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11.
Evolution of the 28S ribosomal RNA gene in anurans: regions of variability and their phylogenetic implications 总被引:1,自引:0,他引:1
Fifteen restriction sites were mapped to the 28S ribosomal RNA gene of
individuals representing 54 species of frogs, two species of salamanders, a
caecilian, and a lungfish. Eight of these sites were present in all species
examined, and two were found in all but one species. Alignment of these
conserved restriction sites revealed, among anuran 28S rRNA genes, five
regions of major length variation that correspond to four of 12 previously
identified divergent domains of this gene. One of the divergent domains
(DD8) consists of two regions of length variation separated by a short
segment that is conserved at least throughout tetrapods. Most of the
insertions, deletions, and restriction-site variations identified in the
28S gene will require sequence-level analysis for a detailed reconstruction
of their history. However, an insertion in DD9 that is coextensive with
frogs in the suborder Neobatrachia, a BstEII site that is limited to
representatives of two leptodactylid subfamilies, and a deletion in DD10
that is found only in three ranoid genera are probably synapomorphies.
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Allophanate lyase can be induced by urea or acetamide 20-40-fold within 4 h in NH4 + -deprived cultures of Chlamydomonas reinhardi. In light-synchronized cultures, allophanate lyase induction appeared to be limited to the light phase of the cell cycle, provided that culture samples were induced under ongoing illumination conditions (i.e. light induction of light phase cells and dark induction of dark phase cells). However, when culture samples were induced under constant light conditions this cell cycle pattern was abolished. Light was found to be required for allophanate lyase induction and this was shown to be due, in part, to the light requirement for inducer uptake. The relationship between allophanate lyase induction and gametogenesis is discussed. 相似文献
14.
The murid rodent subfamily Sigmodontinae contains 79 genera which are
distributed throughout the New World. The time of arrival of the first
sigmodontines in South America and the estimated divergence time(s) of the
different lineages of South American sigmodontines have been controversial
due to the lack of a good fossil record and the immense number of extant
species. The "early-arrival hypothesis" states that the sigmodontines must
have arrived in South America no later than the early Miocene, at least 20
MYA, in order to account for their vast present-day diversity, whereas the
"late-arrival hypothesis" includes the sigmodontines as part of the
Plio-Pleistocene Great American Interchange, which occurred approximately
3.5 MYA. The phylogenetic relationships among 33 of these genera were
reconstructed using mitochondrial DNA (mtDNA) sequence data from the ND3,
ND4L, arginine tRNA, and ND4 genes, which we show to be evolving at the
same rate. A molecular clock was calibrated for these genes using published
fossil dates, and the genetic distances were estimated from the DNA
sequences in this study. The molecular clock was used to estimate the dates
of the South American sigmodontine origin and the main sigmodontine
radiation in order to evaluate the "early-" and "late-arrival" scenarios.
We estimate the time of the sigmodontine invasion of South America as
between approximately 5 and 9 MYA, supporting neither of the scenarios but
suggesting two possible models in which the invading lineage was either (1)
ancestral to the oryzomyines, akodonts, and phyllotines or (2) ancestral to
the akodonts and phyllotines and accompanied by the oryzomyines. The
sigmodontine invasion of South America provides an example of the advantage
afforded to a lineage by the fortuitous invasion of a previously
unexploited habitat, in this case an entire continent.
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15.
Escargot maintains stemness and suppresses differentiation in Drosophila intestinal stem cells 下载免费PDF全文
16.
Over the past few years, secure and privacy-preserving user authentication scheme has become an integral part of the applications of the healthcare systems. Recently, Wen has designed an improved user authentication system over the Lee et al.’s scheme for integrated electronic patient record (EPR) information system, which has been analyzed in this study. We have found that Wen’s scheme still has the following inefficiencies: (1) the correctness of identity and password are not verified during the login and password change phases; (2) it is vulnerable to impersonation attack and privileged-insider attack; (3) it is designed without the revocation of lost/stolen smart card; (4) the explicit key confirmation and the no key control properties are absent, and (5) user cannot update his/her password without the help of server and secure channel. Then we aimed to propose an enhanced two-factor user authentication system based on the intractable assumption of the quadratic residue problem (QRP) in the multiplicative group. Our scheme bears more securities and functionalities than other schemes found in the literature. 相似文献
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Proliferating cell nuclear antigen (PCNA) as a proliferative marker during embryonic and adult zebrafish hematopoiesis 总被引:3,自引:1,他引:3
Leung AY Leung JC Chan LY Ma ES Kwan TT Lai KN Meng A Liang R 《Histochemistry and cell biology》2005,124(2):105-111
We investigated the expression of proliferative cell nuclear antigen (PCNA) in zebrafish to delineate the proliferative hematopoietic
component during adult and embryonic hematopoiesis. Immunostaining for PCNA and enhanced green fluorescence protein (eGFP)
was performed in wild-type and fli1-eGFP (endothelial marker) and gata1-eGFP (erythroid cell marker) transgenic fish. Expression
of PCNA mRNA was examined in wild-type and chordin morphant embryos. In adult zebrafish kidney, the renal tubules are surrounded
by endothelial cells and it is separated into hematopoietic and excretory compartments. PCNA was expressed in hematopoietic
progenitor cells but not in mature neutrophils, eosinophils or erythroid cells. Some PCNA+ cells are scattered in the hematopoietic
compartment of the kidney while others are closely associated with renal tubular cells. PCNA was also expressed in spermatogonial
stem cells and intestine crypts, consistent with its role in cell proliferation and DNA synthesis. In embryos, PCNA is expressed
in the brain, spinal cord and intermediate cell mass (ICM) at 24 h-post fertilization. In chordin morphants, PCNA is significantly
upregulated in the expanded ICM. Therefore, PCNA can be used to mark cell proliferation in zebrafish hematopoietic tissues
and to identify a population of progenitor cells whose significance would have to be further investigated. 相似文献
19.
J. Purkayastha T. Sugla A. Paul S. K. Solleti P. Mazumdar A. Basu A. Mohommad Z. Ahmed L. Sahoo 《Biologia Plantarum》2010,54(1):13-20
An efficient and reproducible in vitro plant regeneration system from shoot apices was developed in Jatropha curcas. Benzylaminopurine (BAP; 2.5 μM) was most effective in inducing an average of 6.2 shoots per shoot apex. Incorporation of gibberellic acid (GA3; 0.5 μM) to basal medium was found essential for elongation of shoots. The BAP-habituated mother explants continuously produced shoots during successive subculture without any loss of morphogenic potential. The shoots rooted efficiently on half-strength MS medium. The rooted plantlets were acclimatized with more than 98 % success and the plants transferred to soil:compost in nursery showed no sign of variation compared to the seed-grown plants. The whole process of culture initiation to plant establishment was accomplished within 5–6 weeks. A genetic transformation system in J. curcas was established for the first time, using bombardment of particles coated with plasmid pBI426 with a GUS-NPT II fusion protein under the control of a double 35S cauliflower mosaic virus (CaMV) promoter. The β-glucuronidase (GUS) activity in J. curcas shoot apices was significantly affected by the gold particle size, bombardment pressure, target distance, macrocarrier travel distance, number of bombardments, and type and duration of osmotic pre-treatment. The proliferating bombarded shoot apices were screened on medium supplemented with 25 mg dm−3 kanamycin and surviving shoots were rooted on medium devoid of kanamycin. The integration of the transgene into genomic DNA of transgenic plants was confirmed by PCR and Southern blot hybridization. The transgenic plants showed insertion of single to multiple copies of the transgene. 相似文献
20.
A critical step in the development of robust Agrobacterium tumefaciens-mediated transformation system in recalcitrant grain legume, cowpea is the establishment of optimal conditions for efficient T-DNA delivery into target tissue and recovery of transgenic plants. A dramatic increase in efficiency of T-DNA delivery was achieved by constitutive expression of additional vir genes in resident pSB1 vector in Agrobacterium strain LBA4404. A geneticin based selection system permitted rapid and efficient identification of transgenic shoots without interfering with their regeneration, and eliminated the bulk of escapes. Supplementation of 0.5 μM kinetin to medium containing 5.0 μM benzyl aminopurine after 1 week of culture followed by 3 weeks of culture were found critical for optimal multiplication and elongation of transformed shoots from cotyledonary node explants. Combining these three developments, we recovered fertile transgenic plants at a frequency of 1.64%, significantly higher than previous reports. The presence, integration, expression and inheritance of transgenes were confirmed by molecular analysis. The protocol developed for cultivar Pusa Komal will facilitate the transfer of desirable traits into cowpea. 相似文献