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1. Mycoplasma agassizii, an opportunistic pathogen of tortoises, shows very little genetic variation across the Mojave and Sonoran Deserts

   https://doi.org/10.1371/journal.pone.0245895  

   Luzuriaga-Neira, Agusto; Sandmeier, Franziska C.; Weitzman, Chava L.; Tracy, C. Richard; Bauschlicher, Shalyn N.; Tillett, Richard L.; Alvarez-Ponce, David (February 2021, PLOS ONE)

   Kuo, Chih-Horng (Ed.)

   Mycoplasma agassizii is a common cause of upper respiratory tract disease in Mojave desert tortoises ( Gopherus agassizii ). So far, only two strains of this bacterium have been sequenced, and very little is known about its patterns of genetic diversity. Understanding genetic variability of this pathogen is essential to implement conservation programs for their threatened, long-lived hosts. We used next generation sequencing to explore the genomic diversity of 86 cultured samples of M . agassizii collected from mostly healthy Mojave and Sonoran desert tortoises in 2011 and 2012. All samples with enough sequencing coverage exhibited a higher similarity to M . agassizii strain PS6 T (collected in Las Vegas Valley, Nevada) than to strain 723 (collected in Sanibel Island, Florida). All eight genomes with a sequencing coverage over 2x were subjected to multiple analyses to detect single-nucleotide polymorphisms (SNPs). Strikingly, even though we detected 1373 SNPs between strains PS6 T and 723, we did not detect any SNP between PS6 T and our eight samples. Our whole genome analyses reveal that M . agassizii strain PS6 T may be present across a wide geographic extent in healthy Mojave and Sonoran desert tortoises. 

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2. CT study of the cranial osteology of the short-tailed opossum Monodelphis domestica (Wagner, 1841) (Marsupialia, Didelphidae) and comments on the internal nasal floor skeleton.

   Wible, John R. (December 2022, Annals of Carnegie Museum)

   The individual bones of the adult cranium of the gray short-tailed opossum, Monodelphis domestica (Wagner, 1842) are described and illustrated in multiple views based on CT scans. The author previously reported on the outer bony surfaces of the skull of Monodelphis Burnett, 1830, and the current contribution is a companion piece, paying particular attention to the inner bony surfaces (within the endocranium and nasal cavity) and the facets between individual cranial elements, including the ethmo- and frontoturbinals. Comments are provided on the internal nasal floor skeleton, which in M. domestica includes a fused conglomerate formed by the medial palatine processes of the premaxillae, the vomer, the ethmoid, the presphenoid, and the orbitosphenoids. This conglomerate includes horizontal shelves just dorsal to the hard palate, and occurs widely in marsupials but is currently unknown in monotremes and placentals. 

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3. The genetic basis of differential autodiploidization in evolving yeast populations

   https://doi.org/10.1093/g3journal/jkab192  

   Tung, Sudipta; Bakerlee, Christopher W; Phillips, Angela M; Nguyen Ba, Alex N; Desai, Michael M (June 2021, G3 Genes|Genomes|Genetics)

   Abstract Spontaneous whole-genome duplication, or autodiploidization, is a common route to adaptation in experimental evolution of haploid budding yeast populations. The rate at which autodiploids fix in these populations appears to vary across strain backgrounds, but the genetic basis of these differences remains poorly characterized. Here, we show that the frequency of autodiploidization differs dramatically between two closely related laboratory strains of Saccharomyces cerevisiae, BY4741 and W303. To investigate the genetic basis of this difference, we crossed these strains to generate hundreds of unique F1 segregants and tested the tendency of each segregant to autodiplodize across hundreds of generations of laboratory evolution. We find that variants in the SSD1 gene are the primary genetic determinant of differences in autodiploidization. We then used multiple laboratory and wild strains of S. cerevisiae to show that clonal populations of strains with a functional copy of SSD1 autodiploidize more frequently in evolution experiments, while knocking out this gene or replacing it with the W303 allele reduces autodiploidization propensity across all genetic backgrounds tested. These results suggest a potential strategy for modifying rates of spontaneous whole-genome duplications in laboratory evolution experiments in haploid budding yeast. They may also have relevance to other settings in which eukaryotic genome stability plays an important role, such as biomanufacturing and the treatment of pathogenic fungal diseases and cancers. 

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4. The element of Paaw in marsupials and the middle ear of Philander opossum (Linnaeus, 1758) (Didelphimorphia, Didelphidae)

   Wible, John R.; Shelley, Sarah L.; Belz, Carly (May 2021, Annals of Carnegie Museum)

   null (Ed.)

   A small piece of cartilage or bone, the element of Paaw, occurs in the tendon of the stapedius muscle in some extant marsupial and placental mammals. It has been nearly a century since the last comprehensive treatment of the distribution of the element of Paaw in mammals. The current report updates knowledge on this structure by synthesizing the subsequent literature and providing new observations of extant marsupials from the collections of the Section of Mammals, Carnegie Museum of Natural History, and two online resources for CT scanned data: DigiMorph.org and MorphoSource.org. We found an element of Paaw in some representatives of all seven extant marsupial orders: Didelphimorphia, Microbiotheria, Notoryctemorphia, Peramelemorphia, Paucituberculata, Dasyuromorphia, and Diprotodontia. In the first four orders, the element is substantial, longer than the long axis of the fenestra vestiuli (oval window), which holds the stapedial footplate; it is smaller than the long axis of the fenestra vestibuli in Paucituberculata and we do not have measures to report for the last two orders. In most marsupials examined, the element of Paaw contacts the petrosal behind the oval window, suggesting it functions as a sesamoid bone, increasing the lever arm of the stapedius muscle. Although there is some variability in the presence of the bone both between and within individual museum specimens, we interpret this as the result of preparation techniques rather than true variation. To place the element of Paaw in its anatomical context, we describe in detail the ear region and middle-ear auditory apparatus of the gray four-eyed opossum, Philander opossum (Linnaeus, 1758), a didelphid from Central and South America, based on a CT scanned specimen from Carnegie Museum of Natural History. It has an ossified element of Paaw with a volume greater than the stapes. Comparisons are made with petrosals of Didelphis marsupialis Linnaeus, 1758, and Monodelphis domestica (Wagner, 1842), also based on CT scanned specimens. 

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5. A family of olfactory receptors uniquely expanded in marsupial and monotreme genomes are expressed by a T cell subset also unique to marsupials and monotremes

   https://doi.org/10.1016/j.dci.2024.105149  

   Sampson, Jordan M; Morrissey, Kimberly A; Douek, Daniel C; Miller, Robert D (February 2024, Developmental & Comparative Immunology)

   Olfactory receptors (OR), expressed on olfactory neurons, mediate the sense of smell. Recently, OR have also been shown to be expressed in non-olfactory tissues, including cells of the immune system. An analysis of single-cell transcriptomes of splenocytes of the gray short-tailed opossum (Monodelphis domestica) found OR are expressed on a subset of T cells, the γμ T cells, that are unique to marsupials and monotremes. A majority of opossum γμ T cells transcriptomes contain OR family 14 transcripts, specifically, from the OR14C subfamily. Amongst the mammals, the OR14 gene family is expanded in the genomes of marsupials and monotremes, and rarer or absent in placental mammals. In summary, here we demonstrate the intriguing correlation that a family of OR genes, abundant in the genomes of marsupials and monotremes, are ectopically expressed in a particular subset of T cells unique to the marsupials and monotremes. 

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