Progress in the analysis of single-cell transcriptome and developmental trajectories of early mouse embryonic inner ear ganglion cells

On March 22, Cell Reports published online a research paper titled Single-cell transcriptomic landscapes of the otic neuronal lineage at multiple early embryonic ages.
, State Key Laboratory of Neuroscience, Liu Zhiyong's research group of Shanghai Brain Science and Brain-like Research Center and Wei Wu's research group of Shanghai Institute of Nutrition and Health, Chinese Academy of Sciences
.

This study revealed the single-cell transcriptome characteristics of mouse inner ear ganglion lineage at three different embryonic stages E9.
5, E11.
5, and E13.
5, and newly discovered a variety of otic capsule neural precursor cells and ganglionic subtypes.
type-specific genes
.

The results of this study provide a new theoretical basis for the treatment of balance and auditory dysfunction caused by abnormal inner ear ganglia
.

The vestibular ganglion (VGN) and the spiral ganglion (SGN) of the inner ear play key roles in maintaining body balance and perceiving sound information, respectively, and their damage or degeneration can lead to balance disorders and deafness
.

Among them, the spiral ganglion is crucial to the clinical efficacy of cochlear implants
.

Although mature inner ear vestibular ganglia and spiral ganglia have different functions, they both originate from early embryonic otic capsule neuroblasts, also known as cochlear vestibular ganglion precursor cells (CVGs)
.

At present, there are three important questions to be answered in the field: 1.
How are the cochlear vestibular ganglion precursor cells generated from the ear capsule? 2.
How do undifferentiated cochlear vestibular ganglion precursor cells gradually differentiate into inner ear vestibular ganglia and spiral ganglia? 3.
How many cell subtypes are there in the vestibular and spiral ganglia of the inner ear in the early embryo? The systematic study of these questions will not only help to reveal the molecular mechanisms of inner ear ganglion development in mice, but also apply these key genes or gene networks during development to regenerate and repair adult inner ear vestibular ganglia and spiral ganglia
.

Using 10x Genomics single-cell transcriptome sequencing technology, this study revealed the transcriptomic signature of the mouse inner ear in the early embryonic stage (Figure 1A)
.

It was found that cells in the anterior ventral side of the ear capsule began to migrate out of the ear capsule and gradually lost epithelial characteristics as neurogenesis of the ear capsule progressed (Fig.
1B)
.

At E9.
5 stage, some Neurog1+ otic capsule cells begin to express Insm1 and Shox2, and finally form cochlear vestibular ganglion precursor cells
.

Between E9.
5 and E11.
5, the generation of new cochlear vestibular ganglion precursor cells and the differentiation of old cochlear vestibular ganglion precursor cells proceeded simultaneously (Fig.
1D, Fig.
2)
.

The vestibular and spiral ganglia of the inner ear already exhibited significantly different gene expression profiles at E11.
5
.

In addition to verifying the specific genes of cochlear vestibular ganglion precursor cells, inner ear vestibular ganglia and spiral ganglia at different stages in vivo using in situ hybridization and lineage tracing experiments, this study also constructed 2 new transgenic mouse models Shox2 -P2A-Cre/+ and Casz1*3xHA-P2A-Tdtomato/+ can be used for subsequent more accurate inner ear ganglion labeling and gene function analysis
.

The researchers aggregated three different stages of undifferentiated cochlear vestibular ganglion precursor cells and differentiated inner ear vestibular ganglia and spiral ganglia for developmental trajectory fitting analysis
.

The findings suggest that the spiral ganglion subtype has not yet emerged at the E13.
5 stage
.

In contrast, the inner ear vestibular ganglion lineage already exists in two subtypes at E13.
5 (Fig.
2): Tlx3+/Sall3+/Gata3- type I inner ear vestibular ganglion and Tlx3+/Sall3-/Gata3+ type II inner ear vestibular ganglion ganglia
.

Therefore, the vestibular ganglion subtype of the inner ear appeared earlier than the spiral ganglion subtype
.

The specific neural functions of these cell subtypes will be an important future research direction
.

The research was supported by the Ministry of Science and Technology, the Chinese Academy of Sciences, the National Natural Science Foundation of China, and Shanghai
.

Figure 1 Transcriptome analysis of the ear capsule in the early mouse embryo
.

(A) Schematic diagram of 10xGenomics single-cell sequencing experiments in embryonic E9.
5, E11.
5 and E13.
5 ear capsules; (B) E9.
5 ear capsule cells can be divided into epithelial cell populations (grey) and cochlear vestibular precursor neurons (CVG, pink); (C) E11.
5 otic capsule neural lineage cells divided into three groups, differentiated vestibular ganglion (VGN, blue) and spiral ganglion (SGN, green) and undifferentiated CVG cells (pink); (D) E13.
5 inner ear neurons divided into undifferentiated CVG cells (pink), SGN (green), and type I VGN (purple) and type II VGN (yellow) Figure 2 Cochlear vestibular precursor nerve Schematic diagram of early embryonic development of segmental (CVG) cells Source: Center for Excellence in Brain Science and Intelligent Technology, Chinese Academy of Sciences