CFAP100 couples microtubule glutamylation to spindle pole integrity in keratinocytes to promote epidermal development

Introduction

The epidermis is a stratified squamous epithelium essential for the skin-barrier function¹. Abnormalities in the epidermis are associated with numerous skin diseases, including atopic dermatitis, psoriasis, and xerosis. Epidermal development begins with a monolayer of epithelial cells derived from the ectoderm, termed basal keratinocytes^2,3. In mice, from embryonic day 9.5 (E9.5) to E12.5, basal keratinocytes divide parallel to the basement membrane, rapidly increasing their number to accommodate embryonic growth in the surface area. From E15.5 to E17.5, most basal keratinocytes begin to divide vertically, leading to an increase in the cell number and a sequential formation of the spinous layer, granular layer, and stratum corneum, ultimately assembling into a mature epidermis^{3, 4–5}. Therefore, proper keratinocyte division is crucial for the expansion of the epidermal area and the establishment of its stratified layers. Dysregulation of keratinocyte division can impair the transition of keratinocytes from the basal layer to the suprabasal layers^4,6. However, the precise mechanisms that govern the division of keratinocytes are still elusive.

There is accumulating evidence that the microtubule cytoskeleton assembled from α/β-tubulin heterodimers plays a critical role in keratinocyte division to support epidermal development^{7, 8–9}. Especially, microtubules are essential for orienting the mitotic spindle to establish the axis of keratinocyte division, in addition to their classic role in orchestrating chromosome segregation^10,11. The organization, dynamics, and functions of microtubules in cell division are exquisitely regulated by microtubule-binding proteins^8,10. For instance, microtubule plus end-tracking proteins, such as end-binding protein 1 and cytoplasmic linker protein 170, play a significant role in mediating the microtubule-kinetochore attachment^{12, 13, 14–15}. Spindle pole-associated proteins, such as targeting protein for Xklp2, are involved in spindle pole assembly and microtubule flux towards spindle poles^{16, 17–18}. How microtubule-binding proteins function to regulate the spindle behavior during keratinocyte division is poorly understood.

In addition to microtubule-binding proteins, post-translational modifications, such as acetylation and glutamylation, are known to control microtubule properties and functions^19,20. Microtubule glutamylation is catalyzed by enzymes of the tubulin tyrosine ligase-like protein (TTLL) family. Conversely, enzymes of the cytosolic carboxypeptidase (CCP) family remove glutamyl groups from microtubules^{21, 22, 23–24}. The distribution of glutamylated microtubules exhibits spatiotemporal dynamics. In quiescent...