Brain and sense organ anatomy and histology in hemoglobinless Antarctic icefishes (Perciformes: Notothenioidei: Channichthyidae)

The Channichthyidae, one of five Antarctic notothenioid families, includes 16 species and 11 genera. Most live at depths of 200-800 m and are a major component of fish biomass in many shelf areas. Channichthyids are unique among adult fishes in possessing pale white blood containing a few vestigal erythrocytes and no hemoglobin. Here we describe the brains of seven species and special sense organs of eight species of channichthyids. We emphasize Chionodraco hamatus and C. myersi, compare these species to other channichthyids, and relate our findings to what is known about brains and sense organs of red-blooded notothenioids living sympatrically on the Antarctic shelf. Brains of channichthyids generally resemble those of their bathydraconid sister group. Among channichthyids the telencephalon is slightly regressed, resulting in a stalked appearance, but the tectum, corpus cerebellum, and mechanoreceptive areas are well developed. Interspecific variation is present but slight. The most interesting features of channichthyid brains are not in the nervous tissue but in support structures: the vasculature and the subependymal expansions show considerable elaboration. Channichthyids have large accessory nasal sacs and olfactory lamellae are more numerous than in other notothenioids. The eyes are relatively large and laterally oriented with similar duplex (cone and rod) retinae in all eight species. Twin cones are the qualitatively dominant photoreceptor in histological sections and, unlike bathydraconids, there are no species with rod-dominated retinae. Eyes possess the most extensive system of hyaloid arteries known in teleosts. Unlike the radial pattern seen in red-blooded notothenioids and most other teleosts, channichthyid hyaloid arteries arise from four or five main branches and form a closely spaced anastomosing series of parallel channels. Cephalic lateral line canals are membranous and some exhibit extensions (canaliculi), but canals are more ossified than those of deeper-living bathydraconids. We conclude that, with respect to the anatomy and histology of the neural structures, the brain and sensory systems show little that is remarkable compared to other fishes, and exhibit little diversification within the family. Thus, the unusual habitat and a potentially deleterious mutation resulting in a hemoglobinless phenotype are reflected primarily in expansion of the vasculature in the brain and eye partially compensating for the absence of respiratory pigments. Neural morphology gives the impression that channichthyids are a homogeneous and little diversified group.     

Deoxyribonuclease II: structure and chromosomal localization of the murine gene, and comparison with the genomic structure of the human and three C. elegans homologs

Deoxyribonuclease II (DNase II) has been implicated in diverse functions including degradation of foreign DNA, genomic instability, and in mediating the DNA digestion associated with apoptosis. The production of a mouse deleted for DNase II would clearly help to discriminate these functions. We have cloned and sequenced the mouse gene encoding DNase II. It was found to have a similar intron/exon structure to the human gene, although introns 3 and 5 are considerably shorter. The gene is located on mouse chromosome 8. The order of genes at this locus is mGCDH, mEKLF, mDNase II, mSAST, which is the same order that these genes are found on human chromosome 19. The GenBank database contains incorrect expressed sequence tags (ESTs) for the 3' end of the mouse mRNA. Furthermore, the gene structure of two of the three homologs in C. elegans is also incorrectly predicted in the database. We have established the correct intron/exon structure for these genes and show the conserved sequence and structure of the C. elegans, murine and human genes.     

The nature of the diversity of Antarctic fishes

The species diversity of the Antarctic fish fauna changed notably during the 40 million years from the Eocene to the present. A taxonomically restricted and endemic modern fauna succeeded a taxonomically diverse and cosmopolitan Eocene fauna. Although the Southern Ocean is 10% of the worlds ocean, its current fish fauna consists of only 322 species, small considering the global diversity of 25,000–28,000 species. The fauna is reasonably well-known from a taxonomic perspective. This intermediate designation between poorly known and well-known indicates that new species are regularly being described. A conservative estimate of the number of undescribed species is 30–60; many of these may be liparids. On the Antarctic continental shelf and upper slope the fauna includes 222 species from 19 families of benthic fishes. The most speciose taxa are notothenioids, liparids and zoarcids, accounting for 88% of species diversity. Endemism for Antarctic species is also, coincidentally, 88%, at least threefold higher than in faunas from other isolated marine localities. Eight notothenioid families, including five that are primarily Antarctic, encompass a total of 44 genera and 129 species, 101 Antarctic and 28 non-Antarctic. The 101 Antarctic species make up 45% of the benthic species diversity in the Antarctic region. However, at the highest latitudes, notothenioids contribute 77% of the species diversity, 92% of the abundance and 91% of the biomass. Although species diversity is low compared to other shelf habitats, the nature of the adaptive radiation in organismal diversity among notothenioids is noteworthy in the marine realm. In some notothenioid clades phyletic diversification was accompanied by considerable morphological and ecological diversification. The exemplar is the benthic family Nototheniidae that underwent a habitat or depth related diversification centred on the alteration of buoyancy. They occupy an array of pelagic and benthopelagic habitats at various depths on the shelf and upper slope. Diversification in buoyancy is the hallmark of the nototheniid radiation and, in the absence of swim bladders, was accomplished by a combination of reduced skeletal mineralisation and lipid deposition. Although neutral buoyancy is found in only five species of nototheniids some, like Pleuragramma antarcticum, are abundant and ecologically important. Much work remains to be done in order to frame and to use phylogenetically based statistical methods to test hypotheses relating to the key features of the notothenioid radiation. To reach this analytical phase more completely resolved cladograms that include phyletically basal and non-Antarctic species are essential.     

Resistance to a protein farnesyltransferase inhibitor in Plasmodium falciparum

The post-translational farnesylation of proteins serves to anchor a subset of intracellular proteins to membranes in eukaryotic organisms and also promotes protein-protein interactions. Inhibition of protein farnesyltransferase (PFT) is lethal to the pathogenic protozoa Plasmodium falciparum. Parasites were isolated that were resistant to BMS-388891, a tetrahydroquinoline (THQ) PFT inhibitor. Resistance was associated with a 12-fold decrease in drug susceptibility. Genotypic analysis revealed a single point mutation in the beta subunit in resistant parasites. The resultant tyrosine 837 to cysteine alteration in the beta subunit corresponded to the binding site for the THQ and peptide substrate. Biochemical analysis of Y837C-PFT demonstrated a 13-fold increase in BMS-388891 concentration necessary for inhibiting 50% of the enzyme activity. These data are consistent with PFT as the target of BMS-388891 in P. falciparum and suggest that PFT inhibitors should be combined with other antimalarial agents for effective therapy.     

Universal newborn screening for Hb H disease in California

Newborn screening is an accepted public health measure to ensure that appropriate health care is provided in a timely manner to infants with hereditary/metabolic disorders. Alpha-thalassemia is a common hemoglobin (Hb) disorder, and causes Hb H (beta4) disease, and usually fatal homozygous alpha(0)-thalassemia, also known as Hb Bart's (gamma4) hydrops fetalis syndrome. In 1996, the State of California began to investigate the feasibility of universal newborn screening for Hb H disease. Initial screening was done on blood samples obtained by heel pricks from newborns, and stored as dried blood spots on filter paper. Hb Bart's levels were measured as fast-moving Hb by automated high-performance liquid chromatography (HPLC) identical to that currently used in newborn screening for sickle cell disease. Subsequent confirmation of Hb H disease was done by DNA-based diagnostics for alpha-globin genotyping. A criterion of 25% or more Hb Bart's as determined by HPLC detects most, if not all cases of Hb H disease, and few cases of alpha-thalassemia trait. From January, 1998, through June, 2000, 89 newborns were found to have Hb H disease. The overall prevalence for Hb H disease among all newborns in California is approximately 1 per 15,000. Implementation of this program to existing newborn hemoglobinopathy screening in populations with significant proportions of southeast Asians is recommended. The correct diagnosis would allow affected infants to be properly cared for, and would also raise awareness for the prevention of homozygous alpha(0)-thalassemia or Hb Bart's hydrops fetalis syndrome.     

The maternal store of the xlgv7 mRNA in full-grown oocytes is not required for normal development in Xenopus

We have attempted to analyze the function of a maternal mRNA xlgv7 which is distributed as an animal-vegetal gradient in stage 6 oocytes using a combination of antisense oligodeoxynucleotide injection into oocytes followed by in vitro maturation and fertilization. Injection of 20 ng of the antisense oligodeoxynucleotide resulted in the destruction of the xlgv7 mRNA to undetectable levels. Upon maturation and fertilization the resulting embryos develop with no specific defects suggesting that the maternal store of xlgv7 in stage 6 oocytes is not required and that the embryo can develop solely with the maternal store of the xlgv7 protein. Also, these results demonstrate the feasibility of this approach in destroying a specific maternal RNA and assaying its effect on development.     

Identification of a Conserved Residue of Foamy Virus Gag Required for Intracellular Capsid Assembly

In contrast to all retroviruses but similar to the hepatitis B virus, foamy viruses (FV) require expression of the envelope protein for budding of intracellular capsids from the cell, suggesting a specific interaction between the Gag and Env proteins. Capsid assembly occurs in the cytoplasm of infected cells in a manner similar to that for the B- and D-type viruses; however, in contrast to these retroviruses, FV Gag lacks an N-terminal myristylation signal and capsids are not targeted to the plasma membrane (PM). We have found that mutation of an absolutely conserved arginine (Arg) residue at position 50 to alanine (R50A) of the simian foamy virus SFV cpz(hu) inhibits proper capsid assembly and abolishes viral budding even in the presence of the envelope (Env) glycoproteins. Particle assembly and extracellular release of virus can be restored to this mutant with the addition of an N-terminal Src myristylation signal (Myr-R50A), presumably by providing an alternate site for assembly to occur at the PM. In addition, the strict requirement of Env expression for capsid budding can be bypassed by addition of a PM-targeting signal to Gag. These results suggest that intracellular capsid assembly may be mediated by a signal akin to the cytoplasmic targeting and retention signal CTRS found in Mason-Pfizer monkey virus and that FV Gag has the inherent ability to assemble capsids at multiple sites like conventional retroviruses. The necessity of Env expression for particle egress is most probably due to the lack of a membrane-targeting signal within FV Gag to direct capsids to the PM for release and indicates that Gag-Env interactions are essential to drive particle budding.