Characterization of the Skeletal Fusion with Sterility (sks) Mouse Showing Axial Skeleton Abnormalities Caused by Defects of Embryonic Skeletal Development

The development of the axial skeleton is a complex process, consisting of segmentation and differentiation of somites and ossification of the vertebrae. The autosomal recessive skeletal fusion with sterility (sks) mutation of the mouse causes skeletal malformations due to fusion of the vertebrae and ribs, but the underlying defects of vertebral formation during embryonic development have not yet been elucidated. For the present study, we examined the skeletal phenotypes of sks/sks mice during embryonic development and the chromosomal localization of the sks locus. Multiple defects of the axial skeleton, including fusion of vertebrae and fusion and bifurcation of ribs, were observed in adult and neonatal sks/sks mice. In addition, we also found polydactyly and delayed skull ossification in the sks/sks mice. Morphological defects, including disorganized vertebral arches and fusions and bifurcations of the axial skeletal elements, were observed during embryonic development at embryonic day 12.5 (E12.5) and E14.5. However, no morphological abnormality was observed at E11.5, indicating that defects of the axial skeleton are caused by malformation of the cartilaginous vertebra and ribs at an early developmental stage after formation and segmentation of the somites. By linkage analysis, the sks locus was mapped to an 8-Mb region of chromosome 4 between D4Mit331 and D4Mit199. Since no gene has already been identified as a cause of malformation of the vertebra and ribs in this region, the gene responsible for sks is suggested to be a novel gene essential for the cartilaginous vertebra and ribs.     

Desynapsis in Alocasia indica Schott

In a culture of Alocasia indica (2n=28), one plant was found to be desynaptic. At pachytene, pairing apparently was complete, but at diakinesis and metaphase I on the average only 2.36 and 1.53 bivalents respectively were found. Desynapsis is of the medium-strong type according to Prakken. Later meiotic stages were irregular and pollen sterility was 95%. The origin must have been spontaneous mutation.     

ZOOSPORIC FUNGI OF OCEANIA. VII. FUSIONS IN RHIZOPHLYCTIS

Clumping, pairing, and fusion of zoospores occur commonly in three isolates of Rhizophlyctis occanis sp. n., as well as in R. ingoldii Sparrow from the South Pacific islands and New Zealand. At present the fusions are interpreted to be gametic, but this interpretation has not been substantiated fully because it has not been possible so far to bring the fusion products to maturity and demonstrate conclusively that resting spores are sexually formed. The motile cells appear to be facultative. They may function as zoospores and develop directly into sporangial thalli or fuse to form young zygote-like thalli. In this respect they are very similar to those of some members of the Olpidiaceae and Synchytriaceae. The fusing cells lose their morphological identity as such in the process of fusion as in members of these families, and in this respect they are unlike most of those of the family Rhizidiaceae in which Rhizophlyctis is commonly classified. The fusions in R. occanis and R. ingoldii are strikingly similar to those in Karlingia dubia Karling, an operculate species, which indicates that Rhizophlyctis and Karlingia are closely related genera.     

Efficient DNA pairing in a Neurospora mutant defective in chromosome pairing

Summary A Neurospora crassa mutation, mei-2, affecting recombination and pairing of homologous chromosomes during meiosis, was characterized for its effect on repeat-induced point mutation (RIP). We found that RIP, which depends on recognition of DNA sequence homology, is not inhibited by mei-2, suggesting that the defect in chromosome pairing of this mutant is not due to a defect in DNA pairing and that DNA pairing is not dependent on chromosome pairing.     

Effects of several meiotic mutations on female meiosis in maize

A modified enzyme digestion technique of ovary isolation followed by staining and squash preparation has allowed us to observe female meiosis in normal maize meiotically dividing megaspore mother cells (MMCs). The first meiotic division in megasporogenesis of maize is not distinguishable from that in mi-crosporogenesis. The second female meiotic division is characterized as follows: (1) the two products of the first meiotic division do not simultaneously enter into the second meiotic division; as a rule, the chalazal-most cell enters division earlier than the micropylar one, (2) often the second of the two products does not proceed with meiosis, but degenerates, and (3) only a single haploid meiotic product of the tetrad remains alive, and this cell proceeds with three rounds of mitoses without any intervening cell wall formation to produce the eight-nucleate embryo sac. This technique has allowed us to study the effects of five meiotic mutations (aml, aml-pral, afdl, dsy *-9101, and dvl) on female meiosis in maize. The effects of the two alleles of the aml gene (aml and aml-pral) and of the afdl and dsy *-9101mutations are the same in both male and female meiosis. The aml allele prevents the entrance of MMCs into meiosis and meiosis is replaced by mitosis; the aml-pral permits MMCs to enter into meiosis, but their progress is stopped at early prophase I stages. The afdl gene is responsible for substitution of the first meiotic (reductional) division by an equational division including the segregation of sister chromatid centromeres at anaphase I. The dsy * -9101 gene exhibits abnormal chromosome pairing; paired homologous chromosomes are visible at pachytene, but only univalents are observed at diakinesis and metaphase I stages. These mutation specific patterns of abnormal meiosis are responsible for the bisexual sterility of these meiotic mutants. The abnormal divergent shape of the spindle apparatus and the resulting abnormal segregation of homologous chromosomes observed in micro-sporogenesis in plants homozygous for the dv1 mutation have not been found in meiosis of megasporogenesis. Only male sterility is induced by the dv1 gene in the homozygous condition. © 1993 Wiley-Liss, Inc.     

Replication factor C1 (RFC1) is required for double‐strand break repair during meiotic homologous recombination in Arabidopsis

Replication factor C1 (RFC1), which is conserved in eukaryotes, is involved in DNA replication and checkpoint control. However, a RFC1 product participating in DNA repair at meiosis has not been reported in Arabidopsis. Here, we report functional characterization of AtRFC1 through analysis of the rfc1–2 mutant. The rfc1–2 mutant displayed normal vegetative growth but showed silique sterility because the male gametophyte was arrested at the uninucleus microspore stage and the female at the functional megaspore stage. Expression of AtRFC1 was concentrated in the reproductive organ primordia, meiocytes and developing gametes. Chromosome spreads showed that pairing and synapsis were normal, and the chromosomes were broken when desynapsis began at late prophase I, and chromosome fragments remained in the subsequent stages. For this reason, homologous chromosomes and sister chromatids segregated unequally, leading to pollen sterility. Immunolocalization revealed that the AtRFC1 protein localized to the chromosomes during zygotene and pachytene in wild‐type but were absent in the spo11–1 mutant. The chromosome fragmentation of rfc1–2 was suppressed by spo11–1, indicating that AtRFC1 acted downstream of AtSPO11‐1. The similar chromosome behavior of rad51 rfc1–2 and rad51 suggests that AtRFC1 may act with AtRAD51 in the same pathway. In summary, AtRFC1 is required for DNA double‐strand break repair during meiotic homologous recombination of Arabidopsis.     

Cyto-morphological studies op some species and hybrids in the Eu-Sorghums

Summary Important morphological features such as plant height, leaf size and number of leaves, shape of the panicle and sessile spikelets, staminate condition of the pedicellate florets, nature of lemma, colour of the stigmatic surface and seeds etc., were studied in 8 Sorghum species and 10 F₁ hybrids between them. Based on the data, interrelationship amongst the species are discussed.Pachytene pairing was complete and apparently normal, followed by regular meiosis at later stages resulting in high pollen stainability and good seed setting in all the parental species except the male sterile Kafir. Studies on the pairing properties of the differentially stained regions showed that synapsis starts from the proximal to the distal end and separation of the split chromosomes starts from the distal to the proximal.The interspecific hybrids studied are classified into four types based on pachytene pairing and pollen sterility. 1. normal pairing accompanied by high pollen fertility, 2. normal pairing accompanied by partial pollen sterility. 3. irregularities in the pachytene pairing followed by partial pollen sterility and 4. irregularities in the pachytene pairing accompanied by normal pollen fertility. Suitable explanations are advanced to explain the meiotic aberrations noted in some of the hybrids under study.Cytogenetical mechanisms underlying species differentiation in the Eu-Sorghum species are discussed.     

Deletion of porcine BOLL is associated with defective acrosomes and subfertility in Yorkshire boars

A recessive sperm defect of Yorkshire boars was detected more than a decade ago. Affected boars produce ejaculates that contain spermatozoa with defective acrosomes, resulting in low fertility. The acrosome defect was mapped to porcine chromosome 15 but the causal mutation has not been identified. We re-analyzed microarray-derived genotypes of affected boars and confirmed that the acrosome defect maps to a 12.24 Mb segment of porcine chromosome 15. To detect the mutation causing defective acrosomes, we sequenced the genomes of two affected and three unaffected boars to an average coverage of 11-fold. Read depth analysis revealed a 55 kb deletion that is associated with the acrosome defect. The deletion encompasses the BOLL gene encoding the boule homolog, an RNA binding protein which is an evolutionarily conserved member of the DAZ (Deleted in AZoospermia) gene family. Lack of BOLL expression causes spermatogenic arrest and sperm maturation failure in many species. Boars that carry the deletion in the homozygous state produce sperm but their acrosomes are defective, suggesting that lack of porcine BOLL compromises acrosome formation. Our findings warrant further research to investigate the role of BOLL during spermatogenesis and sperm maturation in pigs.     

Knockout of the folate transporter <Emphasis Type="Italic">folt-1</Emphasis> causes germline and somatic defects in <Emphasis Type="Italic">C. elegans</Emphasis>

Background  

The C. elegans gene folt-1 is an ortholog of the human reduced folate carrier gene. The FOLT-1 protein has been shown to transport folate and to be involved in uptake of exogenous folate by worms. A knockout mutation of the gene, folt-1(ok1460), was shown to cause sterility, and here we investigate the source of the sterility and the effect of the folt-1 knockout on somatic function.     

The Arabidopsis U–box/ARM repeat E3 ligase AtPUB4 influences growth and degeneration of tapetal cells,and its mutation leads to conditional male sterility

Pollen formation is a complex developmental process that has been extensively investigated to unravel underlying fundamental developmental mechanisms and for genetic manipulation of the male‐sterility trait for hybrid crop production. Here we describe identification of AtPUB4, a U–box/ARM repeat‐containing E3 ubiquitin ligase, as a novel player in male fertility in Arabidopsis. Loss of AtPUB4 function causes hypertrophic growth of the tapetum layer. The Atpub4 mutation also leads to incomplete degeneration of the tapetal cells and strikingly abnormal exine structures of pollen grains. As a result, although the Atpub4 mutant produces viable pollen, the pollen grains adhere to each other and to the remnants of incompletely degenerated tapetal cells, and do not properly disperse from dehisced anthers for successful pollination. We found that the male‐sterility phenotype caused by the Atpub4 mutation is temperature‐dependent: the mutant plants are sterile when grown at 22°C but are partially fertile at 16°C. Our study also indicates that the AtPUB4‐mediated pathway acts in parallel with the brassinosteroid pathway in controlling developmental fates of the tapetal cells to ensure male fertility.     

A fragile gene

Fragile X syndrome is the most common cause of inherited mental retardation in humans. The fragile X gene (FMR1) has been cloned and the mutation causing the disease is known. The molecular basis of the disease is an expansion of a trinucleotide repeat sequence (CGG) present in the first exon within the 5′ untranslated region of the FMR1 gene. Affected individuals have repeat CGG sequences of above 200. As a result the gene is not producing protein. It has been shown that the FMR1 protein has RNA binding activity, but the function of this RNA binding activity is not known. The timing and mechanism of repeat amplification are not yet understood. An animal model for fragile X syndrome has been generated, which can be used to study the clinical and biochemical abnormalities caused by absence of FMR1 protein product.     

ps-2, the gene responsible for functional sterility in tomato, due to non-dehiscent anthers, is the result of a mutation in a novel polygalacturonase gene

The recessive mutation ps-2, which appeared spontaneously in tomato, confers functional male sterility due to non-dehiscent anthers. In this study, we isolated and characterized the PS-2 gene. A single nucleotide mutation in a novel tomato polygalacturonase gene is responsible for the ps-2 phenotype. The mutation in ps-2 is responsible for an alternative splicing during maturation of the pre-mRNA, which leads to an aberrant mRNA. Differentiation between ps-2 and wild type (PS-2) anthers only appears in the final developmental stage in which the stomium remains closed in the mutant. To our knowledge, this is the first functional sterility gene isolated in the Solanaceae family. The specific expression of the Arabidopsis homolog of PS-2 in the anther dehiscence zone suggests a conserved mode of action over the plant kingdom, which means that the repression of PS-2 homologs may be a potential way to introduce functional sterility in other species. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Kinase gene fusions in defined subsets of melanoma

Genomic rearrangements resulting in activating kinase fusions have been increasingly described in a number of cancers including malignant melanoma, but their frequency in specific melanoma subtypes has not been reported. We used break‐apart fluorescence in situ hybridization (FISH) to identify genomic rearrangements in tissues from 59 patients with various types of malignant melanoma including acral lentiginous, mucosal, superficial spreading, and nodular. We identified four genomic rearrangements involving the genes BRAF, RET, and ROS1. Of these, three were confirmed by Immunohistochemistry (IHC) or sequencing and one was found to be an ARMC10‐BRAF fusion that has not been previously reported in melanoma. These fusions occurred in different subtypes of melanoma but all in tumors lacking known driver mutations. Our data suggest gene fusions are more common than previously thought and should be further explored particularly in melanomas lacking known driver mutations.     

An unusual chromosome system in a leafhopper (Homoptera auchenorrhyncha)

An unidentified species of the genus Austroagalloides is shown to have 7_II+1_IV instead of the normal 11_II+XO configuration at metaphase I of meiosis in males. The quadrivalent manifests two types of pairing which ensures regular disjunction; normal chiasma-type pairing and distance pairing. It is suggested that the 7_II+1_IV form is derived from the 11_II+XO form by a series of fusions.     

A synthetic combination of mutations, including fs(1)pyr? Su(b) , r? Su(b) and b , causes female sterility and reduces embryonic viability in Drosophila melanogaster

A Drosophila melanogaster mutant, fs(1)pyr ^Su(b) , carrying a mutation that maps to the tip of the X chromosome, has been isolated. The mutation, when present alone, does not confer a detectable phenotype. However, this mutation causes female sterility and reduces embryonic viability when combined with mutations which deregulate the pyrimidine and β-alanine pools. Embryos that are homozygous for the mutations fs(1)pyr ^Su(b) , r ^Su(b) [previously designated as Su(b)] and b, and originate from a female parent homozygous for the three mutations show severely reduced viability. Newly laid eggs begin development normally, but the majority of the embryos die just before the eggs are due to hatch. Received: 15 May 1998 / Accepted: 18 January 1999     

Pachytene analysis in oryza

Summary Pachytene analysis was undertaken in 4 japonica-indica rice hybrids. In all these hybrids, pairing was exceedingly abnormal lending evidence for structural hybridity. Earlier investigators who analysed metaphase-I and later stages of meiosis concluded that sterility is due to genic causes. The present investigation clearly points out the chromosomal causes of sterility and makes possible a reinterpretation of (1) non-recovery of recombinant phenotypes and (2) the occurrence of albina and other mutations in hybrid progenies.     

Mutation of cyp19a1b results in sterile males due to efferent duct obstruction in Nile tilapia

The involvement of estrogen in male fertility has been well established in mammals. However, less is known about the role of estrogen in fish male reproduction. Our recent study revealed that Cyp19a1a deficiency had no effect on fertility in male fish. In this study, expression of Cyp19a1b, but not Cyp19a1a, was detected by immunohistochemistry in Leydig cells of tilapia testes. cyp19a1b mutation resulted in a significant decrease in the concentration of 17β‐estradiol in serum and sterility in XY fish, as no offspring were obtained when crossed with control XX fish at 240 days after hatching (dah). No sperm was obtained from the mature mutants by in vitro extrusion. Further examination of the mutant gonads revealed excessive semen accumulation and testicular hypertrophy. Semen collected from the mutant testes during autopsy contained sperm with a normal morphology that showed no significant differences in motility, VCL, BCF, STR, or fertility compared with control sperm. Efferent ducts from the mutant testes, which had low‐convolution levels, fewer branches, and no blood vessels observed inside the walls, were significantly smaller in size. qRT‐PCR analyses showed downregulated expression of ion exchange genes. There was increased apoptosis in the epithelial cells of the efferent ducts and other somatic cells of the testes as revealed by TUNEL staining, as well as upregulation of apoptosis gene expression in the mutants. At 360 dah, mutant fish showed testicular atrophy and efferent duct fibrosis. These results demonstrated that estrogen deficiency caused by Cyp19a1b mutation resulted in male sterility due to efferent duct obstruction.     

The dsy10 Mutation of Arabidopsis results in desynapsis and a general breakdown in meiosis

The proper pairing and recombination of chromosomes during prophase is essential for the formation of gametes during meiosis. As part of studies to identify genes required for homologous chromosome pairing and recombination during meiosis in plants, we characterized a number of T-DNA-tagged, male-sterile mutants of Arabidopsis. Preliminary cytological studies on one line, 7219 which is male and female sterile, suggested that the mutation may disrupt meiosis and result in the formation of aberrant microsporocytes and microspores. In this report we present the results of a detailed analysis of meiosis in microsporocytes of sterile plants to elucidate the nature of the 7219 mutation. Analysis indicates that the mutation usually results in a desynaptic phenotype, with ten sister chromatids observed prior to metaphase I in most cells. Based on this, we named the mutation dsy10. The presence of several other meiotic defects suggests that dsy10 may not be a typical desynaptic mutant. Received: 15 December 2000 / Accepted: 19 April 2001     

A new mouse mutation causing male sterility and histoincompatibility

Male sterility and histoincompatibility, mshi, is an autosomal recessive mutation in BALB/cBy mice that causes reduced testis size and sterility in homozygous males. The testes of homozygous mutants are highly disorganized and appear to have a block in the regulation of male germ cell proliferation. No heterozygous effect is detectable. Reproduction is unaffected in females carrying the mutation. The mutation also affects histocompatibility; most homozygous males and females reject sex-matched skin grafts from BALB/cBy mice. We used an intercross between BALB/cBy and CAST/Ei to map the mshi mutation to the proximal end of Chromosome (Chr) 10. The most likely gene order places the mutation between D10Mit80 and D10Mit16, near the interferon gamma receptor locus, Ifgr, which may be a candidate gene for this mutation. Received: 26 April 1996 / Accepted: 20 June 1996