A Comprehensive Toolbox for Genetic Targeting of the Claustrum in Mice

Centrala begrepp

The authors have developed a series of genetically engineered mouse lines that enable specific and comprehensive targeting of claustrum neurons, providing new tools to study the functions of this enigmatic brain structure.

Sammanfattning

The claustrum (CLA) is a small, sheet-like subcortical structure in the mammalian brain that has been associated with a variety of functions, from consciousness to impulse control. However, research on the CLA has been challenging due to difficulties in specifically and comprehensively targeting its neuronal populations.

The authors identified the Smim32 gene as being almost exclusively expressed in excitatory neurons of the CLA and endopiriform nucleus, as well as in inhibitory neurons of the thalamic reticular nucleus. Leveraging this unique expression pattern, they developed a series of Cre- and Flippase-expressing knockin and BAC transgenic mouse lines with different expression profiles.

The Smim32-Cre and Smim32-Flpo knockin lines, as well as the Tg(Smim32-Cre)61Irod and Tg(Smim32-Cre)62Irod BAC transgenic lines, allow for specific and comprehensive targeting of CLA neurons. These novel genetic tools provide new standards for the interrogation of CLA function and enable a wide range of applications, including cell-type specific labeling, manipulation, and analysis of CLA neurons.

The authors demonstrate the versatility of these lines by combining them with various Cre-inducible genetic tools, such as viral vectors, designer receptors, and calcium indicators. These tools offer new possibilities for the functional dissection of the CLA and its role in diverse brain functions.

Statistik

The authors report that in the CLA, 94% of all Smim32-positive cells co-expressed the known CLA marker Nr4a2, while about 80% of all Nr4a2-positive cells within the CLA co-expressed Smim32.
In the thalamic reticular nucleus (TRN), 96% of all Smim32-positive cells co-expressed the inhibitory neuron marker Pvalb, and 54% of all Pvalb-positive cells co-expressed Smim32.

Citat

"Smim32 is expressed in a large majority of CLA excitatory neurons, as well as in a significant proportion of TRN inhibitory neurons."
"The major advantage of the Tg(Smim32-Cre)61Irod mouse line is its high specificity to CLA neurons: the transgene is expressed on average in 70% of CLA projection neurons (Nr4a2+ population), while being only sparsely expressed in the EP and other cell populations of the claustro-insular region."

Viktiga insikter från

A toolbox for genetic targeting of the claustrum

by tuberosa,j.,... på www.biorxiv.org 05-14-2024

https://www.biorxiv.org/content/10.1101/2024.05.13.593837v1

Djupare frågor

What other brain regions or cell types, beyond the CLA and TRN, might express Smim32, and how could this impact the specificity of the genetic tools developed in this study

In addition to the CLA and TRN, other brain regions or cell types that might express Smim32 include the endopiriform nucleus (EP) and a subset of cortical layer 6 neurons. The expression of Smim32 in these additional regions could impact the specificity of the genetic tools developed in this study by potentially leading to off-target effects or unintended manipulation of these cell populations. It is crucial to consider the potential overlap in Smim32 expression between the CLA, EP, and cortical layer 6 neurons when interpreting the results obtained with these genetic tools. Further validation and characterization of the expression patterns of Smim32 in these regions are essential to ensure the specificity and accuracy of the genetic targeting strategies.

How could the authors further validate the functional capabilities of the Smim32-based genetic tools, such as by demonstrating their ability to reliably manipulate CLA neuron activity and associated behaviors

To further validate the functional capabilities of the Smim32-based genetic tools, the authors could conduct additional experiments to demonstrate their ability to reliably manipulate CLA neuron activity and associated behaviors. This could involve performing optogenetic or chemogenetic manipulations using the Cre or Flippase-expressing mouse lines in combination with specific reporter genes or effector molecules. By activating or inhibiting Smim32-expressing neurons in the CLA and observing the resulting changes in behavior or neuronal activity, the authors can provide direct evidence of the tools' effectiveness in modulating CLA function. Additionally, conducting behavioral assays or electrophysiological recordings in response to targeted manipulation of Smim32-expressing neurons can further confirm the specificity and functionality of these genetic tools.

Given the multifunctional nature of the CLA, how might these new genetic tools be leveraged to uncover the specific contributions of CLA neurons to different cognitive and behavioral processes

Given the multifunctional nature of the CLA, these new genetic tools can be leveraged to uncover the specific contributions of CLA neurons to different cognitive and behavioral processes. By selectively targeting and manipulating Smim32-expressing neurons in the CLA, researchers can investigate the role of these neurons in various functions attributed to the CLA, such as consciousness, saliency detection, and synchronization of neuronal activity. The genetic tools developed in this study provide a means to dissect the complex circuitry and functional roles of the CLA in a more precise and targeted manner. By combining these tools with advanced imaging techniques, electrophysiology, and behavioral assays, researchers can gain a deeper understanding of how CLA neurons contribute to specific cognitive processes and behaviors, ultimately shedding light on the functional significance of this enigmatic brain structure.