Human infectivity trait in <i>Trypanosoma brucei</i>: stability, heritability and relationship to sra expression

Some Trypanosoma brucei lines infect humans whereas others do not because the parasites are lysed by human serum. We have developed a robust, quantitative in vitro assay based on differential uptake of fluorescent dyes by live and dead trypanosomes to quantify the extent and kinetics of killing by human serum. This method has been used to discriminate between 3 classes of human serum resistance; sensitive, resistant and intermediate. TREU 927/4, the parasite used for the T. brucei genome project, is intermediate. The phenotype is expressed in both bloodstream and metacyclic forms, is stably expressed during chromic infections and on cyclical transmission through tsetse flies. Trypanosomes of intermediate phenotype are distinguished from sensitive populations of cells by the slower rate of lysis and by the potential to become fully resistant to killing by human serum as a result of selection or long-term serial passaging in mice, and to pass on full resistance phenotype to its progeny in a genetic cross. The sra gene has been shown previously to determine human serum resistance in T. brucei but screening for the presence and expression of this gene indicated that it is not responsible for the human serum resistance phenotype in the trypanosome lines that we have examined, indicating that an alternative mechanism for HSR exists in these stocks. Examination of the inheritance of the phenotype in F1 hybrids for both bloodstream and metacyclic stages from 2 genetic crosses demonstrated that the phenotype is co-inherited in both life-cycle stages in a manner consistent with being a Mendelian trait, determined by only one or a few genes

The role of LINEs and CpG islands in dosage compensation on the chicken Z chromosome

Most avian Z genes are expressed more highly in ZZ males than ZW females, suggesting that chromosome-wide mechanisms of dosage compensation have not evolved. Nevertheless, a small percentage of Z genes are expressed at similar levels in males and females, an indication that a yet unidentified mechanism compensates for the sex difference in copy number. Primary DNA sequences are thought to have a role in determining chromosome gene inactivation status on the mammalian X chromosome. However, it is currently unknown whether primary DNA sequences also mediate chicken Z gene compensation status. Using a combination of chicken DNA sequences and Z gene compensation profiles of 310 genes, we explored the relationship between Z gene compensation status and primary DNA sequence features. Statistical analysis of different Z chromosomal features revealed that long interspersed nuclear elements (LINEs) and CpG islands are enriched on the Z chromosome compared with 329 other DNA features. Linear support vector machine (SVM) classifiers, using primary DNA sequences, correctly predict the Z compensation status for >60% of all Z-linked genes. CpG islands appear to be the most accurate classifier and alone can correctly predict compensation of 63% of Z genes. We also show that LINE CR1 elements are enriched 2.7-fold on the chicken Z chromosome compared with autosomes and that chicken chromosomal length is highly correlated with percentage LINE content. However, the position of LINE elements is not significantly associated with dosage compensation status of Z genes. We also find a trend for a higher proportion of CpG islands in the region of the Z chromosome with the fewest dosage-compensated genes compared with the region containing the greatest concentration of compensated genes. Comparison between chicken and platypus genomes shows that LINE elements are not enriched on sex chromosomes in platypus, indicating that LINE accumulation is not a feature of all sex chromosomes. Our results suggest that CpG islands are not randomly distributed on the Z chromosome and may influence Z gene dosage compensation status

The Status of Dosage Compensation in the Multiple X Chromosomes of the Platypus

Dosage compensation has been thought to be a ubiquitous property of sex chromosomes that are represented differently in males and females. The expression of most X-borne genes is equalized between XX females and XY males in therian mammals (marsupials and “placentals”) by inactivating one X chromosome in female somatic cells. However, compensation seems not to be strictly required to equalize the expression of most Z-borne genes between ZZ male and ZW female birds. Whether dosage compensation operates in the third mammal lineage, the egg-laying monotremes, is of considerable interest, since the platypus has a complex sex chromosome system in which five X and five Y chromosomes share considerable genetic homology with the chicken ZW sex chromosome pair, but not with therian XY chromosomes. The assignment of genes to four platypus X chromosomes allowed us to examine X dosage compensation in this unique species. Quantitative PCR showed a range of compensation, but SNP analysis of several X-borne genes showed that both alleles are transcribed in a heterozygous female. Transcription of 14 BACs representing 19 X-borne genes was examined by RNA-FISH in female and male fibroblasts. An autosomal control gene was expressed from both alleles in nearly all nuclei, and four pseudoautosomal BACs were usually expressed from both alleles in male as well as female nuclei, showing that their Y loci are active. However, nine X-specific BACs were usually transcribed from only one allele. This suggests that while some genes on the platypus X are not dosage compensated, other genes do show some form of compensation via stochastic transcriptional inhibition, perhaps representing an ancestral system that evolved to be more tightly controlled in placental mammals such as human and mouse

Cesare Bisoni, Elisabetta Gualandri, Andrea Landi e Giuseppe Lusignani (a cura di) Lo stato della finanza. Scritti in onore di Marco Onado

Raccolta di saggi di allievi e colleghi in onore del Prof. Marco Onad

Compact, multi-channel, electronic interface for PNS recording and stimulation

A multi-channel system for neural signal recording/stimulation is presented. The system is split on two devices: an implantable High Voltage (HV) CMOS integrated circuit (IC) hosting a sigma delta modulator, together with a low noise preamplifier/prefilter and a digital platform for sigma delta decimation/control implemented on a FPGA. This innovative approach guarantees a robust communication link while minimizing the blocks to be implanted, saving power and area. The recording unit exhibits an IRN = 2.12uVrms in 800Hz-8kHz bandwidth, a programmable gain in the range 45.4dB-58dB and a 14-bit A/D conversion. The IC hosts also a current-mode stimulator able to deliver currents in the range of hundreds of microampere to electrodes with impedances up to 100kΩ

An HV-CMOS integrated circuit for neural stimulation in prosthetic applications

An integrated neural stimulator for prosthetic applications, realized with a high-voltage CMOS 0.35-µm process, is presented. The device is able to provide biphasic current pulses to stimulate eight electrodes independently. A voltage booster generates a 17-V voltage supply in order to guarantee the programmed stimulation current even in case of high impedances at the electrode–tissue interface. Pulse parameters such as amplitude, frequency, and width can be programmed digitally. The device has been successfully tested by means of both electrical and in vivo tests, and the results show its capability to provide currents on the order of hundreds of microamperes with impedances on the order of tens of kiloohms

A bidirectional interface to the peripheral neural system based on a sigma delta recording unit and on a high voltage stimulator

Over the last years many scientific advances have been done on the development of neural prostheses [1] for hand amputees. Recent achievements in this field have made this challenge easier with the introduction of innovative biocompatible materials and the production of smart, light, artificial limbs characterized by lots of freedom degrees [2]. Despite such improvements, the communication between an implanted electrode and a prosthetic limb is still an open issue, due to long cables and cumbersome electronic equipments that typically separate them. In this contest it is very important the miniaturization of the electronic used to acquire the neural signals from efferent fibers of the Peripheral Nervous System (PNS) and to elicitate the afferent axons in order to restore the sensory feedback. Due to the weak amplitude of neural signals, this kind of design is particularly critical. Indeed neural signals are drowned in a noisy environment characterized by other biological electrical sources such as Electromyographic (EMG) interferences which have amplitudes many orders of magnitude greater than that of the neural signal and a bandwidth very close to them. The system proposed in this paper is based on a sigma delta converter divided into two main blocks: an on-chip analog front-end, that includes a sigma delta modulator and a digital part, realized off- chip on a FPGA. The main aim is to move the majority of the complexity on the digital side, keeping the analog part as simple as possible. The CMOS recording chip, designed on an AMS 0.35um process, contains 8 parallel readout channels and has a 4.1mm x 4.1mm die size. Several parameters (amplifier gain, opamp bandwidths, etc.) are programmable. Fig. 1 shows the chip test results for an input trace obtained from real measurements of an electrode implanted in a rat sciatic nerve. The original signal is largely affected by low-frequency noise (ECG and EMG) which is completely removed by the system. Regarding the stimulation unit another CMOS analog chip has been designed. It is able to deliver biphasic current pulses whose shape and parameters are summarized in Fig. 2 (on the left). The system is based on a single supply with anodic and cathodic active phases. Fig. 2 (on the right) shows the stimulation diagram. The stimulation is enabled by closing switch S1 whereas with switch S2 it is possible to select between anodic or cathodic phase. Even though the positive and negative currents have the same value, a residual charge can be accumulated at the electrode-nerve interface due to mismatches in the two current paths. As a result, some electrochemical damaging processes can occur at this interface. Therefore, to avoid charge accumulation, a periodic charge cancellation phase is necessary. A switch S3 has been introduced to periodically shortcut the two electrode terminals removing all the stored charge. Due to the high value and to the high variability of the electrode-tissue impedance, a programmable high voltage stimulator is required. The designed stimulation system (Fig. 3) is based on a low voltage 6-bit current DAC used to setup the stimulation current level. The current is then converted from a low into a high voltage signal by the output stage and injected into the nerve. The high voltage supply for the output stage is generated by a programmable voltage booster that increases the voltage up to 20V. The stimulation unit and in particular the voltage booster has been designed achieving a good compromise between size and boosting time. The IC has been designed on an AMS High Voltage 0.35um CMOS process which includes both low voltage and high voltage transistors. Fig. 4 shows the stimulating chip layout

A multi-channel recording/stimulation device for neuro-prosthetic application

In this paper a system for neural recording and stimulation is presented. The device is composed of two different IC: a recording chip, implemented in a 3.3V 0.35µm CMOS technology, and a stimulation chip, realized with a High Voltage 0.35µm CMOS process. The recording module is able to acquire neural signals from the Peripheral Nervous System (PNS), amplifying, filtering and converting them in a digital format. The stimulation chip can provide stimulation currents in the range of hundreds of microamperes with impedances up to tens of kOhm, thanks to a voltage booster that brings the voltage supply up to 19V. The ICs, hosted in a custom PCB, communicate with the PC thanks to a Xilinx-Spartan6 LX45 prototyping board. The experimental measures show the system capabilities to record signals in the range of few microvolts with a total IRN of 4µVrms and to generate programmable biphasic current pulse trains