bluuebunny/crossref_metadata_2025_split huggingface dataset:
Advantages of sexual reproduction
Authors: Crow James F. 
Published: May 2005

AbstractDespite the obvious efficiencies of many forms of asexual reproduction, sexual reproduction abounds. Asexual species, for the most part, are relatively short‐lived offshoots of sexual ancestors. From the nineteenth century, it has been recognized that, since there is no obvious advantage to the individuals involved, the advantages of sexual reproduction must be evolutionary. Furthermore, the advantage must be substantial; for example, producing males entails a two‐fold cost, compared to dispensing with them and reproducing by parthenogenetic females.There are a large number of plausible hypotheses. To me the most convincing of these are two. The first hypothesis, and the oldest, is that sexual reproduction offers the opportunity to produce recombinant types that can make the population better able to keep up with changes in the environment. Although the subject of a great deal of work, and despite its great plausibility, the hypothesis has been very difficult to test by critical observations or experiments.Second, species with recombination can bunch harmful mutations together and eliminate several in a single “genetic death.” Asexual species, can eliminate them only in the same genotype in which they occurred. If the rate of occurrence of deleterious mutations is one or more per zygote, some mechanism for eliminating them efficiently must exist. A test of this mutation load hypothesis for sexual reproduction, then, is to find whether deleterious mutation rates in general are this high‐as Drosophila data argue. Unfortunately, although molecular and evolutionary studies can give information on the total mutation rate, they cannot determine what fraction are deleterious.In addition, there are short discussions of the advantages of diploidy, anisogamy, and separate sexes. © 1994 Wiley‐Liss, Inc.
Regulatory rearrangements and smg‐sensitive allels of the C. elegans sex‐determining gene tra‐1
Authors: Zarkower David , De Bono Mario , Aronoff Rachel , Hodgkin Jonathan 
Published: May 2005

AbstractThe tra‐1 gene is the terminal regulator in the sex determination pathway in C. elegans, directing all aspects of somatic sexual differentiation. Recessive loss‐of‐function (If) mutations in tra‐1 masculinize XX animals (normally somatically female), while dominant gain‐of‐function mutations feminize XO animals (normally male). Most tra‐1(If) mutations can be fitted into a simple allelic series of somatic masculinization, but a small number of If alleles do not fit into this series. Here we show that three of these mutations are associated with DNA rearrangements 5′ to the coding region. One allele is an inversion that may be subject to a position effect. We also report the isolation of a new class of tra‐1 alleles that are responsive to mutations in the smg system of RNA surveillance. We show that two of these express RNAs of aberrant size. We suggest that the smg‐sensitive mutations may identify a carboxy‐terminal domain required for negative regulation of tra‐1 activity. © 1994 Wiley‐Liss, Inc.
Sex determination in Drosophila melanogaster: X‐linked genes involved in the initial step of Sex‐lethal activation
Authors: Śnchez Lucas , Granadino Begoña , Torres Miguel 
Published: May 2005

AbstractSex determination is the commitment of an embryo to either the female or the male developmental pathway. The ratio of X chromosomes to sets of autosomes is the primary genetic signal that determines sex in Drosophila, by triggering the functional state of the gene Sex‐lethal: in females (2X;2A) Sxl will be ON, whereas in males (X;2A) Sxl will be OFF. Genetic and molecuar studies have defined a set of genes involved in the formation of the X:A signal, as well as other genes, with either maternal or zygotic effects, which are also involved in regulating the initial step of Sex‐lethal activation. We review these data and present new data on two more regions of the X chromosome that define other genes needed for Sxl activation. In addition, we report on the interaction between some of the genes regulating Sxl activation. © 1994 Wiley‐Liss, Inc.
Sxl in the germline of Drosophila: A target for somatic late induction
Authors: Steinmann‐Zwicky Monica 
Published: May 2005

AbstractIn Drosophila, the sex of germ cells is determined by autonomous and inductive signals. Somatic inductive signals can drive XX germ cells into oogenesis or into spermatogenesis. An autonomous signal makes XY germ cells male and unresponsive to sex determination by induction. The elements forming the X:A ratio in the soma and the genes tra, tra2, dsx, and ix that determine the sex of somatic cells have no similar role in the germline. The gene Sxl, however, is required for female differentiation of somatic and germ cells. Inductive signals that are dependent on somatic tra and dsx expression already affect the sex‐specific development of germ cells of first instar larvae. At this early stage, however, germline expression of Sxl does not appear to affect the sexual characteristics of germ cells. Since inductive signals dependent on tra and dsx nevertheless influence the choice of sex‐specific splicing of Sxl, it can be concluded that Sxl is a target of the inductive signal, but that its product is required late for oogenesis. Other genes must therefore control the early sexual dimorphism of larval germ cells. © 1994 Wiley‐Liss, Inc.
Hemoglobin switching in Rana/Xenopus erythroid heterokaryons: Factors mediating the metamorphic hemoglobin switch are conserved
Authors: Broyles Robert H. , Ramseyer Lawrence T. H. , Do Thuy H. , McBride Kari A. , Barker Janet C. 
Published: May 2005

AbstractHemoglobin switching, which occurs in all classes of vertebrates as well as in certain invertebrates, is due to developmental regulation of different globin genes which are typically arranged in clustered families. By fusing erythroid cells of different developmental programs, trans‐acting factors that regulate this switch in gene expression have been detected [Ramseyer et al. (1989): Dev Biol 133:262‐271]. Adult erythroid cells of one anuran species, Xenopus laevis, were fused with tadpole erythroid cells of another frog, Rana catesbeiana, creating developmental erythroid heterokaryons that synthesize adult Rana globin mRNA and hemoglobins. The results show that factors from adult Xenopus erythroid cells are capable of inducing adult Rana globin gene expression in the Rana tadpole erythroid cell nucleus. We have used the cross‐induction of adult Rana hemoglobin synthesis in these adult Xenopus/Rana tadpole erythroid heterokaryons to address two practical questions, answers to which may be helpful in isolating developmental stage‐specific globin gene regulatory proteins: (1) Are erythroblasts which are actively expressing globin mRNAs and hemoglobins richer in specific globin‐inducing activities than other stages of erythroid cellular differentiation? (2) Do mature, circulating erythrocytes still have the activities necessary to mediate the cross‐induction of Hb synthesis? The results reported here show that the answers to both questions are affirmative and show that quiescent, fully differentiated adult erythroid cells are still capable of expressing the trans‐activator(s). These findings show that factors which mediate the metamorphic hemoglobin switch are conserved between these two genera of frogs. © 1994 Wiley‐Liss, Inc.
Characterization and expression of C/EBP‐like genes in the liver of Rana catesbeiana tadpoles during spontaneous and thyroid hormone‐induced metamorphosis
Authors: Chen Yuqing , Hu Huimin , Atkinson Burr G. 
Published: May 2005

AbstractTissue‐specific changes in gene expression occur in the liver of Rana cafesbeiana tadpoles undergoing metamorphosis. Many of these changes can be induced precociously by administration of thyroid hormone (TH) to a tadpole or to cultured tadpole liver. While the precise molecular means by which TH exerts a tissue‐specific response is unknown, recent studies suggest that the expression of genes which are liver‐specific and characteristic of the adult liver phenotype may rely on TH‐induction of tissue‐specific transcription factors, as well as the thyroid hormone receptor proteins. Guided by this notion, we screened our Rana catesbeiana liver cDNA library and isolated clones, RcC/EBP‐1 and ‐2, encoding Rana homologues of a mammalian transcription factor, C/EBP (CCAAT/enhancer core binding protein), implicated in the expression of liver‐specific genes and terminal differentiation of hepatocytes. Gel mobility shift assays demonstrate that the proteins synthesized from these cDNAs bind specifically to the consensus binding site for C/EBP‐related proteins. Characterization of the amino acid sequence in the bZlP DNA‐binding domains of these proteins suggests that RcC/EBP‐1 and ‐2 encode Rana homologues of C/EBPα and δ, respectively. Hybridization analyses demonstrate that the amount of RcC/EBP‐2 mRNAs in tadpole liver remains constant throughout metamorphosis, whereas RcC/EBP‐1 mRNAs are up‐regulated during both spontaneous and TH‐induced metamorphosis. The TH‐induced up‐regulation of RcC/ EBP‐1 mRNAs precedes the up‐regulation of liver‐specific urea cycle enzyme mRNAs by 6 to 12 hours. These results, coupled with in situ hybridization studies, suggest that RcC/EBP‐1 mRNAs encode a transcription factor which may play an early role(s) in the terminal differentiation and/or reprogramming of gene expression in this tadpole's liver cells during both spontaneous and TH‐induced metamorphosis. ©1994 WiIey‐Liss, Inc.
Cloning of thyroid hormone receptor genes expressed in metamorphosing flounder
Authors: Yamano Keisuke , Araki Kazuo , Sekikawa Kenji , Inui Yasuo 
Published: May 2005

AbstractTwo distinct cDNAs encoding thyroid hormone receptors (THRs) were cloned from a λ gtl0 library prepared from the whole bodies of metamorphosing flounder larvae (Paralichfhys olivaceus). Deduced amino acid sequences of the two isolated cDNAs shared 96% and 92% homologies in their DNA‐ and hormone‐binding domains, respectively. These were highly conserved when compared to THRs for other vertebrates: 88–96% in the DNA‐binding domain and 84–94% in the hormone‐binding domain. Other receptors in the nuclear receptor family showed lower homologies than those of THRs. Both THRs for the flounder had higher homologies with the α‐type THRs of other vertebrates than with the β‐type. Thus, the two THRs for flounder were designated as fTHRαA and fTHRαB. © 1994 Wiiey‐Liss, Inc.
Regulation of juvenile hormone esterase gene transcription by juvenile hormone
Authors: Venkataraman Venkateswar , O'Mahony Patrick J. , Manzcak Maria , Jones Grace 
Published: May 2005

AbstractJuvenile hormone (JH) is a major hormone regulating insect development. We have obtained a cDNA and a genomic clone for juvenile hormone esterase (JHE), the enzyme that is involved in the degradation of juvenile hormone and which is critical for insect development. Analysis of the regulation of JHE during the final larval stadium in the cabbage looper, Trichoplusia ni, showed that the JHE mRNA levels are maximal on days 2 and 4 of the final stadium. Nuclear run‐on analyses demonstrated that changes in JHE mRNA levels are primarily due to changes in the transcription rate of the gene, which may be a single copy in the genome. Treatment with a JH analog resulted in induction of JHE gene transcription, which could be detected within three hours after treatment. Salient features present in the 5′ flanking region of this JH‐sensitive gene are presented, including the presence of sequences closely resembling binding sites for members of the family of nuclear receptors. This report is the first direct demonstration, by nuclear run‐on analysis, of JH induction of gene transcription. © 1994 Wiley‐Liss, Inc.
Analysis of multiple classes of abscisic acid‐responsive genes during embryogenesis in zea mays
Authors: Williams Bruce A. , Tsang Adrian 
Published: May 2005

AbstractWe have examined the effects of the plant growth regulator abscisic acid (ABA), on the accumulation of three transcripts during maize embryogenesis. The Emb5 and Rab ‐17 transcripts were first detected during mid embryogenesis and accumulated to high levels during late embryogenesis. In an ABA‐deficient mutant, both transcripts were accumulated at very low levels. Treatment with μM ABA during early and mid embryogenesis, but not during late embryogenesis, in the wild type and the ABA‐deficient mutant enhanced the accumulation of the Emb5 and Rab‐17 transcripts. The oleosin KD18 transcript was detected at moderate levels during early embryogenesis, reached a peak during mid embryogenesis and then declined gradually. Embryos incubated in the absence of ABA exhibited a rapid loss of the oleosin KD18 transcript whereas a high level of accumulation of this transcript was maintained by incubation with nM ABA. Interestingly, the oleosin KD18 transcript was accumulated at high levels in the ABA‐deficient mutant and was also detected, albeit at low levels, in an ABA‐insensitive mutant. In addition, the Rab‐17 transcript could be stimulated to accumulate in vegetative tissue by either ABA or water stress. Similar treatment of vegetative tissue did not induce the accumulation of Emb5 or oleosin KD18 transcripts. These results suggest that ABA‐responsive genes expressed during maize embryo‐genesis are regulated by multiple mechanisms. © 1994 Wiley‐Liss, Inc.
DNA sequence requirements for the regulation of immobilization antigen a expression in Paramecium tetraurelia
Authors: Martin Linda D. , Pollack Sidney , Preer John R. , Polisky Barry 
Published: May 2005

AbstractThe Paramecium surface proteins (immobilization antigens) are expressed in a mutually exclusive manner; only one antigen is found on the cell surface at a time. Expression of these proteins is regulated in response to environmental cues such as temperature and pH. This regulation has been shown to be controlled at the level of mRNA abundance by transcriptional and post‐transcriptional mechanisms. Here, we have studied the transcription and regulated expression of the immobilization antign A gene in Paramecium tetraurelia by transforming an A ‐deficient strain, d12, with cloned portions of the A gene viamicroinjection. The A gene is approximately 8 kilobases (kb) long with the transcription start site at postion −9 or −8 and the start of translation at position +1. Paramecia transformed with cloned DNA containing A‐gene sequences beginning at position −264 and ending 63 base pairs (bp) past the gene's polyadenylation site show properly regulated expression of immobilization antigen A. Lines derived from paramecia transformed with a plasmid containing A‐gene sequences starting at position −211, however, show markedly reduced A‐gene mRNA levels, and rarely express the A antigen. Nevertheless, cells that do express the A protein exhibit mutual exclusion and normal responses to environmental stimuli. Thus, the 54 bp between −264 and −211, while important for transcription, are not involved in the control of mutual exclusion and responses to environmental chages. Further deletion to position −151 yields similar, but more extreme, results. Therefore, the start of the A‐gene promoter lies within the region −264 to −211, with additional sequences affecting transcriptional regulation present between base pairs −211 and −151. Sequences controlling environmental responses and mutual exclusion must be located downstream of position −211. Thus, we have defined regions of DNA necessary for immobilization antigen A expression and have located the approximate position of the A‐gene promoter in Paramecium. This work paves the way for a precise mutational analysis of these regions and the first detailed molecular characterization of a Paramecium promoter. © 1994 Wiley‐Liss, Inc.
Fusome asymmetry and oocyte determination in Drosophila
Authors: Lin Haifan , Spradling Allan C. 
Published: May 2005

AbstractGermline cysts containing 16 interconnected cells (cystocytes) are produced at an early stage of Drosophila oogenesis by progenitor cells known as cystoblasts that undergo four synchronous rounds of incomplete division. During cyst formation, a region of specialized, spectrin‐rich cytoplasm called the fusome traverses the intercellular Connections (ring canals), linking individual cystocytes. Subsequently, 15 cystocytes begin to transport specific RNAs and other components into the remaining cell, the future oocyte. We used fusome‐specific antibodies to characterize the early stages of cyst formation. During the first cystoblast division, a spherical mass of fusome material (the “spectrosome”) was associated with only one pole of the mitotic spindle, revealing that this division is asymmetric. During the subsequent three divisions, the growing fusome always associated with the pole of each mitotic spindle that remained in the mother cell, and only extended through the newly formed ring canals after each division was completed. These observations suggest that fusomes help establish a system of directional transport between cystocytes that underlies oocyte determination. © 1995 Wiley‐Liss, Inc.
Unusual cytoskeletal and chromatin configurations in mouse oocytes that are atypical in meiotic progression
Authors: Albertini David F. , Eppig John J. 
Published: May 2005

AbstractMeiotic maturation progresses atypically in oocytes of strain LT/Sv and l/LnJ mice. LT/Sv occytes show a high frequency of metaphase l‐arrest and parthenogenetic activation. l/LnJ oocytes display retarded kinetics of meiotic maturation and a high frequency of metaphase l‐arrest. Some l/LnJ oocytes fail to resume meiosis. Changes in the configuration of chromatin, microtubules, and centrosomes are associated with specific stages of meiotic progression. In this study, the configuration of these subcellular components was examined in LT/Sv, l/LnJ, and C57BL/6J (control) oocytes either freshly isolated from large antral follicles or after culture for 15 hr to allow progression of spontaneous meiotic maturation. Differences were found in the organization of chromatin, microtubules, and centrosomes in LT/Sv and l/LnJ oocytes compared to control oocytes. For example, rather than exhibiting multiple cytoplasmic and nuclear centrosomes as in the normal germinal vesicle‐stage oocytes, LT/Sv oocytes typically contain a single large centrosome. In contrast, l/LnJ oocytes displayed many small centrosomes. The microtubules of normal germinal vesicle‐stage oocytes were organized as arrays or asters, but microtubules were shorter in LT/Sv oocytes and absent from l/LnJ oocytes. After a 15‐hr culture, centrosomal material of normal metaphase II oocytes was organized at both spindle poles. In contrast, metaphase l‐arrested LT/Sv oocytes exhibited an elongated spindle with centrosomal material appearing more organized at one pole of the spindle. Both control and LT/Sv oocytes displayed cytoplasmic centrosomes. Metaphase l‐arrested l/LnJ oocytes rarely had cytoplasmic centrosomes but exhibited centrosomal foci at the spindle periphery. Thus, oocytes that are atypical in the progression of meiotic maturation displayed aberrant configurations of microtubules and centrosomes, which are thought to participate in the regulation of meiotic maturation.
Estradiol regulates N‐cadherin mRNA levels in the mouse ovary
Authors: MacCalman Colin D. , Farookhi Riaz , Blaschuk Orest W. 
Published: May 2005

AbstractN‐cadherin (N‐cad) is a calcium‐dependent cell adhesion molecule which is present in the granulosa cells of the mouse ovarian follicle. This cell adhesion molecule has been implicated as a key modulator of follicular development. The regulators of N‐cad mRNA levels in the ovary have not been identified. We have examined the ability of steroids to influence ovarian N‐cad mRNA levels in vivo. Immature mice were injected with either progesterone, testosterone, 17β‐estradiol, or 17α‐estradiol. Only 17β‐estradiol caused a rapid and significant increase in the ovarian N‐cad mRNA levels. We speculate that this steroid is a major regulator of N‐cad‐mediated granulosa cell interactions in vivo. © 1995 Wiley‐Liss, Inc.
Is the sphere organelle/coiled body a universal nuclear component?
Authors: Gall Joseph G. , Tsvetkov Alexander , Wu Zheng'An , Murphy Christine 
Published: May 2005

AbstractWe present evidence for the essential homology of four nuclear organelles that have previously been described under four different names: coiled bodies in mammalian somatic nuclei, prenucleolar bodies in nuclei assembled in vitro in Xenopus egg extract, sphere organelles in amphibian germinal vesicles (GVs), and Binnenkörper in insect GVs. Each of these organelles contains coilin or a coilin‐related protein plus a variety of small nuclear ribonucleoproteins. We suggest that the sphere organelle/coiled body is a “universal” nuclear component in the sense that it is involved in common nuclear processes and hence will be found in one form or another in most eukaryotic cells. We postulate that it functions in the assembly and sorting of snRNP complexes for three RNA processing pathways: pre‐mRNA splicing, rRNA processing, and histone pre‐mRNA 3′ end formation. Specifically, the sphere organelle/coiled body may be the initial site for assembly of processing complexes, which are then sorted to other places in the nucleus, where the actual RNA processing takes place. © 1995 Wiley‐Liss, Inc.
Polarization of mitochondria in the unfertilized mouse oocyte
Authors: Calarco Patricia G. 
Published: May 2005

AbstractMaturation of an immature oocyte into one capable of being fertilized involves tightly choreographed movements of chromosomes and organelles. The localizaton of mitochondria during maturation was studied in live mouse oocytes by confocal laser scanning microscopy (CLSM). Mitochondria were labeled with rhodamine 123 or Mitotracker (Molecular Probes, Eugene, OR) both of which are cell permeant and accumulate in mitochondria; acridine orange was used to mark chromatin. Prior to maturation, oocytes appeared to be radially symmetrical with no evident polarity; fully mature oocytes exhibited obvious polarity marked by the position of the metaphase II spindle in the cortex. CLSM revealed several interesting features of mitochondrial distribution: (1) A cortical clump of mitochondria was seen approximately 30‐45to one side of the metaphase II spindle and marked the region of polar body I extrusion. (2) Large foci of mitochondria (7–14μM) were frequently found around the central region of the mature oocyte, while the central region often exhibited markedly fewer mitochondria. (3) Small mitochondrial foci (3μM) in the cortex and near the GV characterized several oocytes which failed to mature. (4) Non‐spindle‐associated mitochondria were not uniformly distributed in the mature oocyte but were concentrated in the hemisphere containing the metaphase II spindle. (5) The distal margins of this mitochondrial hemisphere were sharply demarcated at the cortex. These findings should help us understand organelle localization during mammalian oocyte maturation, and may give insights into possible causes of infertility and into early events of preimplantation development. © 1995 Wiley‐Liss, Inc.