Similar multicellular structures can evolve within the same organism that may have different evolutionary histories, be controlled by different regulatory pathways, and play similar but nonidentical roles. In the human fungal pathogen Candida albicans, a quite extraordinary example of this has occurred. Depending upon the configuration of the mating type locus (a/α versus a/a or α/α), C. albicans forms alternative biofilms that appear similar morphologically, but exhibit dramatically different characteristics and are regulated by distinctly different signal transduction pathways. Biofilms formed by a/α cells are impermeable to molecules in the size range of 300 Da to 140 kDa, are poorly penetrated by human polymorphonuclear leukocytes (PMNs), and are resistant to antifungals. In contrast, a/a or α/α biofilms are permeable to molecules in this size range, are readily penetrated by PMNs, and are susceptible to antifungals. By mutational analyses, a/α biofilms are demonstrated to be regulated by the Ras1/cAMP pathway that includes Ras1→Cdc35→cAMP(Pde2—|)→Tpk2(Tpk1)→Efg1→Tec1→Bcr1, and a/a biofilms by the MAP kinase pathway that includes Mfα→Ste2→ (Ste4, Ste18, Cag1)→Ste11→Hst7→Cek2(Cek1)→Tec1. These observations suggest the hypothesis that while the upstream portion of the newly evolved pathway regulating a/a and α/α cell biofilms was derived intact from the upstream portion of the conserved pheromone-regulated pathway for mating, the downstream portion was derived through modification of the downstream portion of the conserved pathway for a/α biofilm formation. C. albicans therefore forms two alternative biofilms depending upon mating configuration.

Prostate cancer is the second most common malignancy in men worldwide and consists of a mixture of tumor and non-tumor cell types. To characterize the prostate cancer tumor microenvironment, we perform single-cell RNA-sequencing on prostate biopsies, prostatectomy specimens, and patient-derived organoids from localized prostate cancer patients. We uncover heterogeneous cellular states in prostate epithelial cells marked by high androgen signaling states that are enriched in prostate cancer and identify a population of tumor-associated club cells that may be associated with prostate carcinogenesis. ERG-negative tumor cells, compared to ERG-positive cells, demonstrate shared heterogeneity with surrounding luminal epithelial cells and appear to give rise to common tumor microenvironment responses. Finally, we show that prostate epithelial organoids harbor tumor-associated epithelial cell states and are enriched with distinct cell types and states from their parent tissues. Our results provide diagnostically relevant insights and advance our understanding of the cellular states associated with prostate carcinogenesis.

Germ cells develop as a cyst of interconnected sibling cells in a broad range of organisms in both sexes. A well-established function of intercellular connectivity is to transport cytoplasmic materials from ‘nurse’ cells to oocytes, a critical process for developing functional oocytes in ovaries of many species. However, there are situations where connectivity exists without a nursing mechanism, and the biological meaning of such connectivity remains obscure. In this review, we summarize the current knowledge on the formation of intercellular connectivity, and discuss its meaning by visiting multiple examples of germ cell connectivity observed in evolutionarily distant species.

rDNA loci, composed of hundreds of tandemly duplicated arrays of rRNA genes, are known to be among the most unstable genetic elements due to their repetitive nature. rDNA instability underlies aging (replicative senescence) in yeast cells, however, its contribution to the aging of multicellular organisms is poorly understood. In this study, we investigate the dynamics of rDNA loci during aging in the Drosophila male germline stem cell (GSC) lineage, and show that rDNA copy number decreases during aging. Our study further reveals that this age-dependent decrease in rDNA copy number is heritable from generation to generation, yet GSCs in young animals that inherited reduced rDNA copy number are capable of recovering normal rDNA copy number. Based on these findings, we propose that rDNA loci are dynamic genetic elements, where rDNA copy number changes dynamically yet is maintained through a recovery mechanism in the germline.

Like MTL-heterozygous (a/␣) cells, white MTL-homozygous (a/a or ␣/␣) cells of Candida albicans, to which a minority of opaque cells of opposite mating type have been added, form thick, robust biofilms. The latter biofilms are uniquely stimulated by the pheromone released by opaque cells and are regulated by the mitogenactivated protein kinase signal transduction pathway. However, white MTL-homozygous cells, to which opaque cells of opposite mating type have not been added, form thinner biofilms. Mutant analyses reveal that these latter biofilms are self-induced. Self-induction of a/a biofilms requires expression of the ␣-receptor gene STE2 and the ␣-pheromone gene MF␣, and self-induction of ␣/␣ biofilms requires expression of the a-receptor gene STE3 and the a-pheromone gene MFa. In both cases, deletion of WOR1, the master switch gene, blocks cells in the white phenotype and biofilm formation, indicating that self-induction depends upon low frequency switching from the white to opaque phenotype. These results suggest a self-induction scenario in which minority opaque a/a cells formed by switching secrete, in a mating-type-nonspecific fashion, ␣-pheromone, which stimulates biofilm formation through activation of the ␣-pheromone receptor of majority white a/a cells. A similar scenario is suggested for a white ␣/␣ cell population, in which minority opaque ␣/␣ cells secrete a-pheromone. This represents a paracrine system in which one cell type (opaque) signals a second highly related cell type (white) to undergo a complex response, in this case the formation of a unisexual white cell biofilm.Approximately 90% of Candida albicans isolates are a/␣ and 10% either a/a or ␣/␣ (24, 25, 50). For a/␣ strains to mate, they must undergo homozygosis to a/a or ␣/␣ (20, 21, 29). Then, a/a and ␣/␣ strains must switch from the white to opaque phenotype (46) in order to be mating competent (27,30). Opaque cells secrete a cell type-specific pheromone, which stimulates the mating response in cells of opposite mating type (5,26,38). However, in a fashion unique to C. albicans, these pheromones also induce mating-incompetent white cells, but not matingcompetent opaque cells, of opposite mating type to form robust biofilms, similar morphologically to those formed by a/␣ cells (13, 42-44, 48, 53-55). These MTL-homozygous white cell biofilms have been demonstrated in vitro to facilitate mating between opaque a/a and ␣/␣ cells (13,48).Although the addition of minority opaque cells of opposite mating type (1 to 10%) to a population of white cells increases the thickness of the final white cell biofilm by more than 50%, single-sex white a/a or ␣/␣ cell populations, to which cells of opposite mating types have not been added, also form robust biofilms composed of a basal layer of yeast cells and a thick upper layer of hyphae and matrix (13,(42)(43)(44)(53)(54)(55). We previously showed that deletion of the ␣-receptor gene STE2 results in highly reduced, abnormal white a/a cell biofilms in the absence of minority opaque ␣/␣ cells, suggesting t...