Bumble bees are characterized by their thick setal pile that imparts aposematic color patterns often used for species-level identification. Like all bees, the single-celled setae of bumble bees are branched, an innovation thought important for pollen collection. To date no studies have quantified the types of setal morphologies and their distribution on these bees, information that can facilitate understanding of their adaptive ecological function. This study defines several major setal morphotypes in the common eastern bumble bee Bombus impatiens Cresson, revealing these setal types differ by location across the body. The positions of these types of setae are similar across individuals, castes, and sexes within species. We analyzed the distribution of the two most common setal types (plumose and spinulate) across the body dorsum of half of the described bumble bee species. This revealed consistently high density of plumose (long-branched) setae across bumble bees on the head and mesosoma, but considerable variation in the amount of metasomal plumosity. Variation on the metasoma shows strong phylogenetic signal at subgeneric and smaller group levels, making it a useful trait for species delimitation research, and plumosity has increased from early Bombus ancestors. The distribution of these setal types suggests these setae may serve several functions, including pollen-collecting and thermoregulatory roles, and probable mechanosensory functions. This study further examines how and when setae of the pile develop, evidence for mechanosensory function, and the timing of pigmentation as a foundation for future genetic and developmental research in these bees.

Tumorigenesis is a multi-step process shaped by the accumulation of somatic driver mutations, but identifying the earliest steps and cell of origin of tumorigenesis remains challenging. Single cell genomics in >1.7 million single cells across donors with the cancer predisposition syndrome neurofibromatosis type 1 (NF-1), shows that somatic ‘second-hit’ mutations in NF1 are pervasive and show positive clonal selection in oligodendrocytes (OLs) and OL precursor cells (OPCs), but are exceedingly rare in neurons and other lineages. Combined spatial genotyping and transcriptomic analysis enabled dissection of cell autonomous and non-autonomous effects of second-hit mutations including clonal expansion of mutant OPCs with strong bias for cerebral gray matter versus white matter, suggesting that gray matter influences OPC proliferation and differentiation via non-cell autonomous interactions between OPCs and neurons. NF1 -null OL lineage cells upregulate CDKN2A —a tumor suppressor frequently lost in NF1 -mutant tumors— whereas brain cancers from these same individuals show CDKN2A loss across multiple cancer cell states, suggesting CDKN2A loss in OPCs is a critical step in tumor progression. Our findings reveal developmentally early, exquisitely lineage-specific NF1 somatic mutations in premalignant NF-1 brain, suggest cell autonomous and non-autonomous roles in clonal selection in brain, and suggest that clones harboring cancer driver mutations can persist over a lifetime in phenotypically normal tissues.

Cerebral cavernous malformations (CCM) are a neurovascular anomaly that may occur sporadically in otherwise healthy individuals, or be inherited by autosomal dominant mutations in the genes that encode the proteins of the CCM signaling complex ( KRIT1, CCM2 , or PDCD10 ) ^1–4 . CCMs have long been known to follow a genetic two-hit model where lesion formation is initiated by somatic mutations resulting in biallelic loss of a CCM complex gene ^5–8 . Recent studies have shown that somatic mutations in MAP3K3 and PIK3CA also contribute to CCM pathogenesis ^9–11 ; however, it remains unclear how these mutations contribute to sporadic versus familial cases. Here we show that somatic mutations in MAP3K3 are mutually exclusive with mutations in CCM complex genes and that mutations in MAP3K3 contribute to sporadic, but not familial CCM. Using single-nucleus DNA sequencing, we show that co-occurring MAP3K3 and PIK3CA mutations are present within the same clonal population of cells. Furthermore, we identify PIK3CA mutations in CCM-associated developmental venous anomalies (DVA). It has long been known that sporadic CCM often develop in the vicinity of a DVA. However, the underlying cause of this association is unknown ^12–14 . In this first report of the molecular pathology of CCM-associated DVA, we find that the identical PIKC3A mutation is found in both the DVA and its associated CCM, but that an activating MAP3K3 mutation appears only in the CCM. These results support a mechanism where DVA develop as the result of a PIK3CA mutation, creating a region of the brain vasculature that functions as a genetic primer for CCM development following acquisition of an additional somatic mutation.