroblasts a multisubunit protein (designated PGB) that specifically bound single-stranded G-rich microsatellite DNA sequences. PGB was later found to be identical, or closely related to translin, an octameric protein that bound single-stranded DNA consisting of sequences flanking chromosomal translocations. Here, we report that recombinant translin binds single-stranded microsatellite repeats, d(GT)n, and G-strand telomeric repeats, d(TTAGGG)n, with higher affinities (Kdis approximately = 2 nM and Kdis approximately = 12.5 nM, respectively, in 100 mM NaCl and 25 degrees C) than the affinity with which it binds a prototypical sequence flanking translocation sites (Kdis approximately = 23 nM). Translin also binds d(GT)n and d(TTAGGG)n overhangs linked to double-stranded DNA with equilibrium constants in the nanomolar range. Formation of DNA quadruplexes by the d(TTAGGG)n repeats inhibits their binding to translin. A further study of the binding parameters revealed that the minimal length of d(GT)n and d(TTAGGG)n oligonucleotides that a translin octamer can bind is 11 nucleotides, but that such oligonucleotides containing up to 30 nucleotides can bind only a single translin octamer. However, the oligonucleotides d(GT)27 and d(TTAGGG)9 bind two octamers with negative cooperativity. Translin does not detectably bind single-stranded d(GT)n sequences embedded within double-stranded DNA. Based on our data, we propose that translin might be involved in the control of recombination at d(GT)n.d(AC)n microsatellites and in telomere maintenance.     

Effect of eight benthic diatoms as feed on the growth of red abalone (Haliotis rufescens) postlarvae

The growth rate of abalone post larvae of Haliotis rufescens fed ad libitum with a benthic monoalgal diatom culture maintained as monocultures on a semi-commercial scale, was evaluated and correlated with the biochemical composition of the diatoms. The cell size (7.0 × 4.0 μm to 21.0 × 7.5 μm), protein percentage (7.42% to 13.66%), and ash content (49.03% to 59.61%) were different among diatom strains; lipid percentage, nitrogen free extract, and energy content (Kcal g⁻¹) were similar among diatom strains. The values of essential and non-essential amino and fatty acids composition differed among diatom strains. Differences in the abalone shell length and orthogonal analyses revealed postlarval growth was dependent on the quality of the food source. Postlarvae abalone displaying the longest shell lengths were fed Nitzschia thermalis var. minor and Amphiprora paludosa var. hyalina (1,712.0 ± 61 μm and 1,709 ± 67 μm, respectively), followed by Navicula incerta (1,413.3 ± 43 μm). The fatty acid content of benthic diatoms and abalone growth rate were not correlated.     

Chromosomal Location of Ribosomal DNA (rDNA), (GATA)n and (TTAGGG)n Telomeric Repeats in the Neogastropod Fasciolaria Lignaria (Mollusca: Prosobranchia)

This paper reports on a successful application of fluorescent in situhybridization (FISH) with three repetitive DNA probes (ribosomal DNA (rDNA), (GATA)_nand (TTAGGG)_n) in the chromosomes of Fasciolaria lignaria(Mollusca: Prosobranchia: Neogastropoda). rDNA FISH consistently identified four chromosome pairs per spread in the three examined specimens. The telomeric sequence (TTAGGG)_nhybridized with termini of all chromosomes. GATA FISH revealed abundant, dispersed minisatellite regions which were not associated to the XY sex-determining mechanism as indicated by the absence of a Y specific pattern of labelling. This revised version was published online in July 2006 with corrections to the Cover Date.     

Patterns of serotonin and SCP immunoreactivity during metamorphosis of the nervous system of the red abalone,Haliotis rufescens

Larvae of the red abalone, Haliotis rufescens, rely on external chemical cues to trigger metamorphosis; thus, the timing of metamorphosis is depedent upon the larva's chance encounter with the appropriate substrate. We examined the effect of the timing of metamorphosis on the development of the central nervous system (CNS), concentrating on the pattern of serotonin and small cardioactive peptide- (SCP) immunopositive neurons in the cerebral ganglia. By 4 days postfertilization the cerebral ganglion has five pairs of serotonin-immunoreactive (IR) neurons, one pair of which (the V cells) innervate the velum. This complement of cells remains stable for as long as the larval stage persists but metamorphosis causes the rapid loss of the V cells. In the case of SCP-IR neurons, one pair is present prior to metamorphic competency, but as larvae continue to age in the absence of inducing cues, additional pairs are gradually added. Metamorphosis causes an acceleration in SCP-IR neuron addition. This separation of developmental patterns is well adapted for the inherent uncertainty of the timing of metamorphosis in abalone larvae. © 1992 John Wiley & Sons, Inc.     

Patterns of serotonin and SCP immunoreactivity during metamorphosis of the nervous system of the red abalone, Haliotis rufescens.

Larvae of the red abalone, Haliotis rufescens, rely on external chemical cues to trigger metamorphosis; thus, the timing of metamorphosis is dependent upon the larva's chance encounter with the appropriate substrate. We examined the effect of the timing of metamorphosis on the development of the central nervous system (CNS), concentrating on the pattern of serotonin and small cardioactive peptide- (SCP) immunopositive neurons in the cerebral ganglia. By 4 days postfertilization the cerebral ganglion has five pairs of serotonin-immunoreactive (IR) neurons, one pair of which (the V cells) innervate the velum. This complement of cells remains stable for as long as the larval stage persists but metamorphosis causes the rapid loss of the V cells. In the case of SCP-IR neurons, one pair is present prior to metamorphic competency, but as larvae continue to age in the absence of inducing cues, additional pairs are gradually added. Metamorphosis causes an acceleration in SCP-IR neuron addition. This separation of developmental patterns is well adapted for the inherent uncertainty of the timing of metamorphosis in abalone larvae.     

Interstitial hybridization sites of the (TTAGGG)n telomeric sequence on the chromosomes of some North American hylid frogs.

Interstitial hybridization sites for the (TTAGGG)n telomeric repeat sequence were present in all seven species of hylid frogs examined and in a triploid hybrid between two of the species. Intra- and interspecific differences and similarities in hybridization sites agreed with what is known about the systematics of these species. Chromosome fusions, fissions, and inversions do not appear to have played a role in the evolution of the interstitial sites for the telomeric repeat in the species examined.     

Variation in biochemical composition during gonad maturation of the tropical abalone Haliotis varia Linnaeus 1758 (Vetigastropoda: Haliotidae)

Biochemical changes in the body components during gonad maturation of the tropical abalone Haliotis varia were investigated using wild collected specimens from the Gulf of Mannar, on the southeast coast of India. The gonadosomatic index (GSI) and the hepatosomatic index (HSI) showed negative correlations throughout the study period as well as during the progression of gonad maturation stages. The highest GSI for both the sexes were in the ripe stages followed by late maturing stages. The HSI ranged from 2.97 to 6.71 in females, and 3.55 to 5.09 in males. Among the biochemical components analysed, lipid and carbohydrate contents showed significant variations in the different tissues of H. varia during the progress of gonad maturation. The highest protein content was in the foot muscle and the lowest was in the digestive gland. Total lipids in the ovary were always higher compared with that of the testis and the values ranged from 12.60 to 26.49%, registering the highest value in the ripe ovary. Gonad carbohydrate content was lower when the lipid content was higher, suggesting the conversion of carbohydrate to lipids. The present study demonstrates the role of nutrient translocation between body parts as an essential part of the reproductive physiology of abalone.     

Distribution of non-telomeric sites of the (TTAGGG)n telomeric sequence in vertebrate chromosomes

The intrachromosomal distribution of non-telomeric sites of the (TTAGGG)_n telomeric repeat was determined for 100 vertebrate species. The most common non-telomeric location of this sequence was in the pericentric regions of chromosomes. A variety of species showed relatively large amounts of this sequence present within regions of constitutive heterochromatin. We discuss possible relationships between the non-telomeric distribution of the (TTAGGG)_n sequence and the process of karyotype evolution, during which these sites may provide potential new telomeres.