Material Method Thymic stromal cells were isolated from week 2-old Fam83hwt/wt and Fam83h-/- animals (see above). cTECs were identified as CD45- Ter119- EpCAM+ UEA- Ly.51+ cells and single-cell sorted into 384-well plates already containing 0.3 µL of lysis buffer and 3 µL of silicone oil (100 cSt, Sigma-Aldrich), using the Formulatrix Mantis. As a negative control, a subset of wells received no sorted cells. Generation of smart-seq3xpress libraries (scRNA-seq) Smart-seq3xpress libraries were prepared following published protocol involving reverse transcription and 14 cycles of PCR pre-amplification after sample storage at −80°C. Indexed libraries were generated by transferring cDNA into plates with dried primers, followed by Tn5 tagmentation and PCR amplification for 16 cycles. Libraries were purified using SeraMag and SPRIselect beads, quality-checked on a Fragment Analyzer, quantified by Qubit, and sequenced on an Illumina NextSeq 2000 with 2 × 109 bp paired-end and index reads. Analysis of scRNAseq Data Alignment of Raw Data The raw read files were processed with zUMIs (version 2.7.9e), applying published parameters and settings documented in the supplemental file (Smartseq3xpress_SS3x_manuscript_all.yaml). Reads were aligned with STAR (version 2.7.3a) against mouse genome GRCm38, using gencode.vM8 annotation. Several downsampled count matrices were created, and for downstream analyses, a range of 10,000–20,000 reads per cell was used. Data Processing Subsequent steps were carried out in Seurat (version 5.2.1), focusing on 5′-end tagged reads. Reads mapping to spike-ins (ERCC and SIRV) were excluded, and cells were filtered based on quality metrics (e.g., gene count >1200, RNA count >2200, spike-in <12%, mitochondria <6%). SCTransform with glmGamPoi was used for normalization. Dimensionality reduction and clustering were done using the first 30 principal components, UMAP, and a resolution of 0.8. For integration, 50-dimension CCA via the IntegrateLayers function was applied. Seurat objects were converted to h5ad format and uploaded to Scarfweb. Data is available at https://www.nygen.io.

Abstract: Family of Sequence Similarity 83H (FAM83H/ SACK1H) is primarily expressed in epithelial cells, where it is associated with CK1 and keratins to regulate cytoskeletal organization, cell proliferation, and vesicular trafficking. Mutations in FAM83H cause amelogenesis imperfecta (AI), suggesting its critical role in enamel formation. We generated Fam83h-deficient mice (Fam83hem2(IMPC)Ccpcz, Fam83h-/-) and mice lacking a part of N-terminal CK1-binding domain (Fam83h∆87/∆87). Consistent with other Fam83h-deficient models, these mice are subviable, smaller in size, and display a sparse, scruffy coat, scaly skin, weakness, and hypoactivity. Importantly, both strains exhibit impaired lymphoid cell production during early postnatal development. In the thymus, Fam83h expression is restricted to thymic epithelial cells (TECs), and its deficiency in stromal cells results in disrupted thymic architecture and severe impairment of DN3 (double-negative) T cell expansion, ultimately leading to insufficient T cell production. Single-cell transcriptomic analysis has shown that Fam83h-/- cTECs express lower levels of TEC master regulator Foxn1, along with its multiple target genes. This suggests a role for FAM83H and CK1 in cTEC maturation.