Biology subjects

Tucker, A. S.

Publications and source records attributed to Tucker, A. S..

7 recordsLinked to original sources

bioRxiv2024

FSP1 stem/progenitor cells are essential for TMJ growth and homeostasis

The temporomandibular joint (TMJ) is one of the most used joints in the body. Defects and wear in the cartilage of the joint, condyle, and fibrocartilage disc lie at the heart of many common TMJ disorders. During postnatal development the condyle acts as a growth centre for the mandible with cells moving as a conveyor belt away from the top of the condyle as they differentiate. The superficial layers of the condyle have been proposed to contain stem/progenitor populations to allow growth and maintain homeostasis. Here we have focused on the role of FSP1 (also known as S100a4), as a key fibroblast stem/progenitor marker for the condyle. Lineage tracing using FSP1-Cre;mTmG mice revealed that FSP1-positive cells were restricted to the superficial fibroblast zone giving rise to all layers of the condyle over time. The FSP1-expressing cells overlapped with other putative stem cell markers of the condyle, Gli1 and Scleraxis. BrdU pulse chase experiments highlighted that a subset of FSP1 fibrocartilage were label-retaining, suggesting that FSP1 labels a novel stem/progenitor cell population in the condyle. Destruction of FSP1-expressing cells by conditional diphtheria toxin activity in FSP1-Cre;DTA mice resulted in severe TMJ osteoarthritis (TMJOA) with loss of the cartilage structure. Lgr5 expressing cells in the superficial layer of the condyle, have previously been shown to create a Wnt inhibitory niche. FSP1 expression postnatally was associated with a reduction in canonical Wnt activity in the condyle. Importantly, constitutive activation of Wnt/{beta} catenin in FSP1 cells, led to a downregulation of FSP1 and progressive postnatal loss of TMJ condylar hyaline cartilage due to loss of the superficial stem/progenitor cells. These data demonstrate a novel role for FSP1-expressing cells in the superficial zone in growth and maintenance of the TMJ condylar cartilage and highlight the importance of regulating Wnt activity in this population.

developmental biology↗

bioRxiv2023

Tracking Cell Layer Contribution During Repair of the Tympanic Membrane

The tympanic membrane (or ear drum) is found at the interface between the middle ear and the external ear. The membrane is composed of three layers of different embryonic origin: an outer ectodermally-derived layer, a middle neural crest-derived fibroblast layer with contribution from the mesoderm-derived vasculature, and an inner endodermally-derived mucosal layer. These layers form a thin sandwich which is often perforated as a consequence of trauma, pressure changes, or middle ear inflammation. Usually, the tympanic membrane heals with minimal scarring, but in 6% of cases the perforation fails to heal leading to hearing loss, tinnitus and pain requiring surgery. How cells bridge the gap to close the perforation is an interesting question, as this needs to happen in the absence of an initial scaffold. Here we assess the contribution, timing, and interaction of the different layers of the membrane during repair in the mouse using markers and reporter mouse lines. We show that the ectodermal layer retracts after perforation, before proliferating away from the wound edge, with Keratin 5 basal cells migrating over the hole to bridge the gap. The mesenchymal and mucosal layers then use this scaffold to complete the repair, in tandem with changes in the vasculature. Finally, differentiation of the epithelium leads to formation of a scab that falls off. Our results reveal the dynamics and interconnections between the embryonic germ layers during repair and highlight how defects in healing may occur. Unearthing the complexities of TM healing is important as chronic TMP is a common clinical issue with limited treatment options.

molecular biology↗

bioRxiv2021

Getting out of a mammalian egg: the egg tooth and caruncle of the echidna

In the short-beaked echidna, Tachyglossus aculeatus, after an initial period of in utero development, the egg is laid in the pouch and incubated for 10 days. During this time, the fetuses develop an egg tooth and caruncle to help them hatch. However, there are only a few historical references that describe the development of the monotreme egg tooth. Using unprecedented access to echidna pre- and post-hatching tissues, the egg tooth and caruncle were assessed by micro-CT, histology and immunofluorescence, to map the changes at the morphological and molecular level. Unlike mammalian tooth germs that develop by invagination of a placode, the echidna egg tooth developed by evagination, similar to that of the first teeth in some reptiles. The egg tooth ankylosed to the premaxilla, rather than forming a mammalian thecodont attachment, with loss of the egg tooth post-hatching associated with high levels of odontoclasts, and apoptosis. The caruncle formed as a separate mineralisation from the adjacent nasal capsule, and as observed in birds and turtles, the nasal region epithelium expressed markers of cornification. Together, this highlights that the monotreme egg tooth shares many similarities with reptilian teeth, suggesting that this tooth is conserved from a common ancestor of mammals and reptiles.

evolutionary biology↗

bioRxiv2021

Collateral damage: Identification and characterisation of spontaneous mutations causing deafness from a targeted knockout programme

Mice carrying targeted mutations are important for investigating gene function and the role of genes in disease, but the process of culturing embryonic stem cells during the making of a targeted allele offers opportunities for spontaneous mutations to arise. Identifying spontaneous mutations relies on the detection of phenotypes segregating independently of targeted alleles, and many phenotypes are easy to miss if not specifically looked for. Here we present data from a large, targeted knockout programme in which mice were analysed through a phenotyping pipeline. Twenty-five lines out of 1311 displayed different deafness phenotypes that did not segregate with the targeted allele. We have identified 8 different mutations causing deafness in 16 of these 25 lines and characterised the resulting phenotypes. Our data show that spontaneous mutations with observable effects on phenotype are a common side effect of intensive breeding programmes, including those underlying targeted mutation programmes.

genetics↗

bioRxiv2021

Salted roads lead to edema and reduced locomotor function in wood frogs

Human activities have caused massive losses of natural populations across the globe. Like many groups, amphibians have experienced substantial declines worldwide, driven by environmental changes such as habitat conversion, pollution, and disease emergence. Each of these drivers is often found in close association with the presence of roads. Here we report a novel consequence of roads affecting an amphibian native to much of North America, the wood frog (Rana sylvatica). Across 38 populations distributed from southern to central New England, we found that adult wood frogs living adjacent to roads had higher incidence and severity of edema (bloating caused by fluid accumulation) during the breeding season than frogs living away from the influence of roads. This effect was best explained by increased conductivity of breeding ponds, caused by runoff pollution from road salt used for de-icing. Edema severity was negatively correlated with locomotor performance in more northerly populations. Interestingly, northern populations experience more intense winters, which tends to result in more de-icing salt runoff and increased energetic demands associated with overwintering cryoprotection needs. Thus, this emerging consequence of roads appears to impose potential fitness costs associated with locomotion, and these effects might be most impactful on populations living in regions where de-icing is most intense.

ecology↗

bioRxiv2020

A cranio-incudo joint as the solution to early birth in marsupials and monotremes

Mammals articulate their jaws using a novel joint between the dentary and squamosal bones. In eutherian mammals, this joint forms in the embryo, supporting feeding and vocalisation from birth. In contrast, marsupials and monotremes exhibit extreme altriciality and are born before the bones of the novel mammalian jaw joint form. These mammals need to rely on other mechanisms to allow them to feed. Here we show that this vital function is carried out by the earlier developing, cartilaginous incus of the middle ear, abutting the cranial base to form a cranio-mandibular articulation. The nature of this articulation varies between monotremes and marsupials, with monotremes retaining a double articulation, similar to that described in the fossil mammaliaform, Morganucodon, while marsupials use a versican rich matrix to stabilise the jaw against the cranial base. These findings provide novel insight into the evolution of mammals and the relationship between the jaw and ear.

developmental biology↗

bioRxiv2020

The TMJ disc is a common ancestral feature in all mammals, as evidenced by the presence of a rudimentary disc during monotreme development.

The novel mammalian jaw joint, known in humans as the temporomandibular joint or TMJ, is cushioned by a fibrocartilage disc. This disc is secondarily absent in therian mammals that have lost their dentition, such as giant anteaters and some baleen whales. The disc is also absent in all monotremes. However, it is not known if the absence in monotremes is secondary to the loss of dentition, or if it is an ancestral absence. We use museum held platypus and echidna histological sections to demonstrate that the developing monotreme jaw joint forms a disc primordium that fails to mature and become separated from the mandibular condyle. We then show that monotreme developmental anatomy is similar to that observed in transgenic mouse mutants with reduced musculature. We therefore suggest that the absence of the disc on monotremes is a consequence of the changes in jaw musculature associated with the loss of adult teeth. Taken together, these data indicate that the ancestors of extant monotremes likely had a jaw joint disc, and that the disc evolved in the last common ancestor or all mammals.

developmental biology↗