Advances in molecular profiling have opened up the possibility to map the expression of genes in cells, tissues, and organs in the human body. Here, we combined single-cell transcriptomics analysis with spatial antibody-based protein profiling to create a high-resolution single–cell type map of human tissues. An open access atlas has been launched to allow researchers to explore the expression of human protein-coding genes in 192 individual cell type clusters. An expression specificity classification was performed to determine the number of genes elevated in each cell type, allowing comparisons with bulk transcriptomics data. The analysis highlights distinct expression clusters corresponding to cell types sharing similar functions, both within the same organs and between organs.

The novel SARS-coronavirus 2 (SARS-CoV-2) poses a global challenge on healthcare and society. For understanding the susceptibility for SARS-CoV-2 infection, the cell type-specific expression of the host cell surface receptor is necessary. The key protein suggested to be involved in host cell entry is angiotensin I converting enzyme 2 (ACE2). Here, we report the expression pattern of ACE2 across > 150 different cell types corresponding to all major human tissues and organs based on stringent immunohistochemical analysis. The results were compared with several datasets both on the mRNA and protein level. ACE2 expression was mainly observed in enterocytes, renal tubules, gallbladder, cardiomyocytes, male reproductive cells, placental trophoblasts, ductal cells, eye, and vasculature. In the respiratory system, the expression was limited, with no or only low expression in a subset of cells in a few individuals, observed by one antibody only. Our data constitute an important resource for further studies on SARS-CoV-2 host cell entry, in order to understand the biology of the disease and to aid in the development of effective treatments to the viral infection.

The international spread of the novel, pathogenic SARS-coronavirus 2 (SARS-CoV-2) poses a global challenge on both healthcare and society. A multitude of research efforts worldwide aim at characterizing the cellular factors involved in viral transmission in order to reveal therapeutic targets. For a full understanding of the susceptibility for SARS-CoV-2 infection, the cell type-specific expression of the host cell surface receptor is necessary. The key protein suggested to be involved in host cell entry is Angiotensin I converting enzyme 2 (ACE2), and its expression has been reported in various human organs, in some cases with inconsistent or contradictory results. Here, we aim to verify a reliable expression profile of ACE2 in all major human tissues and cell types. Based on stringently validated immunohistochemical analysis and highthroughput mRNA sequencing from several datasets, we found that ACE2 expression is mainly localized to microvilli of the intestinal tract and renal proximal tubules, gallbladder epithelium, testicular Sertoli cells and Leydig cells, glandular cells of seminal vesicle and cardiomyocytes. The expression in several other previously reported locations, including alveolar type II (AT2) cells, could not be confirmed. Furthermore, ACE2 expression was absent in the AT2 lung carcinoma cell line A549, often used as a model for viral replication studies. Our analysis suggests that the expression of ACE2 in the human respiratory system appears to be limited, and the expression of the receptor in lung or respiratory epithelia on the protein level is yet to be confirmed. This raises questions regarding the role of ACE2 for infection of human lungs and highlights the need to further explore the route of transmission during SARS-CoV-2 infection.

The Chromosome-Centric Human Proteome Project aims to identify proteins classed as « missing » in the neXtProt knowledgebase. In this article, we present an in-depth proteomics analysis of the human sperm proteome to identify testis-enriched missing proteins. Using a range of protein extraction procedures and LC-MS/MS analysis, we detected a total of 235 proteins (PE2-PE4) for which no previous evidence of protein expression was annotated. Through a combination of LC-MS/MS and LC-PRM analysis, data mining and immunohistochemistry, we were able to confirm the expression of 206 missing proteins (PE2-4) in line with current HPP guidelines (version 2.0). Parallel Reaction Monitoring (PRM) acquisition combined with synthetic heavy labeled peptides was used to target 36 « one-hit wonder » candidates selected on the basis of prior PSM assessment. Of this subset of candidates, 24 were validated with additional predicted and specifically targeted peptides. Evidence was found for a further 16 missing proteins using immunohistochemistry on human testis sections. The expression pattern for some of these proteins was specific to the testis, and they could potentially be valuable markers with applications in fertility assessment. Strong evidence was also found for the existence of 4 proteins labeled as "uncertain" (PE5); the status of these proteins should therefore be re-examined.Our results show how the use of a range of sample preparation techniques combined with MS-based analysis, expert knowledge and complementary antibody-based techniques can produce data of interest to the community.