bluuebunny/crossref_metadata_2025 huggingface dataset:
Advantages of sexual reproduction
Authors: Crow James F.
Published: May 2005

Despite 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

The 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

Sex 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

In 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

Hemoglobin 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

Tissue‐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

Two 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

Juvenile 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

We 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

The 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

Germline 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

Meiotic 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

N‐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

We 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

Maturation 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.
Deficiency analysis of female gametogenesis in maize
Authors: Vollbrecht Erik , Hake Sarah
Published: May 2005

Plants produce female gametes through mitotic division in the multicellular, meioticolly reduced (haploid) megagametophyte phase. In flowering plants, the megagametophyte is the embryo sac; female gametogenesis or megagametogenesis comprises the ontogeny of the embryo sac. As a step toward understanding the role of embryo sac‐expressed genes in megagametogenesis, development of normal, haploid embryo sacs in maize was compared with development of embryo sacs deficient for various small, cytologically defined chromosomal regions. This analysis allowed us to screen 18% of the maize genome, including most of chromosome arms 1L and 3L, for phenotypes due specifically to deletion of essential, embryo sac‐expressed genes. Confocal laser scanning microscopy of whole developing embryo sacs confirmed that normal megagameto‐genesis in maize is of the highly stereotyped, bipolar Polygonum type common to most flowering plants examined to date. Deficiency embryo sac phenotypes were grouped into three classes, suggesting each deficient region contained one or more of at least three basic types of haploid‐expressed gene functions. In the first group, three chromosome regions contained genes required for progression beyond early, free‐nuclear stages of embryo sac development. Maintaining synchrony between events at the two poles of the embryo sac required genes located within two deficiencies. Finally, three chromosome regions harbored loci required for generation of normal cellular patterns typical of megagametogenesis. This analysis demonstrates that the embryo sac first requires postmeiotic gene expression at least as early as the first postmeiotic mitosis. Furthermore, our data show that a variety of distinct, genetically separable programs require embryo sac‐expressed gene products during megagametogenesis, and suggest the nature of some of those developmental mechanisms. © 1995 Wiley‐Liss, Inc.
Developmental and genetic mosaic analysis of Drosophila m‐dy mutants: Tissue foci for behavioral and morphogenetic defects
Authors: Newby Laurel M. , Jackson F. Rob
Published: May 2005

Mutants of the Drosophila miniature‐dusky (m‐dy) gene complex display morphogenetic phenotypes (miniature or dusky) caused by a change in the size and/or shape of the epidermal cells comprising the adult wing. In addition to a dusky phenotype, certain Andante‐type mutants also exhibit lengthened circadian periods for two different behavioral rhythms. If the latter phenotype results from a direct effect on the circadian pacemaker, the Andante function should be required within the brain. In order to define the tissues that require the morphogenetic and behavioral functions, we have carried out a genetic mosaic analysis. This study demonstrates that normal wing morphogenesis is entirely dependent on the genotype of wing cells. Furthermore, temperature‐shift experiments with a temperature‐sensitive dy mutant indicate that the morphogenetic function is required during adult development, and after the cessation of wing epidermal cell proliferation. At this time in development, a columnar epithelium in the developing wing becomes flattened into the mature wing blade, and we postulate that the cell‐size defect of m‐dy mutants results from an alteration of this mor‐phogenetic process. In contrast to the wing mor‐phogenesis phenotype, the characterization of locomotor activity in mosaic adults revealed a strong correlation between the head genotype and the Andante circadian‐period phenotype. This result indicates that neural tissues mediate the rhythm function. Thus, the behavioral and morphogenetic functions require gene expression in distinct tissues. Furthermore, the behavioral results are consistent with a requirement for Andante function within circadian pacemaker neurons. © 1995 Wiley‐Liss, Inc.
Biochemical analysis of programmed cell death during premeiotic stages of spermatogenesis in vivo and in vitro
Authors: Callard Gloria V. , Jorgensen Joan C. , Redding J. Michael
Published: May 2005

Control points of regulator action during spermatogenesis are not completely known. Using the shark testis model, which facilitates analysis of spermatogenesis stage‐by‐stage in vivo and in vitro, an early biochemical marker of programmed cell death (PCD) was detected. Nucleosomal oligomers were seen in DNA extracts of testis and isolated spermatocysts (clonal germ cell/ Sertoli cell units) at premeiotic (PrM), but not meiotic (M) or postmeiotic (PoM), stages. Cell nuclei isolated from M stages of development were susceptible to cleavage by micrococcal nuclease, suggesting that developmental control of factors other than a nuclease‐insensitive chromatin structure may account for stage specificity. Cytological features of apoptosis were seen in germ cells, but not Sertoli cells, of a subset of isolated PrM spermatocysts and appeared to be all‐or‐none in affected clones. In culture, DNA fragmentation occurred on schedule with or without various additives, but the phosphodiesterase inhibitor 3‐isobutyl‐1‐methylxanthine (IBMX) decreased accumulation of DNA breakdown products. Identification of the apoptotic form of PCD as a major, variable component of normal spermatogenesis and the use of PrM spermatocysts as an in vitro test system will allow further definition of mechanisms and developmental and physiological controls. © 1995 Wiley‐Liss, Inc.
Cell interactions in testis development: Overexpression of c‐mos in spermatocytes leads to increased germ cell proliferation
Authors: Higgy Nadia A. , Zackson Saul L. , Van Der Hoorn Frans A.
Published: May 2005

Possible functions of the c‐mos proto‐oncogene during spermotogenesis were investigated through perturbations of its expression in transgenic mice. Two promoters, one from the pre‐meiotic male germ cell‐specific mouse phosphoglycerate kinase 2 gene, and the other from the post‐meiotic male germ cell‐specific rat RT7 gene were used to direct expression of c‐mos.

Northern blot analysis of testis RNA from transgenic PGK‐c‐mos mice indicated elevated levels of c‐mos RNA in spermatocytes and spermatids compared to controls. No transgene expression was detected in any other tissue examined, suggesting that the mouse PGK2 promoter, like the previously used human PGK2 promoter, confers correct cell‐specific expression onto c‐mos.

The promoter from a newly characterized rat gene, RT7, was shown to direct expression specific to post‐meiotic spermatids. Transgenic mice carrying an RT7‐lacZ construct displayed immunoreactive bacterial β‐galactosidase as well as enzyme activity in round spermatids. The cellular specificity for β‐galactosidase expression observed in RT7‐lacZ transgenic animals was in agreement with endogenous RT7 transcript expression. Northern blot analysis of testis RNA of RT7–c‐mos transgenic mice showed elevated levels of c‐mos in spermatids, but not in other cells or tissues examined.

Western blot analysis demonstrated elevated levels of p43c‐mos in spermatids of both PGK–c‐mos and RT7–c‐mos transgenic animals, but only PGK–c‐mos transgenics had increased p43cc‐mos levels in spermatocytes. Both RT7–c‐mos and PGK–c‐mos transgenic mice are fertile and show no tendency toward transformation. RT7–c‐mos mice have no discernible phenotype associated with the c‐mos overexpression in spermatids. However, PGK–c‐mos transgenic males exhibited a significant increase in germ cell number, as determined by cell counts using total germ cells and germ cells fractionated by centrifugal elutriation. Because mitotic divisions of germ cells occur prior to PGK–c‐mos transgene expression, our observations suggest that c‐mos overexpression in spermatocytes causes an alteration in cell–cell interactions. © 1995 Wiley‐Liss, Inc.
Identification of two positive transcriptional elements within the 91‐base pair promoter for mouse testis angiotensin converting enzyme (testis ACE)
Authors: Zhou Yudong , Delafontaine Patrick , Martin Brian M. , Bernstein Kenneth E.
Published: May 2005

Testis angiotensin‐converting enzyme (testis ACE) is an isozyme of ACE only expressed by male germ cells during spermiogenesis. It is the result of a strong sperm‐specific promoter found within the 12th intron of the somatic ACE gene. Previous studies have localized the boundaries of the mouse testis ACE promoter as being from −91 to −9, relative to the transcriptional start site, and have suggested two important DMA regulatory elements starting at positions −55 and −32. DNA constructs were made in which these motifs were either eliminated or substituted. Each construct was tested for its ability to promote transcription in vitro, using a rat testis nuclear extract. Disruption of either motif reduced in vitro transcription to about 30% of control levels, while mutations of both elements abolished transcription. Two sites were selected inside each motif and altered by point mutation. Each of four constructs, containing a mutation at −51, −48, −30, or −28, transcribed at 29% or less the efficiency of the parent construct. The DNA element at −55, TGAGGTCA, is homologous to a consensus cyclic AMP response element. The motif at −32, TCTTAT, is located at a position analogous to a TATA box. Substitution of the −32 motif with a consensus TATA box sequence, TATAAA, stimulated transcriptional activity about 3‐fold. As measured by gel mobility shift, oligonucleotides encompassing the −32 motif and the consensus TATA box formed different DNA‐protein complexes. However, the −32 motif oligonucleotide was recognized by nuclear proteins prepared from either liver or testis nuclei. In this example of a tissue‐specific promoter that functions only during spermatogenesis, at least two DNA elements act synergistically during in vitro transcription. © 1995 Wiley‐Liss, Inc.
Positive and negative feedback loops affect the transcription of IME1, a positive regulator of meiosis in Saccharomyces cerevisiae
Authors: Shefer‐Vaida Michal , Sherman Amir , Ashkenazi Tamar , Robzyk Kenneth , Kassir Yona
Published: May 2005

The IME1 gene of Saccharomyces cerevisiae encodes a transcription factor that is required for the expression of meiosis‐specific genes. Like many of the genes it regulates, IME1 itself is expressed according to the following complex pattern: barely detectable levels during vegetative growth, and high induced levels under starvation conditions, followed by a subsequent decline in the course of meiosis. This report examines the influence of Ime1 protein on its own expression, demonstrating feedback regulation. Disruption of either IME1 or IME2 leads to constantly increasing levels of Ime1‐lacZ expression, under meiotic conditions. This apparent negative regulation is due to cis elements in the IME1 upstream region, which confer transient meiotic expression to heterologous promoter‐less genes. A specific DNA/protein complex, whose level is transiently increased under meiotic conditions, is detected on this element. In ime1− diploids, the level of this DNA/protein complex increases, without any decline. These results indicate that the transient expression of IME1 is apparently due to transcriptional regulation. This report also presents evidence suggesting that Ime 1p is directly responsible for regulating its own transcription. Positive feedback regulation in mitotic conditions is suggested by the observation that overexpression of Ime 1p leads to increased levels of IME1‐lacZ. Negative autoregulation in meiotic cultures is demonstrated by the observation that a specific point mutation in IME1, ime 1–3, permits expression of meiosis‐specific genes, as well as induction of meiosis, but is defective in negative‐feedback regulation of IME1. © 1995 Wiley‐Liss, Inc.
Serum response element associated transcription factors in mouse embryos: Serum response factor, YY1, and PEA3 factor
Authors: Liu Shu‐Hui , Peng Bi‐Hung , Ma Jing‐Tyan , Liu Yin Chang , Ng Sun‐Yu
Published: May 2005

Many mammalian transcription factors, including human and mouse serum response factors (SRFs), are post‐translationally modified with O‐linked N‐acetylglucosamine monosaccharides on multiple serine and/or threonine residues. Nuclear extracts were prepared from 9.5 to 19 days postcoitum mouse embryos and subsequently were fractionated by wheat germ agglutinin (WGA)‐agarose affinity chromatography. SRF binds WGA‐agarose and apparently is O‐glycosylated. On the other hand, the low molecular weight serum response element (SRE)‐binding proteins, including the previously named band I and band II factors, did not bind WGA‐agarose. Furthermore, we showed that the fastest migrating complex contains the Yin‐Yang 1 (YY1) factor. YY1 binds to the c‐fos SRE and skeletal β‐actin muscle regulatory element (MRE), but not the cardiac β‐actin MRE. Nuclear extracts from NIH/3T3 fibroblasts contain similar, if not identical, SRE‐binding complexes. Besides these SRE‐binding factors, mouse PEA3‐binding factor, presumably an ETS domain‐containing protein, was found to bind SRF protein. This physical interaction, between SRF and ETS domain proteins, was shown to involve the DNA‐binding domain‐containing region of SRF and not the carboxyl‐terminal transactivation domain. © 1995 Wiley‐Liss, Inc.
Developmental variability of metallothionein Mtn gene expression in the species of the Drosophila melanogaster subgroup
Authors: Bonneton François , Wegnez Maurice
Published: May 2005

Developmental expression of the Drosophila melanogaster metallothionein Mtn gene has been analysed. Transcripts of this gene accumulate during the vitellogenic phase of oogenesis in a ring of follicular cells at the oocyte‐nurse cell margin and in the follicular cells surrounding the oocyte. There is also strong expression of the Mtn gene during the second half of embryogenesis in hemocytes, the endoderm midgut, and Malpighian tubules. A banded expression pattern is observed transiently in the midgut at stage 13. The two Mtn alleles, Mtn1 and Mtn.3, show quantitative differences in their expression patterns. Copper intoxication of flies does not induce ectopic expression of the Mtn gene, but rather leads to over‐expression of the gene in the structures where it is normally transcribed. Mtn transcription is not altered in homozygous mutants of four genes (lab, wg, dpp, bap) known to be involved in midgut morphogenesis.

Expression of Mtn has been also studied in six other species of the melanogaster subgroup. This analysis demonstrates that regulation of Mtn gene transcription has changed during evolution of the Drosophila lineage. For example, Mtn is expressed specifically in the Malpighian tubules of D. melanogaster while in D. mauritiana and D. sechellia the amnioserosa is a specific location of expression. Nonetheless, expression of Mtn in the midgut is common to the seven species, suggesting a basic role for the MTN protein during embryogenesis in this organ, possibly in the release of metallic ions from vitellogenins. In contrast, two genes also expressed in the embryonic midgut, lab and dFRA display identical patterns in all species of the melanogaster subgroup. The diversity of Mtn patterns in closely related Drosophila species exemplifies the rapid evolution of a gene regulatory system. © 1995 Wiley‐Liss, Inc.
Genetic mosaic analysis of the equatorial‐less mutation in Drosophila mezunogaster
Authors: Fryxell Karl J. , Wood C. Paige
Published: May 2005

eql (equatorial‐less) is a recessive lethal mutation on the second chromosome of Drosophila melanogasfer. J. Campos‐Ortega found that eql clones in somatic mosaic flies have reduced numbers of photoreceptor cells, and he suggested that only the R1, R6, and R7 photoreceptor cells were missing in this mutant. These photoreceptor cells help to define the inverted orientation of ommatidial facets along the equatorial midline of the fly eye, hence the mutation was named “equatorial‐less”. We have conducted a detailed analysis of the eql mutation, by serial section reconstruction of eql clones marked with bw or w− in somatic mosaic flies. We found that all photoreceptor cell types (Rl–R8) could be deleted by the eql mutation, and in rare cases the number of photoreceptor cells was increased. The apparent lack of photoreceptor cell type specificity was confirmed by our analysis of genetically mosaic facets, which indicated that no single photoreceptor cell, or subset of photoreceptor cells, was uniquely required to express eql Rather, eql appears to function in all photoreceptor cells, and possibly in all eye precursor cells. The distribution of photoreceptor cell numbers in w eql facets was consistent with the hypothesis that each photoreceptor cell was deleted independently of the others. The eql gene is located on the right arm of chromosome 2 at map location 2 − 104.5 ± 0.7 and lies between the polytene chromosome bands 59D8 and 60A7. © 1995 Wiley‐Liss, Inc.
Evaluation of an antisense RNA transgene for inhibiting growth hormone gene expression in transgenic rats
Authors: Matsumoto Kazuya , Kakidani Hitoshi , Anzai Masayuki , Nakagata Naomi , Takahashi Akio , Takahashi Yumi , Miyata Kenji
Published: May 2005

We compared the levels of growth hormone (GH) mRNA in the pituitary, plasma GH concentration, and altered phenotype in rats heterozygous and homozygous for an antisense RNA transgene targeted to the rat GH gene, with those in nontransgenic rats. We initially investigated whether the transgene promoter, which is connected to four copies of a thyroid hormone response element (TRE) that increases promoter activity, affected in vivo transgene expression in the pituitary of the transgenic rats. Plasma GH concentration correlated negatively with T, injection in surgically thyroidectomized heterozygous transgenic rats. There was a reduction of about ˜35–40% in GH mRNA levels in the pituitary of homozygous animals compared with those in non‐transgenic rats. Plasma GH concentration was significantly ˜25–32 and ˜29–41% lower in heterozygous and homozygous transgenic rats, respectively, compared with that in nontransgenic animals. Furthermore, the growth rates in homozygous transgenic rats were reduced by ˜72–81 and ˜51–70% compared with those of their heterozygous and nontransgenic littermates, respectively. The results of these studies suggested that the biological effect of GH in vivo is modulated dose‐dependently by the antisense RNA transgene. The rat GH gene can therefore be targeted by antisense RNA produced from a transgene, as reflected in the protein and RNA levels. © 1995 Wiley‐Liss, Inc.
Late embryo‐defective mutants of Arabidopsis
Authors: Vernon Daniel M. , Meinke David W.
Published: May 2005

The embryo‐defective (emb) mutants of Arabidopsis constitute a large and diverse group of mutants disrupted in a broad range of embryonic processes, including morphogonesis, cell differentiation, and maturation programs. This report describes a subset of these mutants, the late embryo defectives, which develop beyond the globular stage of embryogenesis but fail to complete normal morphogenesis. A representative sample of 12 late mutants was chosen for this study, patterns of morphogenesis were characterized, the germination potential of mutant seeds was investigated, and additional mutant alleles within the collection were identified. Morphological defects in mutant embryos became apparent during the heart stage of development, when embryos normally begin the rapid cell division and expansion required for the completion of morphogenesis. Despite their morphological abnormalities, mutant embryos often germinated from dry seed, demonstrating that genetic programs required for the establishment of desiccation tolerance remained intact. Mutant seedlings displayed a wide range of developmental abnormalities, including altered morphology, lack of pigmentation, dwarfism, and disorganized vegetative growth. One late mutant was found to be allelic to an early embryo defective that arrests at the globular stage. These results suggest that a number of late EMB genes encode basic cellular and metabolic functions needed for cell division, enlargement, and embryonic growth. The rapid growth and metabolic changes that occur at the heart stage may present a barrier to normal development in the late mutants, resulting in altered embryo morphology and other developmental defects. It is proposed that many Arabidopsis mutants with abnormal embryo and seedling morphology are not defective in the regulation of pattern formation or morphogenesis, but rather in fundamental physiological and cellular processes required for the completion of normal growth and development. © 1995 Wiley‐Liss, Inc.
cyd, a mutant of pea that alters embryo morphology is defective in cytokinesis
Authors: Liu Chun‐Ming , Johnson Sue , Wang Trevor L.
Published: May 2005

Embryogenesis in higher plants requires the precise regulation of cell division, orientation of cell elongation and specification of cell differentiation. The division plane is determined by the position of a new cell plate at cytokinesis. A mutant of pea has been isolated in which both the embryo pattern and surface morphology is altered. The phenotype of the mutant is manifest primarily in the cotyledons where cell plates only partially form, generating cell wall stubs and multinucleate cells. Some cotyledonary cells of the mutant proceed through nine DNA replication cycles, including nuclear division, but not cytokinesis, producing nuclei with a DNA content of ca. 1000C. The cytological phenotype of the mutant could be mimicked by the treatment of wild‐type cells with caffeine. We have termed this mutant cytokinesis‐defective (cyd). © 1995 Wiley‐Liss, Inc.
Transcription of the Zea mays homeobox (ZmHox) genes is activated early in embryogenesis and restricted to meristems of the maize plant
Authors: Klinge Bettina , Werr Wolfgang
Published: May 2005

Four Zea mays homeobox (ZmHox) genes have been analyzed in their spatial expression pattern during development of the maize plant. The ZmHox1a or b and ZmHox2a or b gene pairs encode putative plant transcriptin factors; the mRNA transcripts belong to the rare class of mRNA molecules. Expression of the ZmHox1 and 2 genes is activated very early in embryonic development and restricted to the embryo proper in the proembryo stage. After establishment of the root/shoot axis, transcripts are prevalent in the embryonic root and shoot apical meristems but later are also found in provascular tissues and young leaf primordia. In the vegetative plant body the transcription of the ZmHox genes marks several types of meristems of the shoot and root system, the descending proliferating regions and provascular strands. Expression persists in the developing reproductive organs, but results obtained in the male flower indicate that transcription of ZmHox genes here may become confined to specific cell types. The data obtained during this study show that these four ZmHox genes are expressed very specifically in cells where developmental decisions contribute to the ontogeny of the maize plant. The overall expression pattern suggests that the ZmHox class of maize homeobox genes will be involved in transcriptional control during maize development from the embryonic to the reproductive phase. © 1995 Wiley‐Liss, Inc.
Effect of mutations in the PINHEAD gene of Arabidopsis on the formation of shoot apical meristems
Authors: McConnell Jane R. , Barton M. Kathryn
Published: May 2005

The primary shoot apical meristem of angiosperm plants is formed during embryogenesis. Lateral shoot apical meristems arise postembryonically in the axils of leaves. Recessive mutations at the PINHEAD locus of Arabidopsis interfere with the ability of both the primary shoot apical meristem as well as lateral shoot apical meristems to form. However, adventitious shoot apical meristems can form in pinhead mutant seedlings from the axils of the cotyledons and also from cultred root explants. In this report, the phenotype of pinhead mutants is described, and a hypothesis for the role of the wild‐type PINHEAD gene product in shoot meristem initiation is presented. © 1995 Wiley‐Liss, Inc.