Codon usage in the vertebrate hemoglobins and its implications

A study of codon usage in vertebrate hemoglobins revealed an evolutionary trend toward elevated numbers of CpG codon boundary pairs in mammalian hemoglobin alpha genes. Selection for CpG codon boundaries countering the generally observed CpG suppression is strongly suggested by these data. These observations parallel recently published experimental results that indicate that constitutive expression of the human alpha-globin gene appears to be determined by regulatory information encoded within the structural gene. The possibility is raised that, in the absence of selection, CpG decay can be used to date the evolutionary origin of a mammalian alpha pseudogene from its active alpha gene.      

Evolution of crystallins: expression of lens-specific proteins in the blind mammals mole (Talpa europaea) and mole rat (Spalax ehrenbergi)

The mole (Talpa europaea; Insectivora) and the mole rat (Spalax ehrenbergi; Rodentia) both have degenerated eyes as a convergent adaptation to subterranean life. The rudimentary eye lenses of these blind mammals no longer function in a visual process. The crystallin genes, which display a lens-specific expression pattern, were studied in these blind mammals and in related species with normal eyes by hybridizing their genomic DNAs with probes obtained from cDNA clones for alpha A-, alpha B-, and beta Bp-crystallins from calf and gamma 3- crystallin from the rat. For all crystallin genes examined, the hybridization signals of mole and mole rat genomic DNA were comparable, respectively, with those of shrew and of rat and mouse, normal-vision representatives of the orders Insectivora and Rodentia. The expression of the crystallins at the protein level was tested by using antiserum specific for alpha-crystallin in immunofluorescence reactions on lens sections of mole and mole rat eyes and by using antisera against the beta- and gamma-crystallins on sections of the mole eye. All antisera gave positive fluorescence reactions exclusively with lens tissue of these blind mammals, indicating that the crystallins are still normally expressed despite the fact that these lenses have had no function in a visual process in these mammals for at least many million years. These findings apparently imply that some unknown selective advantage has conserved the crystallin genes and their expression after the loss of normal function of the lenses.      

Coccidia from the Tiger Salamander, Ambystoma tigrinum, in Northeastern Colorado and in Northern New Mexico

SYNOPSIS. Oocysts of Eimeria ambystomae Saxe, 1955, Eimeria microcapi sp. n., and Eimeria urodela sp. n. are described from the tiger salamander, Ambystoma tigrinum , collected in Colorado and New Mexico. The oocysts of E. ambystomae are ellipsoid, 29.8 × 17.3 (24–38 × 15–25) μm, and the sporocysts lanceolate, 22.6 × 5.4 (16–27 × 5–7) μm. Oocyst and sporocyst residua are present, but not a polar granule and a micropyle. The oocysts and sporocysts of E. microcapi are ellipsoid, measuring respectively 38.1 × 25.3 (35-41 × 23-26) μm and 18.1 × 7.4 (16-19 × 6–8) μm. Oocyst and sporocyst residua, a micropyle (mean 3 μm), and a distinct micropyle cap (2 μm high) are present, but not a polar granule. The oocysts of E. urodela are spheroid, 22.2 (14-26) μm, and the sporocysts lanceolate, 16.3 × 5.8 (12-19 × 4-7) μm. Oocyst and sporocyst residua are present, but a polar granule and a micropyle are absent.     

Feline Ventricular Ganglion Cells

IN mammals, with the exception of artiodactyls and cetaceans, it is generally accepted that intrinsic cardiac ganglion cells are confined distally by the atrioventricular groove¹. This is interpreted as indicating that vagal influence is limited to the atrial and specialized tissues and this concept is supported by much physiological evidence. It has been suggested that, in dogs, the vagi exert a direct negative inotropic effect on the ventricles², although Furnival et al.³ found that this effect was relatively insignificant. Morphologists have, however, reported ventricular ganglion cells in primates^4–6. We offer here morphological evidence for the existence of ventricular ganglion cells in the cat.     

Ultrastructural Study of Schizogony in Eimeria callospermophili*

SYNOPSIS The development of 1st generation schizonts of Eimeria callospermophili was studied with cell cultures and with experimentally infected host animals, Spermophilus armatus. Sporozoite-shaped schizonts each had 5-10 nuclei and all of the organelles of the sporozoite; each nucleus had a nucleolus and an associated Golgi apparatus. In stages immediately preceding merozoite formation, an intranuclear spindle apparatus with conical polar areas were observed near the outer margin of each nucleus. Two centrioles, each having 9 single peripheral tubules and one central tubule, were observed near each pole in some specimens. Merozoite formation began internally, with anlagen of 2 merozoites developing near each nucleus. The inner membrane of the merozoites first appeared as 2 dense thickenings adjacent to the polar cones and centrioles; subpellicular microtubules appeared simultaneously. Two anterior annuli and the conoid formed between the 2 thickenings. Vesicles, possibly of Golgi origin, were located next to the forming inner membrane. As the forming merozoites underwent elongation, a rhoptries anlage, a Golgi apparatus, refractile bodies, and mitochondria were incorporated into each. Sporozoite-shaped schizonts with merozoite anlagen transformed into spheroid or ovoid schizonts; at this time the conoid, rhoptries, micronemes, and the inner membrane of the pellicle gradually disappeared; several small refractile bodies were formed from the larger one. When development was about 1/3 complete, the immature merozoites began to grow outward from the surface of the schizont. In this phase of development, the single surface membrane of the schizont became the outer membrane of the merozoite's pellicle, and additional organelles, including the nucleus, were incorporated. Finally, the merozoites became pinched off, leaving a residual body. Development in cell cultures and host tissues was similar. This type of schizogony, previously undescribed in Eimeria, is compared with corresponding stages of development in other species of Eimeria and Sporozoa.     

Growth and maturation of a North American fairy shrimp, Streptocephalus seali (Crustacea; Anostraca): a laboratory study

SUMMARY.

• 1 We evaluated survival, growth and time to maturation of the fairy shrimp, Streptocephalus seali Ryder, in the laboratory at various combinations of temperature and water hardness.
• 2 Both independent factors affected survival and growth of S. seali. Multiple regression analysis and response surface modelling predict that after 4 days, over 80% survival is obtained at temperatures from 14 to 28°C and water hardnesses from 60 to 130 mg CaCO₃ 1-^?1.
• 3 Growth rates of larvae were often maximum at physicochemical conditions other than those which had promoted maximum rates of survival. For example, after 12 days mean total body length was almost 12 mm in larvae which had been maintained at 34°C (80 mg CaCO₃ 1-^?1): the maximum survival rate had been obtained at 19°C. Total length was directly correlated with temperature at the lowest hardness tested, but not at the other two hardnesses (100 and 120 mg CaCO₃ 1-^?1). At the latter water hardnesses, total length was significantly less at 34°C than at 32°C on all three sampling occasions (4, 8 and 12 days post-hatch).
• 4 Similarly, developmental stage of larvae correlated well with temperature but larvae reared at 34°C did not develop more quickly than those reared at 32°C. After 12 days, most larvae at the two highest temperature treatments had developed at least to Stage 14 and many were nearly mature; at 17°C most larvae were still at Stage 10.
• 5 During our study of maturation rate of females we noted that egg production was initiated after completion of fourteen or fifteen moults. Mean time to maturation at 27°C (17.3±2.8 days) exceeded that at 32°C (12.3±2.6days). The minimum time to maturation of a shrimp was 9 days at 32°C.

     

The influence of high levels of brief or prolonged supplementary far-red illumination during growth on the photosynthetic characteristics, composition and morphology of Pisum sativum chloroplasts

Abstract. Peas were grown in controlled environments (12h white fluorescent light. ∼47 μmol photons m^-2 s 1/12 dark, 25 °C), using (1) 15-min far-red illumination at the end of each photoperiod (brief FR) to simulate the increase in the far-red/red ratio near the end of the day, and (2) high levels of supplementary far-red light (red:far-red ratio=0.04) during the entire photoperiod (long-term FR) to simulate extreme shade conditions under a plant canopy. Brief FR illumination led to marked morphological effects attributable to phytochrome regulation, namely, an increase in internodal length, but a decrease in leaflet area, chloroplast size and chlorophyll content per chloroplast compared with the control. Significantly, brief FR illumination had little or no effect on the amounts of the major chloroplast components (ribulose 1.5-biphosphate carboxylase, adenosine triphosphate synthase, cytochrome b/f complex and Photosystem II) relative to chlorophyll or Photosystem I, and the leaf photosynthetic capacities per unit chlorophyll were similar. In contrast, supplementing high levels of far-red light during the entire photoperiod not only led to the phytochrome effects above, but there was also a marked increase in leaf photosynthetic capacity per unit chlorophyll. due to increased amounts of the major chloroplast components relative to chlorophyll or Photosystem I. We hypothesize that supplementary far-red light, absorbed by Photosystem I, induced an increase in the major chloroplast components by a photosynthetic feedback mechanism. In fully greened leaves, we propose that the two photosystems themselves, rather than phytochrome, may be the predominent sensors of light quantity in triggering modulations of the stoichiometries of chloroplast components, which in turn lead to varying photosynthetic capacities.