Insights into the Spatial and Temporal Dynamics of Motile Cilia Regeneration in Xenopus Multiciliated Epithelium

Core Concepts

Xenopus multiciliated cells can regenerate cilia without the transition zone, which assembles later, and require new protein synthesis to complete cilia regeneration.

Abstract

The study investigates the mechanisms of cilia regeneration in the multiciliated epithelium of Xenopus embryos. Key findings:

Deciliation in Xenopus multiciliated cells (MCCs) removes the transition zone (TZ) along with the ciliary axoneme, unlike unicellular organisms.

MCCs can initiate ciliary axoneme assembly without the TZ, and the TZ assembles later during regeneration. Ciliary tip proteins like Sentan and Clamp localize to the regenerating cilia immediately.

The TZ protein B9d1 requires new transcription and translation for its assembly, leading to the delayed TZ regeneration.

When protein synthesis is blocked, MCCs preferentially assemble fewer but longer cilia by redistributing the limited pool of ciliary proteins among a subset of basal bodies. Mathematical modeling suggests that cilia length is a major determinant of force generation by MCCs.

The study provides insights into the spatial-temporal sequence of cilia assembly and the role of the TZ, as well as how cells optimize organelle size and number to maximize function.

Stats

Cilia length pre-deciliation: 14.87 ± 2.38 μm
Cilia length at 1 hour post-deciliation: 2.75 ± 1.04 μm
Cilia length at 3 hours post-deciliation: 8.53 ± 1.74 μm
Cilia length at 6 hours post-deciliation: 14.87 ± 2.38 μm
Number of cilia per MCC in vehicle treatment at 1 hour: 41.61 ± 12.71
Number of cilia per MCC in CHX treatment at 1 hour: 33.78 ± 17.27
Number of cilia per MCC in CHX treatment at 3 hours: 14 ± 6
Number of cilia per MCC in CHX treatment at 6 hours: 8 ± 4

Quotes

"Xenopus multiciliated epithelium regenerates cilia in the same MCCs and does not undergo stem cell-based renewal of damaged MCCs."
"Deciliation in Xenopus MCCs removes the TZ with the ciliary axoneme."
"Cells appeared to initiate ciliary axoneme assembly in the absence of B9D1."
"Without protein synthesis during cilia regeneration, MCCs produce few longer-length cilia over multiple short-length cilia."

Key Insights Distilled From

Mechanisms of cilia regeneration in Xenopus multiciliated epithelium in vivo

by Rao,V. G., S... at www.biorxiv.org 06-14-2023

https://www.biorxiv.org/content/10.1101/2023.06.14.544972v2

Deeper Inquiries

How do the spatial and temporal dynamics of cilia assembly differ between unicellular organisms and vertebrate multiciliated cells?

In unicellular organisms like Chlamydomonas, cilia assembly typically occurs in a bottom-up manner, starting from the basal body and progressing to the ciliary tip. The spatial and temporal dynamics involve the sequential recruitment of proteins at the base of the cilia by Intraflagellar transport proteins (IFTs) to facilitate axoneme growth. In contrast, vertebrate multiciliated cells (MCCs), such as Xenopus MCCs, exhibit unique characteristics in cilia assembly dynamics.
Deciliation in Xenopus MCCs removes the transition zone (TZ) along with the ciliary axoneme, unlike in unicellular organisms where the cilia are typically severed distal to the TZ. This difference suggests a distinct mechanism of cilia severing and regeneration in vertebrate MCCs. Additionally, in Xenopus MCCs, the assembly of the ciliary axoneme can initiate before the reassembly of the TZ, challenging the conventional notion that the TZ precedes axoneme assembly. The ciliary tip proteins, Sentan and Clamp, are immediately trafficked to regenerating cilia without delay, indicating a unique temporal sequence of protein localization during cilia regeneration in vertebrate MCCs.
Overall, the spatial and temporal dynamics of cilia assembly in vertebrate multiciliated cells differ from those in unicellular organisms, highlighting the complexity and diversity of ciliogenesis processes across different biological systems.

What are the potential implications of TZ being dispensable for the initiation of cilia assembly in Xenopus MCCs?

The finding that the transition zone (TZ) is dispensable for the initiation of cilia assembly in Xenopus multiciliated cells (MCCs) has several potential implications for our understanding of ciliogenesis and cellular biology:

Reevaluation of Ciliogenesis Models: The dispensability of the TZ challenges the traditional model of ciliogenesis, which posits that the TZ is essential for ciliary assembly. This discovery prompts a reevaluation of the role of the TZ in ciliogenesis and suggests that cells may have alternative mechanisms for regulating ciliary protein traffic and function.

Dynamic Nature of TZ Proteins: The delayed regeneration of the TZ in Xenopus MCCs suggests a dynamic nature of TZ proteins, where they may be incorporated into the cilia after the axoneme assembly. This dynamic assembly of TZ proteins raises questions about the regulation and function of these proteins during ciliogenesis.

Cellular Decision-Making Processes: The ability of MCCs to initiate cilia assembly without a fully formed TZ implies complex cellular decision-making processes. Cells may prioritize certain aspects of ciliogenesis, such as ciliary axoneme growth, over others, indicating a sophisticated regulatory mechanism for organelle assembly.

Functional Implications: Understanding the dispensability of the TZ in cilia assembly may have implications for ciliopathies and other cilia-related disorders. It could provide insights into the mechanisms underlying cilia dysfunction and potential therapeutic targets for treating ciliopathies.

In summary, the dispensability of the TZ in Xenopus MCCs opens up new avenues for research into ciliogenesis, cellular organization, and the functional significance of the TZ in vertebrate multiciliated cells.

How do MCCs sense and coordinate the distribution of limited ciliary proteins among hundreds of basal bodies to optimize cilia number and length?

Multiciliated cells (MCCs) in vertebrates, such as Xenopus MCCs, face the challenge of distributing limited ciliary proteins among hundreds of basal bodies to optimize cilia number and length during regeneration. Several mechanisms may be involved in how MCCs sense and coordinate this distribution:

Protein Redistribution: MCCs may dynamically redistribute ciliary proteins among basal bodies to ensure the assembly of a subset of cilia with optimal length. Proteins essential for ciliogenesis, such as Intraflagellar transport proteins (IFTs), may accumulate at select basal bodies to support the growth of longer cilia.

Selective Protein Enrichment: MCCs may selectively enrich certain basal bodies with essential ciliary proteins to prioritize the assembly of cilia that reach near wild-type length. This selective enrichment mechanism allows MCCs to maximize the functional output of individual cilia.

Cellular Decision-Making: MCCs likely employ cellular decision-making processes to determine which basal bodies receive the necessary proteins for cilia assembly. This decision-making may involve sensing the length of regenerating cilia and prioritizing the allocation of proteins to basal bodies based on ciliary growth status.

Optimization of Force Generation: By optimizing cilia number and length, MCCs can generate optimal beating force necessary for mechanical coupling with surrounding MCCs. The coordination of protein distribution among basal bodies may be geared towards maximizing force generation and maintaining coordinated ciliary beating.

Overall, the sensing and coordination of limited ciliary proteins among hundreds of basal bodies in MCCs involve complex regulatory mechanisms that ensure the efficient assembly of cilia with the appropriate length and functional capacity. This process highlights the remarkable adaptability and precision of cellular mechanisms in orchestrating organelle assembly and function.