The classical term germ cell determinant was defined to cover whole function of germ plasm, or morphologically remarkable cytoplasm localized in oocytes and germ cells. Since early 1970 consequential advances in technology, including microsurgery, genetic anatomy and gene manipulation, have allowed cytological and molecular analyses of pole plasm (germ plasm) in Drosophila embryos. A series of recent work has revealed that multiple factors or molecule species in pole plasm participate in a consecutive reactions resulting in germline formation. Two molecule species have been specified as playing roles in germline cell formation. One that participates in sequestering pole plasm from somatic environment is mitochondrial large ribosomal (mtlr) RNA, and the other involved in driving pole cells into the germline pathway is Nanos protein. Studies disclosed the roles of those two molecules are reviewed.
Repetitive DNA sequences (Hi-b; 209 bp in length) were isolated from the HindIII digests of the genomic DNA of the triploid ginbuna, Carassius auratus langsdorfi. Sequence analyses revealed that the Hi-b repetitive units were comprised of the complete coding regions of 5S rDNA (120 bp in size) and their 5' flanking regions. The sequences of the Hi-b units from the same individual were highly homogeneous. Southern blot hybridization to the Hi-b probe displayed intricate patterns that represented the presence of other repetitive units containing the Hi-b related sequences. A major family of repetitive sequences related to the Hi-b was then obtained by the polymerase chain reaction using asymmetry primers for the 5S coding regions. These 331-bp sequences (AZ5S's) contained 5S pseudogenes as well as the almost entire Hi-b sequences, and seemed to be the true 5S rDNAs. The tandem arrangements of the AZ5S sequences explained most of the complex results of Southern blots. Another class of intriguing repeat units (Hi-b-β and Hi-b-γ) were also isolated. Fluorescence in situ hybridization data revealed two major signals on a pair of homologous chromosomes and several minor signals on other chromosomes in the triploid ginbuna, indicating the existence of the 5S related sequences as several separate clusters. The major spots were shared with the tetraploid ginbuna and goldfish, but not with the diploid ginbuna. When the genomic organization of the Hi-b related sequences in other cyprinid fishes was examined, the hybridization patterns of the ginbuna were very simillar to those of the goldfish, but were clearly different from those of the gengorobuna. The carp genome showed less complex patterns. Thus, the present 5S rDNA-related sequences could be candidates for phylogenetic molecular markers for the crucian carp.
Maternal transmission of mitochondrial DNA (mtDNA) allows us to generate mtDNA congenic strain by repeating backcrosses of female mice to male mice of an inbred strain, which carries different mtDNA haplotype from that of the female progenitor. Since genetic backgrounds of inbred strains commonly used (e.g., C57BL/6J [B6] and BALB/c) are mainly derived from an European subspecies of Mus musculus domesticus, congenic strains, in which mtDNA originated from an Asian subspecies M. musculus musculus or an European species M. spretus, give in vivo condition that mismatch occurs between the mitochondrial and the nuclear genome. So far, little has been known how the mismatch condition affects the physiological phenotype of the mice. To address this question, we established two mtDNA congenic strains, C57BL/6J(B6)-mtSPR and BALB/c-mtSHH, which carry M. spretus- and M. m. musculus-derived mtDNAs, representing the conditions of interspecific and intersubspecific mitochondrial-nuclear genome mismatch, respectively. Using these congenic strains, we examined their physical performance by measuring their running time on a treadmill belt until exhaustion. The result clearly showed that the mtDNA congenic strains manifested a significant decrease in the level of physical performance, when compared with their progenitor strains. It also appeared that the congenic mice manifested growth rate. Thus, all results indicated that mismatch between the mitochondrial and the nuclear genome causes phenotypic changes in individuals of mice.
Genetic variation in an endangered tree species, Chionanthus retusus, was examined using enzyme electrophoresis. This species occurs in East Asia from Japan to Taiwan and southern China. In Japan, however, it occurs only in two restricted areas: at the northernmost tip of Tsushima Island between Japan and Korea, and in the eastern Gifu Prefecture (Tôno region) of central Honshu. In the Tôno region, the habitat of C. retusus is becoming fragmented under the influence of human activity and each stand contains a few individuals of C. retusus, while the population on Tsushima consists of approximately 1000 individuals. From the fossil evidence, C. retusus has been distributed continuously including the both two regions, and the present distribution is apparently relic in Japan. In contrast to the Tôno population, the population of Tsushima seems to be stable. Comparing the genetic diversity and differentiation of the populations between these two regions should shed light on how a relic woody long-lived plant keeps and/or looses its genetic diversity, and how a population differentiates from other disjunct populations. Allozyme electrophoresis of 18 loci for the Tôno region indicated that 22.2% of the loci are polymorphic (P) with a gene diversity of (h) 0.087. The population of Tsushima has 38.9% polymorphic loci and a gene diversity of 0.149. We could not find any spatial genetic structure of C. retusus in the Tôno region by spatial autocorrelation analysis. These results suggest that considerable genetic variation is still present in the Tôno region and the influence of the recent habitat fragmentation seems not so large, yet. Because C. retusus is a long-lived tree, the population history may hinder the effect of the fragmentation at present. The genetic diversity (GST) between the populations of the Tôno and Tsushima is 0.280, showing the genetic differentiation between these two regions has occurred.
Restriction fragment length polymorphisms (RFLPs) of the mitochondrial DNA (mtDNA) of 15 strains of lotus (Nelumbo nucifera and N. pentapetala) were analyzed using 13 rice mtDNA fragments that contained 16 known mitochondrial genes and open reading frames (ORFs) as probes for a DNA gel blot analysis. Five groups appeared as a result of the phylogenetic analysis based on the RFLP data. Ohgahasu (Ohga lotus) and Chuugokukodaibasu (Chinese ancient lotus), strains that were reared from seeds excavated from different ancient deposits were classified into the same group. In the course of this analysis, a unique quantitative variation of mtDNA that indicates a change in the composition of the population of mtDNAs during the evolution of this plant species was detected. In combination with the phylogenetic analysis, the difference in mtDNA composition was found to have generated after the divergence of five strains of N. nucifera from the other seven strains of N. nucifera analyzed in this study.
In order to elucidate the structural chromosome organization of the heterochromatic regions in sheep, we have used C-banding, silver-staining, sequential CDD technique and restriction endonuclease banding. By these banding techniques we obtained four fractions of repetitive DNA, the autosomal fractions A and B, the C fraction in the X chromosome, and the D fraction in the Y chromosome. Silver staining revealed active nucleolus organizer regions (NOR's) on the telomeric GC-rich areas of chromosomes 1, 2, 3, 4, and 25 which were digested with HaeIII restriction endonuclease.
A fine genetic map of the long arm of 5A in common wheat was generated by mapping 48 RFLP markers, in which 23 cDNAs were involved. That map was compared with the cytological map and a genetic map of the diploid obtained from a cross between Triticum monococcum and T. boeoticum. The marker distribution of the genetic map of common wheat almost correlated with the cytological distances, but some regions in which recombination was suppressed were found; these were around the centromere and in the region adjacent to the central C-banding region (L1.5). Promotion of recombination at the distal part of chromosome was not found. The marker order of the genetic map of common wheat was identical to that of the diploid, indicating that reciprocal translocation 4AL-5AL in wheat had taken place at the diploid level. Furthermore, this region was compared with the corresponding one of barley (5HL) and of rice (chromosome 9). Translocation was not detected in the barley chromosome, but paracentric inversion was found in comparison with the corresponding region of wheat. The translocation point in wheat seemed to correspond to the inversion point of barley, suggesting a hot-spot region for chromosome breakage. Strong suppression of recombination was found in the central part of 5HL. About two-thirds of the proximal region of wheat 5AL revealed synteny with the corresponding region of rice, whereas there was no such relation in the more distal portion. Longer genetic distances in the central part of 5AL, in comparison with the corresponding region of rice, were found, indicating the presence of factors that affect recombination frequencies. The analyses suggest that the proximal part of chromosome arm 5AL has been relatively conserved, whereas the distal part has undergone more extensive rearrangements during evolution.
The starfish Asterias amurensis that is a common species in Japanese waters shows the remarkable morphological variation in several characters such as colour pattern of body between local populations. The genetic differentiation and relationships among seven local Japanese populations were investigated by allozyme analysis. From the allozyme variation observed in 25 genetic loci coding for 14 enzymes, Nei's genetic distances between seven local populations were calculated and a biochemical dendrogram for seven populations was constructed. The dendrogram indicated that the Akkeshi (Hokkaido), Ushimado (Inland Sea), and Ise (Ise Bay) populations are much genetically differentiated from the other four populations, and that the degree of genetic differentiation between them was much higher than that between conspecific local populations. Judging from allozyme and morphological data, we conclude that the starfish A. amurensis from Japanese waters consists of at least three groups that are largely genetically divergent at subspecies or sibling species level.
Herein we develop the sire and dam model counterpart of the combined-merit animal model (CM-AM) method for marker-assisted best linear unbiased prediction (BLUP) of breeding values, and thus for marker-assisted selection. With the current procedure, a specific data-structure, such as that of carcass traits in meat animals, is assumed in order that the solutions may be equivalent to those in the CM-AM method. The resulting system of mixed model equations becomes compact with the total additive genetic merit considered, and with non-parent animal equations absorbed, relative to the CM-AM method. Hence, the current procedure is expected to be useful for marker-assisted BLUP of breeding values for particular quantitative traits, especially in large outbreeding populations with complex pedigrees where the fraction of non-parents is high. A numerical illustration is given using data on carcass weight in beef cattle.
Rhy-1, one mutant strain of Neurospora crassa which shows arrhythmicity at high temperature, has been isolated by DNA insertional mutagenesis. The phase, i.e., the time of the first maximum conidiaiton after transfer to continuous darkness, was delayed by several hours in comparison with that of the wild-type strain. Also, the germination of ascospores was seriously inhibited. The arrhythmicity which was observed at high temperatures may be due to a stoppage of the circadian clock.