Evolution of North American PVYNTN Strain Tu 660 from Local PVYN by Mutation rather than Recombination

A North American (NA) isolate of tobacco veinal necrotic strain of Potato virus Y (PVY^N) (N-Jg) and a NA isolate of potato tuber necrotic strain of Potato virus Y (PVY^NTN) (Tu 660) were tested for their phenotypes by inoculation to potato plants of three potato cultivars. Upon inoculation with Tu 660, tubers of the cultivars Norchip and Ranger Russet developed potato tuber necrotic ringspot disease (PTNRD) but not the tubers of Russet Burbank. N-Jg failed to induce PTNRD in the tested cultivars. The genomic RNAs of both strains were completely sequenced and analysed. High homology (98% and 99% identity on nucleotide and polyprotein, respectively) was found between Tu 660 and N-Jg. When polyproteins were compared with other isolates, high identity was observed between Tu 660 and an European (Eu) PVY^N-605 (98%) and with an Eu-PVY^NTN-H (96%). However, when individual mature proteins were compared, much lower identities (86.5–94%) were found between Tu 660 and PVY^NTN-H compared to 98–99.5% between Tu 660 and PVY^N-605 in the P3, 6K1 and CI regions. Further sequence analysis indicated that the PVY^NTN-H is a hybrid molecule of the genomic RNA recombination of PVY^O and Eu-PVY^N as shown by Glais et al. (Arch Virol 147, 363–378), whereas NA-PVY^NTN Tu 660 is free of recombination points. Phylogenetic analysis confirmed this observation, and suggested that, in light of high homology, the Tu 660 might have evolved from NA-PVY^N by mutations rather than the genome recombinations. The non-recombinant nature of NA-PVY^NTN Tu 660 strongly suggests that the recombinant structure of genome is not a necessary prerequisite for the PTNRD phenotype.     

Sequence Analysis of the RNA Polymerase Gene of Foot-and-Mouth Disease Virus Serotype Asia1

The complete nucleotide (nt.) sequence of the RNA polymerase (3D) gene and 81 nt. in the 3-untranslated region of foot-and-mouth disease virus (FMDV) serotype Asia1 (IND63/72) was determined and compared with the sequence of other FMDV serotypes. The 3D genomic region was 1410 nt. long encoding 470 amino acids with an inframe stop codon (TAA) at nt. position 1411–1413. The deduced amino acid sequence of the protein showed 8 conserved motifs as reported in other picornaviruses, 2 of which are 100% identical across the serotypes. Antigenic regions in the polymerase protein were predicted and found to be located at the N-terminus of the protein. The phylogenetic analysis showed that the FMD viruses were segregated into different clusters based on geographical origin; the Asia1 virus did not cluster tightly with any of the geographical groups.     

Comparison of ultrasonographic findings in spontaneous abortions with normal and abnormal karyotypes

To determine whether ultrasonographic findings can predict the karyotype of spontaneous abortions, 137 pregnancies (54 spontaneous, 83 assisted ovulatory cycles) that subsequently aborted and had chromosome analysis performed on the products of conception were studied ultrasonographically. Transvaginal ultrasound was performed using an Acuson 128XP/10 with 7.5 MHz probe. The numbers of empty gestational sacs, small and normal for gestational size, embryonic poles and embryos with documented cardiac activity were calculated. The frequency of each of these findings in pregnancies with normal and abnormal karyotypes was compared. Of the 137 spontaneous abortions, 51 had normal chromosome analyses and 86 had abnormal karyotypes (68 aneuploidies and 18 polyploidies). Ultrasonographic findings in the 51 karyotypically normal pregnancies included 16 (31%) with empty gestational sacs, and 35 (69%) with embryonic poles, of which 24 (69%) were at least 1 week smaller than expected for gestational age and 11 (31%) were the expected size. Embryonic cardiac activity was documented in 22 (63%) of the 35 embryonic poles. Amongst 86 pregnancies with abnormal karyotypes, similar frequencies of ultrasound findings were found: 23 (27%) with empty gestational sacs, 42 (67%) with embryonic poles smaller than expected for gestational age, and 50 (79%) embryos lost after documentation of embryonic cardiac activity. No differences in the frequency of ultrasonographic findings of empty gestational sacs, small embryonic pole and embryonic cardiac activity were observed between karyotypically normal and abnormal spontaneous abortions. Ultrasonographic findings cannot predict the karyotype of spontaneous abortions.      

Gonadotrophin-releasing hormone agonist dose-dependency of pituitary desensitization during controlled ovarian hyperstimulation in IVF

The aim of this study was to find the minimal effective daily s.c. dose of the gonadotrophin-releasing hormone (GnRH) agonist, triptorelin acetate, that suppresses the GnRH-induced release of luteinizing hormone (LH) at time of human chorionic gonadotrophin (HCG) injection and thereby prevents spontaneous LH surges during in-vitro fertilization (IVF) stimulation cycles. Therefore, a double-blind, prospective and randomized titration study was performed. A total of 48 IVF patients were divided into four groups of 12 patients. Each group received a different dose of triptorelin acetate, namely 5, 15, 50 or 100 microg s.c. daily. Standard ovarian stimulation was carried out using urinary follicle stimulating hormone (FSH) preparations. A 500 microg GnRH test was performed 90 min before the HCG injection in order to measure the degree of pituitary desensitization. Spontaneous LH surges were not detected in any of the groups, although three patients in the 5 microg group had ovulated at the time of ovum retrieval. The pituitary LH response to the GnRH test at time of HCG, expressed as area under the curve (AUC), appeared to be dose-dependent. Thus, a daily s.c. dose of 100 microg triptorelin acetate appears to be too high, since adequate desensitization of the pituitary (i.e. no spontaneous LH surge) can be achieved with doses as low as 15 and 50 microg.