bluuebunny/crossref_metadata_2025_split huggingface dataset:
Temperature‐dependent sex determination in reptiles: Proximate mechanisms, ultimate outcomes, and practical applications
Authors: Crews David , Bergeron Judith M. , Bull James J. , Flores Deborah , Tousignant Alan , Skipper James K. , Wibbels Thane 
Published: May 2005

AbstractIn many egg‐laying reptiles, the incubation temperature of the egg determines the sex of the offspring, a process known as temperature‐dependent sex determination (TSD). In TSD sex determination is an “all or none” process and intersexes are rarely formed. How is the external signal of temperature transduced into a genetic signal that determines gonadal sex and channels sexual development? Studies with the red‐eared slider turtle have focused on the physiological, biochemical, and molecular cascades initiated by the temperature signal. Both male and female development are active processes—rather than the crganized/default system characteristic of vertebrates with genotypic sex determination—that require simultaneous activation and suppression of testis‐ and ovary‐determining cascades for normal sex determination. It appears that temperature accomplishes this end by acting on genes encoaing for steroidogenic enzymes and steroid hormone receptors and modifying the endocrine microenvironment in the embryo. The temperature experienced in development also has long‐term functional outcomes in addition to sex determination. Research with the leopard gecko indicates that incubation temperature as well as steroid hormones serve as organizers in shaping the adult phenotype, with temperature modulating sex hormone action in sexual differentiation. Finally, practical applications of this research have emerged for the conservation and restoration of endangered egg‐laying reptiles as well as the embryonic development of reptiles as biomarkers to monitor the estrogenic effects of common environmental contaminants. © 1994 Wiley‐Liss, Inc.
S6 phosphorylation results from prothoracicotropic hormone stimulation of insect prothoracic glands: A role for S6 kinase
Authors: Song Qisheng , Gilbert Lawrence I. 
Published: May 2005

AbstractThe insect prothoracic glands are the source of steroidal molting hormone precursors and the glands are stimulated by a brain neuropeptide, prothoracicotropic hormone (PTTH). Previous work from this laboratory revealed that PTTH acts via a cascade including Ca2+/calmodulin activation of adenylate cyclase, protein kinase A, and the subsequent phosphorylation of a 34 kDa protein (p34) hypothesized, but not proven, to be the 56 protein of the 40S ribosomal subunit. The jmmunosuppressive macrolide, rapamycin, is a potent inhibitor of cell proliferation, a signal transduction blocker, and also prevents ribosomal S6 phosphorylation in mammalian systems. We demonstrate here that rapamycin inhibited PTTH‐stimulated ecdysteroidogenesis in vitro by the prothoracic glands of the tobacco hornworm, Manduca sexta, with half‐maximal inhibition at a concentration of about 5 nM. At concentrations above 5 nM, there was a 75% inhibition of ecdysteroid biosynthesis. Similar results, were observed with the calcium ionophore (A23187), a known stimulator of ecdysteroidogenesis. Most importantly, the inhibition of ecdysteroid biosynthesis was accompanied by the specific inhibition of the phosphorylation of p34, indicating that p34 indeed is ribosomal protein S6. In vivo assays revealed that injection of rapamycin into day 6 fifth instar larvae resulted in a decreased hemolymph ecdysteroid titer and a dose‐dependent delay in molting and metamor‐phosis. When S6 kinase (S6K) activity was examined using rapamycin‐treated prothoracic glands as the enzyme source and a synthetic peptide (S6‐21) or a 40S ribosomal subunit fraction from Manduca tissues as substrate, the date revealed that rapamycin inhibited S6K activity. The composite data suggest that rapamycin inhibits a signal transduction element leading to p34 phosphorylation that is necessary for PTTH‐stimulated ecdysteroidogenesis in this insect endocrine gland, and lend further support to the concept that p34 is S6. © 1994 Wiley‐Liss, Inc.
Cloning of a thyroid hormone‐responsive Rana catesbeiana c‐erbA‐β gene
Authors: Davey Jennifer C. , Schneider Mark J. , Galton Valerie Anne 
Published: May 2005

AbstractTwo types of thyroid hormone receptor (c‐erbA) gene have been identified in mammals and in lower species including chickens and the amphibian Xenopus laevis. The two genes are located on different chromosomes and have been named TRα and TRβ We have described previously the cloning of a TRβ cDNA from Rana catesbeiana (RC) tissues (RC15) and we now report the cloning of a TRβ cDNA from this species. The cloning strategy employed utilized the polymerase chain reaction (PCR), with primers based on the sequences of the X. laevis TRβ cDNA (XenTRβ) and an RCTRβ genomic clone, which, by analogy with XenTRβ, contains some of the 3′ end of the open reading frame together with 3′‐untranslated sequences. At the nucleotide and amino acid levels, respectively, the cloned RCTRβ cDNA is 90% and 98% homologous with XenTRβ, and 72% and 76% homologous with RC15. Following in vitro transcription and translation, the cDNA was shown to encode a 48 kilodalton protein which binds 3,5, 3′‐triiodothyronine (T3) with high affinity (mean Kd: 0.032 nM). Samples of total or poly(A)+RNA from tadpoles at different stages of metamorphosis and from adult frogs were analyzed for the presence ofTRβ‐specific transcripts by slot blot analysis using as probe a 258 bp section of the RCTRβ cDNA. This section of the cDNA does not hybridize to the corresponding section of RC15. In confirmation of previous findings, β‐specific transcripts were not detected in RNA from tadpole red blood cells (RBCs) and none was found in RBCs from adult frogs. However, β‐specific transcripts were detected in RNA from tail, skin, and liver of stage XIII tadpoles, and the levels were greatly increased in these tissues during metamorphic climax. In the adult frog, the level was minimal in all tissues studied. In other studies using stage XII tadpoles and a reverse transcription‐polymerase chain reaction assay, β‐specific transcripts were readily detected in tail, skin, kidney, leg, heart, intestine, and eye but minimal or absent in liver, brain, and RBCs. Within 2 days of injection of T3, the level of β‐specific transcripts was markedly increased in all tissues. These findings strongly suggest that the expression of the RCTRβ gene is regulated developmentally and/or by thyroid hormone in most tissues of the RC tadpole. © 1994 Wiley‐Liss, Inc.
Upregulation of AP‐2 in the skin of Xenopus laevis during thyroid hormone‐induced metamorphosis
Authors: French Randall P. , Warshawsky David , Tybor Lisa , Mylniczenko Natalie D. , Miller Leo 
Published: May 2005

AbstractDuring amphibian metamorphosis dramatic changes occur in the morphogenesis and differentiation of the epidermis. Concurrently with these changes, the 63 kDa keratin geneis upregulated from low basal levels to high levels. What makes these processes unique is that they are controlled by triiodothyronine (T3) and can be duplicated in cultures of purified epidermal cells. Since there is a 2 day lag period between the addition of T3 and the upregulation of keratin gene expression and terminal differentiation, recent studies have focused on identifying the genes activated during the lag period. We assume that the transcription factors required for upregulation of the keratin gene are induced by T3 during the lag period, and therefore we have cloned the keratin gene so that promoter analyses can be conducted. S1 mapping assays have shown that the same transcription start sites are used during premetamorphosis when the keratin gene is basally expressed, during metamorphosis when it is T3‐upregulated, and in the adult epidermis where it is expressed independently of T3. During the early part of the lag period TRP and AP‐2 mRNA levels are upregulated in the epidermis by T3. The transcription factor AP‐2 is expressed at high levels in the skin of premetamorphic larvae and induced about fivefold by T3 but is not induced in an epithelial cell line (XL‐177). Since the keratin mRNA, AP‐2 rnRNA, and other genes induced during the lag period are expressed in premetamorphic larvae it appears that T3 functions by upregulating the expression of genes previously activated by a T3‐independent process. This preprogramming may account for the tissue specificity of T3 action during metamorphosis. © 1994 WiIey. Liss, Inc.
frizzled Gene expression and development of tissue polarity in the Drosophila wing
Authors: Park Woo Jin , Liu Jingchun , Adler Paul N. 
Published: May 2005

AbstractAlmost every cell in the Drosophila pupal wing forms a single, distally pointing cuticular hair. The function of the frizzled (fz) gene is essential for the elaboration of the normal wing hair pattern. In the absence of fz function hairs develop, but they display an abnormal polarity. We have examined the developmental expression of the fi gene at the RNA level via in situ hybridization and at the protein level via Western blotting. We have found that fz is expressed in all regions of the epidermis before, during, and after the fz cold sensitive period. We have also found that fz function is not required for normal fi expression. We have further found that mutations in several other tissue polarity genes do not noticeably alter the expression or the modification state of the Fz protein. © 1994 Wiley‐Liss, Inc.
TheKnottedleaf blade is a mosaic of blade, sheath, and auricle identities
Authors: Sinha Neelima , Hake Sarah 
Published: May 2005

AbstractThe dominantKnotted‐1mutations in maize alter development of the leaf blade. Sporadic patches of localized growth, or knots, and fringes of ectopic ligule occur along lateral veins of mutant leaf blades. In addition, bundle sheaths do not completely encircle lateral veins on mutant leaf blades. We have compared mutant leaf blades with wild‐type leaves to determine the precise nature of the perturbed regions. Our analysis includes characterization of epidermal cell shapes, localization of photosynthetic proteins and histology of the leaf. We show that mutant leaf blades are a mosaic of leaf organ components. Affected regions of mutant leaf blades resemble either sheath or auricle tissue in both external and internal features. This conversion of blade cells represents an acropetal shift of more basal parts of the leaf blade region and correlates with previously identified ectopic expression of theKnotted‐1protein in the leaf blade. We propose that inappropriate expression ofKn1interferes with the process of establishment of cell identities, resulting in early termination of the normal blade development program or precocious expression of the sheath and auricle development programs. © 1994 Wiley‐Liss, Inc.
Epigenetic effects in eukaryotic gene expression
Authors: Bestor Timothy H. , Chandler Vicki L. , Feinberg Andrew P. 
Published: May 2005

AbstractIn the broadest terms, epigenetic phenomena in eukaryotes depend on the interaction of alleles or repeated sequences or on the mitotic inheritance of chromatin states or methylation patterns. One of the most exciting aspects of the study of epigenetic phenomena is the insight that can be gained into the structure and assembly of higher‐order chromatin structures, an important subject that has proved refractory to current biochemical methodologies. Rapid progress in the study of gene inactivation in fungi, plants, and invertebrates will provide new hypotheses to be tested in mammals. © 1994 Wiley‐Liss, Inc.
Spreading the silence: Epigenetic transcriptional regulation during Drosophila development
Authors: Moehrle Axel , Paro Renato 
Published: May 2005

AbstractIn early Drosophila development a complex cascade of diffusible transcription factors generates an intricate expression pattern of developmental regulators such as the homeotic genes. The mechanism which subsequently maintains the pattern during the rest of development is mainly using epigenetic features for its function. Evidence comes from the analysis of the Polycomb‐group (Pc‐G), a class of genes which is responsible for maintaining the inactive state of expression. The Pc‐G was found to share many parallels to genes involved in heterochromatin formation. Different members of the Pc‐G interact in large multiprotein complexes, which apparently can cover and inactivate large chromosomal domains. Specific DNA elements have been identified that are used by the Pc‐G proteins to nucleate these specialized domains of silent chromatin. Thus, the Pc‐G proteins appear to permanently inactivate genes by generating heterochromatin‐like structures which could then be inherited by the daughter cells in an epigenetic manner. Heritable gene silencing is an important but little understood mechanism in pattern formation. Phenomenologically related effects have been observed in many organisms. These range from the transcriptional silencing of the inactive mating type loci in yeast to parental imprinting phenomena and X‐chromosome inactivation in mammals. Analysis of these functions in Drosophila provides an excellent model system for studying the molecular basis of such epigenetic mechanisms that use higher order chromatin structures for transcriptional repression. © 1994 Wiley‐Liss, Inc.
Positional information and pattern formation in development
Authors: Wolpert L. 
Published: May 2005

AbstractA widely used mechanism for pattern formation is based on positional information: cells acquire positional identities as in a coordinate system and then interpret this information according to their genetic constitution and developmental history. In Drosophila maternal factors establish the axes and set up a maternal system of positional information on which further patterning is built. There is a cascade of gene activity which leads both to the development of periodic structures, the segments, and to their acquiring a unique identity. This involves the binding of transcription factors to regulatory regions of genes to produce sharp thresholds. Many of the genes involved in these processes, particularly the Hox complex, are also involved in specifying the body axis and limbs of vertebrates. There are striking similarities in the mechanisms for spcifying and recording positional identity in Drosophila and vertebrates. © 1994 Wiley‐Liss, Inc.
Developmental significance of epigenetic impositions on the plant genome: A paragenetic function for chromosomes
Authors: Jorgensen Richard 
Published: May 2005

AbstractDevelopmental and physiological factors can impose heritable metastable changes on the plant genome, a fact that was established by maize geneticists during the 1950s and 1960s, largely through the efforts of R. Alexander Brink and Barbara McClintock. This paper describes a transgenic reporter system that monitors genomic impositions as changes in morphogenetically‐determined flower color patterns. The observations reported here on the metastable properties of plant transgenes illustrate the proposals of Brink and McClintock that chromosomal impositions occur during normal development as ordered sequences of events which contribute to the elaboration of complex developmental patterns. The relationship between this process and some recent findings about the control of gene expression in transgenic plants is also discussed. © 1994 Wiley‐Liss, Inc.
Tumor suppression in Drosophila is causally related to the function of the lethal(2)tumorous imaginal discs gene, a dnaJ homolog
Authors: Kurzik‐Dumke Ursula , Gundacker Dietmar , Rentrop Martin , Gateff Elisabeth 
Published: May 2005

AbstractThe Drosophila melanogaster tumor suppressor gene lethal(2)tumorous imaginal discs (l(2)tid) causes in homozygotes malignant growth of cells of the imaginal discs and the death of the mutant larvae at the time of puparium formation. We describe the molecular cloning of the 1(2)tid+ gene and its temporal expression pattern in the wild‐type and mutant alleles. Germ line rescue of the tumor phenotype was achieved with a 7.0 kb Hindlll‐fragment derived from the polytene chromosome band 59F5. The l(2)tid+ gene spans approximately 2.5 kb of genomic DNA. The protein coding region, 1,696 bps long, is divided by an intron into two exons. The predicted Tid56 protein contains 518 amino acids and possesses a theoretical molecular weight of 56 kDa. It shows significant homology to all known DnaJ related proteins from bacteria, yeast, and man. The possible function of the Tid56 protein in tumor suppression is delineated. © 1995 Wiley‐Liss, Inc.
Epidermal cell‐specific quantitation of dopa decarboxylase mRNA in Drosophila by competitive RT‐PCR: An effect of Broad‐Complex mutants
Authors: O'Keefe Sandra , Schouls Michelle , Hodgetts Ross 
Published: May 2005

AbstractThe quontitation of RNA in tissue homogenates by amplifying the product of reverse transcription (RT‐PCR) is sufficiently sensitive to detect molecules in the range of 10−110−2 amole. We describe here the steps we believe necessary to validate a protocal that used a DNA competitor and visualization of the amplification products by ethidium bromide staining. The procedure was designed to quantitate one of the tissue specific transcripts of the Dopa decarboxylase gene (Ddc) in Drosophila. We demonstrate that the amount of epidermal Ddc transcript is much lower at pupariation in several mutants of the Broad‐Complex, one of the primary response loci of the moulting hormone, ecdysone. The mutant effects were allele specific and the molecular basis of one of these alleles is known. This implicates a particular family of the zinc finger proteins encoded by the locus in the hormone dependent induction of Ddc expression.
Germ cell‐sertoli cell interactions: Regulation by germ cells of the stage‐specific expression of CP‐2/cathepsin LmRNA by sertoli cells
Authors: Wright William W. , Zabludoff Sonya D. , Penttilä Tarja‐Leena , Parvinen Martti 
Published: May 2005

AbstractCP‐2/cathepsin LmRNA is expressed primarily by rat Sertoli cells within stage VI–VIII seminiferous tubules. To test whether germ cells regulated this expression, we examined if separating Sertoli cells from specific germ cells affected expression of this transcript in Sertoli cells. First, Sertoli cells were isolated from adult (90‐day‐old) and immature (25‐day‐old) rats and levels of this transcript measured immediately or after 1, 3 and 5 days in culture. Results demonstrated that immediately upon isolation, CP‐2/cathepsin LmRNA levels were significantly higher in mature cells. However, after 1 day in culture, the levels of this transcript increased in immature cells and remained high in mature cells. We therefore conclude that in vivo, a subset of germ cells inhibit the expression of CP‐2/cathepsin LmRNA by immature Sertoli cells. Second, to examine the effect of specific germ cells on CP‐2/cathepsin LmRNA expression, we exposed the testes of mature rats to 3 Gy of γ‐radiation and analyzed stage‐specific expression of this transcript at varying times during maturation depletion and subsequent germ cell restoration. Loss of spermatogonia or spermatocytes was without effect. However, when pachytene spermatocytes through step 14 spermatids were depleted, expression at stages VI–VIII was reduced by half and expression at stages IX‐I was increased 14‐fold. These changes resulted in the loss of stage‐specific expression of CP‐2/cathepsin LmRNA by Sertoli cells. Finally, stage VI–VIII tubules, depleted primarily in step 15–19 spermatids, had levels of CP‐2/cathepsin LmRNA that were 60% of control. However, stage‐specific expression of this transcriot was detected in these tubules. In contrast to whai we noted with CP‐2/cathepsin LmRNA, loss and restoration of germ cells had no effect on Sertoli cell levels of SGP‐2 mRNA, indicating that testicular irradiation had no Overall effect on Sertoli cell function Taken togetherr these data suggest that the stage‐specific expression of the CP‐2/ cathepsin L gene results from the sequential stimulation and inhibition of Sertoli cells by germ cells, that pachytene spermatocytes through step 14 spermatids are required for this stage‐specific expression and that step 18 and 19 spermatids amplify this expression at stages VI–VIII. © 1995 Wiley‐Liss, Inc.
Transcriptional regulation of Sertoli cell differentiation (transferrin promoter activation) during testicular development
Authors: Chaudhary Jaideep , Skinner Michael K. 
Published: May 2005

AbstractPreviously testicular peritubular cells have been shown to produce a paracrine factor PModS that promotes Sertoli cell differentiation. This mesenchymal‐epithelial cell interaction appears to regulate a number of Sertoli cell differentiated functions including transferrin gene expression. The current study was designed to identify PModS‐activated response elements in the transferrin promoter and correlate this with Sertoli cell differentiation that occurs during testis development. The 3‐kb transferrin promoter was digested down to approximately 200‐bp fragments. Nuclear extracts from Sertoli cells stimulated with PModS were used in gel mobility shift assays. Two promoter regions located at −2.4 kb and −1.9 kb were designated SE1 and SE2. PModS promoted the presence of factors in Sertoli cell nuclear extracts that bind SE1 and SE2. Displacement studies demonstrated that SE1 and SE2 are distinct. A transferrin promoter‐reporter construct containing these apparent response elements was activated by PModS, while a minimal transferrin promoter of 600bp excluding SE1 and SE2 was only partially stimulated by PModS. Therefore, PModS appears to in part activate the transferrin promoter through SE1 and/or SE2. Gel shift assays with Sertoli cell nuclear extracts and 20‐day‐old testis extracts were the same. Interestingly, the nuclear extract from a new‐born testis also had a gel shift. Therefore, some of the nuclear factors stimulated by PModS in Sertoli cells and present in mid‐pubertal testis were also present at birth upon completion of embryonic development. Previously transferrin expression has been shown to increase significantly at the onset of puberty. Observations indicate that PModS appears to in part promote transferrin expression through two newly identified response elements designated SE1 and SE2 and that the nuclear factors that bind these elements are present after embryonic development and mid‐pubertally. © 1995 Wiley‐Liss, Inc.
A haploid and a diploid cell cycle coexist in an in vitro immortalized spermatogenic cell line
Authors: Hofmann Marie‐Claude , Abramian Donara , Millán José Luis 
Published: May 2005

AbstractWe have recently established a conditionally immortalized germ cell line [GC‐2spd(ts)] that, at the permissive temperatures of 37°C and 32°C, is able to undergo meiosis in vitro and form round spermatids [Hofmann et al., (1994): Proc Natl Acad Sci USA 91:5533–5537]. In this report, we provide data that indicate that the GC‐2spd(ts) cell line consists of two cell populations undergoing a haploid (n/2n) cell cycle and a diploid (2n/4n) cell cycle, respectively. The cells containing 2n DNA, when sorted by fluorescence‐activated cell sorting, are able to reconstitute the full population of n/2n/4n DNA cells, indicating that they are able to commit to the reductive meiotic division and form haploid spermatids or to continue self‐replication through a diploid cell cycle. This GC‐2spd(ts) cell line provides a valuable tool to study the molecular mechanisms involved in the cellular decision between self‐renewal by mitosis and commitment to meiosis. © 1995 Wiley‐Liss, Inc.