Selective targeting of striatal parvalbumin-expressing interneurons for transgene delivery

Application of a split-Cre system for high-capacity adenoviral vector amplification

BACKGROUND AND AIMS

High-capacity adenoviral vectors (HC-AdV) show extended DNA payload and stability of gene expression in vivo due to the absence of viral coding sequences. However, production requires methods to trans-complement viral proteins, usually through Helper Viruses (HV). The Cre/loxP system is frequently employed to remove the packaging signal in HV genomes, in order to avoid their encapsidation. However, chronic exposure to the Cre recombinase in packaging cells is detrimental. We have applied the dimerizable Cre system to overcome this limitation.

METHODS AND RESULTS

Cre was split in two fragments devoid of recombinase function (N-terminal 244 and C-terminal 99 amino-acids). In one version of the system, interaction with both moieties was favored by rapamycin-dependent heterodimerization domains (DiCre). Other version contained only Cre sequences (oCre). We generated packaging cells and HVs expressing the complementary fragments and studied their performance for HC-AdV production. We found that both conformations avoided interference with the growth of packaging cells, and the oCre system was particularly suitable for HC-AdV amplification.

CONCLUSIONS

The split-Cre system improves the performance of packaging cells and can reduce the time and cost of HC-AdV amplification up to 30% and 15%, respectively. This may contribute to the standardization of HC-AdV production.

AAV13 Enables Precise Targeting of Local Neural Populations

As powerful tools for local gene delivery, adeno-associated viruses (AAVs) are widely used for neural circuit studies and therapeutical purposes. However, most of them have the characteristics of large diffusion range and retrograde labeling, which may result in off-target transduction during in vivo application. Here, in order to achieve precise gene delivery, we screened AAV serotypes that have not been commonly used as gene vectors and found that AAV13 can precisely transduce local neurons in the brain, with a smaller diffusion range than AAV2 and rigorous anterograde labeling. Then, AAV13-based single-viral and dual-viral strategies for sparse labeling of local neurons in the brains of C57BL/6 or Cre transgenic mice were developed. Additionally, through the neurobehavioral test in the ventral tegmental area, we demonstrated that AAV13 was validated for functional monitoring by means of carrying Cre recombinase to drive the expression of Cre-dependent calcium-sensitive indicator. In summary, our study provides AAV13-based toolkits for precise local gene delivery, which can be used for in situ small nuclei targeting, sparse labeling and functional monitoring.

Neuron types in the primate striatum: stereological analysis of projection neurons and interneurons in control and parkinsonian monkeys

AIMS

The striatum is mainly composed of projection neurons. It also contains interneurons, which modulate and control striatal output. The aim of the present study was to assess the percentages of projection neurons and interneuron populations in the striatum of control monkeys and of parkinsonian monkeys.

METHODS

Unbiased stereology was used to estimate the volume density of every neuron population in the caudate, putamen and ventral striatum of control monkeys and of monkeys treated with MPTP, which results in striatal dopamine depletion. The various neuron population phenotypes were identified by immunohistochemistry. All analyses were performed within the same subjects using similar processing and analysis parameters, thus allowing for reliable data comparisons.

RESULTS

In control monkeys, the projection neurons, which express the Dopamine-and-cAMP-Regulated-Phosphoprotein, 32-KDa (DARPP-32), were the most abundant: ~86% of the total neurons counted. The interneurons accounted for the remaining 14%. Among the interneurons, those expressing Calretinin were the most abundant (Cr+: ~57%; ~8% of the total striatal neurons counted), followed those expressing Parvalbumin (Pv+: ~18 %; 2.6%), Dinucleotide Phosphate-Diaphorase (NADPH+: ~13 %; 1.8%), Choline Acetyltransferase (ChAT+: ~11%; 1.5%) and Tyrosine Hydroxylase (TH+: ~0.5%; 0.1%). No significant changes in volume densities occurred in any population following dopamine depletion, except for the TH+ interneurons, which increased in parkinsonian non-symptomatic monkeys and even more in symptomatic monkeys.

CONCLUSIONS

These data are relevant for translational studies targeting specific neuron populations of the striatum. The fact that dopaminergic denervation does not cause neuron loss in any population has potential pathophysiological implications.