Evolution of shell loss in Opisthobranch gastropods: sea hares (Opisthobranchia, Anaspidea) as a model system

Due to the advantages of the hard, calcifying shell, the Mollusca are one of the most successful animal phyla. The shell forms during embryonic and larval development; however, many molluscan groups have a highly reduced shell or have lost it completely as development and maturation proceeds. These major developmental transitions in shell morphology frequently correlate with ecological transitions (e.g. diet change/change from planktonic to bethic existence pre- and post-metamorphosis, respectively). While shell loss may leave an organism vulnerable to predation, many have evolved alternative means to deter predators. Here we compare and contrast the post-hatching larval development and shell growth through the use of the life cycle staging of Bursatella leachii and Aplysia californica in laboratory settings. The larval developmental sequence of B. leachii is indistinguishable to other previously described plankotrophic aplysiids. However, the growth rate and size of B. leachii larvae differ from A. californica larvae substantially, growing relatively faster and larger by an average of 10 μm. We also describe the life cycle of B. leachii in context of the development of the larval shell and its subsequent loss in post-metamorphic stages. Comparison of the Stage 6 shells, both whole and cross-sections, of A. californica and B. leachii through the use of SEM showed little difference in morphology. These data indicate that we have established a reliable culturing technique for B. leachii in the laboratory which makes this species can be easily amendable to experimentation at all developmental stages. Metamorphosis and shell loss/reduction in A. californica and B. leachii highlight the differences of the developmental program of both species, which reflects its complexity at a molecular, cellular and organismal level. The comparison of sea hares is an ideal evolutionary comparative model system for the loss of acquired features. Molluscan biomineralization has been of broad scientific interest ranging from paleontological (molluscan shells provide one of the best fossil records for a metazoan phylum), to material science (perl and nacre formation) research. Although the properties (i.e. evolutionary origins, construction, patterning, physical) of the molluscan shell have been studied for decades, the underlying molecular and cellular mechanisms of how shell formation occurs are just recently surfacing with the identification of a handful of shell forming proteins. It is now known that one of the main components involved in the control of shell synthesis are the proteinaceous constituents of the shell matrix with in different kinds of functions (i.e. cell signaling, enzymatic activities), which are contributing to the diversity of different shell types in gastropod, bivalve and scaphopod molluscs. However, the differential gene expression and regulation within the mantle still remains unknown. Here we relate the developmental expression of eleven genes present in the mantle, the organ responsible for the secretion of the shell, in the sea hare Aplysia californica (Opisthobranchia, Anaspidea). Six genes that show very little changes in expression levels (Cluster 1). Three genes shows increased levels of expression during trochophore and veliger stages which then decrease in metamorphic stages (Cluster 3). Two genes had peptide-like profiles, genes that low expression during early development but have high expression levels late in development (Cluster 4). All eleven genes display dynamic spatial and temporal expression profiles within the larval shell field and mantle for the construction of the larval shell. The expression data from these eleven genes reflect the regulatory complexity that underlies the molluscan shell construction during larval stages. While the fabrication of the shell is taking place, the incorporation of both ancient and novel genes during also suggest that there is a core set of mantle-secreting genes for shell construction was provided by a shared metazoan ancestor to produce the range of molluscan shell types we see today

Patching the Leaks: Revitalizing and Reimagining the STEM Pipeline.

We identify problematic areas throughout the Science, Technology, Engineering and Mathematics (STEM) pipeline that perpetuate racial disparities in academia. Distinct ways to curtail these disparities include early exposure and access to resources, supportive mentoring networks and comprehensive training programs specifically for racially minoritized students and trainees at each career stage. These actions will revitalize the STEM pipeline

Ablation of Sam50 is associated with fragmentation and alterations in metabolism in murine and human myotubes

The sorting and assembly machinery (SAM) Complex is responsible for assembling β‐barrel proteins in the mitochondrial membrane. Comprising three subunits, Sam35, Sam37, and Sam50, the SAM complex connects the inner and outer mitochondrial membranes by interacting with the mitochondrial contact site and cristae organizing system complex. Sam50, in particular, stabilizes the mitochondrial intermembrane space bridging (MIB) complex, which is crucial for protein transport, respiratory chain complex assembly, and regulation of cristae integrity. While the role of Sam50 in mitochondrial structure and metabolism in skeletal muscle remains unclear, this study aims to investigate its impact. Serial block‐face‐scanning electron microscopy and computer‐assisted 3D renderings were employed to compare mitochondrial structure and networking in Sam50‐ deficient myotubes from mice and humans with wild‐type (WT) myotubes. Furthermore, autophagosome 3D structure was assessed in human myotubes. Mitochondrial metabolic phenotypes were assessed using Gas Chromatography‐Mass Spectrometry‐based metabolomics to explore differential changes in WT and Sam50‐deficient myotubes. The results revealed increased mitochondrial fragmentation and autophagosome formation in Sam50‐deficient myotubes compared to controls. Metabolomic analysis indicated elevated metabolism of propanoate and several amino acids, including ß‐ Alanine, phenylalanine, and tyrosine, along with increased amino acid and fatty acid metabolism in Sam50‐deficient myotubes. Furthermore, impairment of oxidative capacity was observed upon Sam50 ablation in both murine and human myotubes, as measured with the XF24 Seahorse Analyzer. Collectively, these findings support the critical role of Sam50 in establishing and maintaining mitochondrial integrity, cristae structure, and mitochondrial metabolism. By elucidating the impact of Sam50‐deficiency, this study enhances our understanding of mitochondrial function in skeletal muscle

Epithelial morphogenesis in the perinatal mouse uterus

AbstractBackgroundThe uterus is the location where multiple events occur that are required for the start of new life in mammals. The adult uterus contains endometrial or uterine glands that are essential for female fertility. In the mouse, uterine glands are located in the lateral and anti-mesometrial regions of the uterine horn. Previous 3D-imaging of the adult uterus, its glands, and implanting embryos has been performed by multiple groups, using fluorescent microscopy. Adenogenesis, the formation of uterine glands, initiates after birth. Recently, we created a 3D-staging system of mouse uterine gland development at postnatal time points, using light sheet fluorescent microscopy. Here, using a similar approach, we examine the morphological changes in the epithelium of the perinatal mouse uterus.ResultsThe uterine epithelium exhibits mesometrial-antimesometrial (dorsoventral) patterning as early as three days after birth (P3), marked by the presence of the mesometrially-positioned developing uterine rail. Uterine gland buds are present beginning at P4. Novel morphological epithelial structures, including a ventral ridge and uterine segments were identified.ConclusionsThe perinatal mouse uterine luminal epithelium develops mesometrial-antimesometrial (dorsal-ventral) morphologies at 3-4 days post-partum. Between 5-6 days post-partum uterine epithelial folds form, defining alternating left-right segments.Bullet pointsMorphological patterning events in the perinatal uterine epithelium are not well described.Light sheet microscopy was used to generate volumetric reconstructions of the perinatal mouse uterine epithelium.At postnatal day 3 (P3), the uterine epithelium shows the first signs of dorsoventral pattern, with the presence of the forming mesometrially-positioned uterine rail.The first morphological indication of uterine adenogenesis begins at P4.Novel morphological structures were identified from volumetric reconstructions, including the presence of a ventral ridge (another sign of dorsoventral pattern) and uterine segmentation.</jats:sec

Morphology and development of the Portuguese man of war,<i>Physalia physalis</i>

AbstractThe Portuguese man of war,Physalia physalis, is a siphonophore that uses a gas-filled float as a sail to catch the wind. It is one of the most conspicuous, but poorly understood members of the pleuston, a community of organisms that occupy a habitat at the sea-air interface. The development, morphology, and colony organization ofP. physalisis very different from all other siphonophores. Here, we propose a framework for homologizing the axes with other siphonophores, and also suggest that the tentacle bearing zooids should be called tentacular palpons. We also look at live and fixed larval and non-reproductively mature juvenile specimens, and use optical projection tomography to build on existing knowledge about the morphology and development of this species. Previous descriptions ofP. physalislarvae, especially descriptions of budding order, were often framed with the mature colony in mind. However, we use the simpler organization of larvae and the juvenile specimens to inform our understanding of the morphology, budding order, and colony organization in the mature specimen. Finally, we review what is known about the ecology and lifecyle ofP. physalis.</jats:p

Morphology and development of the Portuguese man of war, Physalia physalis

AbstractThe Portuguese man of war, Physalia physalis, is one of the most conspicuous, but poorly understood members of the pleuston, a community of organisms that occupy a habitat at the sea-air interface. Physalia physalis is a siphonophore that uses a gas-filled float as a sail to catch the wind. The development, morphology, and colony organization of P. physalis is very different from all other siphonophores. Here, we look at live and fixed larval and juvenile specimens, and use optical projection tomography to build on existing knowledge about the morphology and development of this species. We also propose a framework for homologizing the axes with other siphonophores, and also suggest that the tentacle bearing zooids should be called tentacular palpons. Previous descriptions of P. physalis larvae, especially descriptions of budding order, were often framed with the mature colony in mind. However, we use the simpler organization of larvae and the juvenile specimens to inform our understanding of the morphology, budding order, and colony organization in the mature specimen. Finally, we review what is known about the ecology and lifecycle of P. physalis.</jats:p

A three-dimensional staging system of mouse endometrial gland morphogenesis

AbstractEndometrial or uterine glands secrete substances essential for uterine receptivity to the embryo, implantation, conceptus survival, development, and growth. Adenogenesis is the process of gland formation within the stroma of the uterus that occurs after birth. In the mouse, uterine gland formation initiates at postnatal day (P) 5. Subsequently, the developing uterine glands invade into the adjacent stroma. Mouse uterine gland morphology is poorly understood because it is based on two-dimensional (2D) histological observations. To more fully describe uterine gland morphogenesis, we generated three-dimensional (3D) models of postnatal uterine glands from P0 to P21, using light sheet microscopy. At birth (P0), there were no glands. At P8, we found bud- and teardrop-shaped epithelial invaginations. By P11, the forming glands were elongated epithelial tubes. By P21, the elongated tubes had a sinuous morphology. These morphologies are homogeneously distributed along the anterior-posterior axis of the uterus. To facilitate uterine gland analyses, we propose a novel 3D staging system of uterine gland morphology during postnatal development in the mouse. We define 6 stages: Stage 0: Aglandular, Stage 1: Bud, Stage 2: Teardrop, Stage 3: Elongated, Stage 4: Sinuous, and Stage 5: Primary Branches. This staging system provides a standardized key to assess and quantify uterine gland morphology that can be used for studies of uterine gland development and pathology. In addition, our studies suggest that gland formation initiation occurs during P8 and P11. However, between P11 and P21 gland formation initiation stops and all glands elongate and become sinuous.</jats:p

Comparative analysis of early ontogeny in Bursatella leachii and Aplysia californica

Opisthobranch molluscs exhibit fascinating body plans associated with the evolution of shell loss in multiple lineages. Sea hares in particular are interesting because Aplysia californica is a well-studied model organism that offers a large suite of genetic tools. Bursatella leachii is a related tropical sea hare that lacks a shell as an adult and therefore lends itself to comparative analysis with A. californica. We have established an enhanced culturing procedure for B. leachii in husbandry that enabled the study of shell formation and loss in this lineage with respect to A. californica life staging