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1. The ETS-transcription factor Pointed is sufficient to regulate the posterior fate of the follicular epithelium

   https://doi.org/10.1242/dev.189787  

   Stevens, Cody A.; Revaitis, Nicole T.; Caur, Rumkan; Yakoby, Nir (November 2020, Development)

   null (Ed.)

   The Janus-kinase/Signal Transducers and Activators of Transcription (JAK/STAT) pathway regulates the anterior posterior axis of the Drosophila follicle cells. In the anterior, it activates the bone morphogenetic protein (BMP) signaling pathway through expression of the BMP ligand, decapentaplegic (dpp). In the posterior, JAK/STAT works with the epidermal growth factor receptor (EGFR) pathway to express the T-box transcription factor midline (mid). While MID is necessary in establishing the posterior fate of the egg chamber, we show that it is not sufficient to determine a posterior fate. The ETS-transcription factor pointed (pnt) is expressed in an overlapping domain to mid in the follicle cells. This study shows that pnt is upstream of mid, and it is sufficient to induce a posterior fate in the anterior end, which is characterized by the induction of mid, the prevention of the stretched cells formation, and the abrogation of border cells migration. We demonstrate that the anterior BMP signaling is abolished by PNT through dpp repression. However, ectopic DPP cannot rescue this repression, suggesting additional targets of PNT participate in the posterior fate determination. 

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2. Investigating the developmental onset of regenerative potential in the annelid Capitella teleta

   https://doi.org/10.1111/ivb.12411  

   Boyd, Alicia A; Seaver, Elaine C (December 2023, Invertebrate Biology)

   Abstract An animal's ability to regrow lost tissues or structures can vary greatly during its life cycle. The annelidCapitella teletaexhibits posterior, but not anterior, regeneration as juveniles and adults. In contrast, embryos display only limited replacement of specific tissues. To investigate when during development individuals ofC. teletabecome capable of regeneration, we assessed the extent to which larvae can regenerate. We hypothesized that larvae exhibit intermediate regeneration potential and demonstrate some features of juvenile regeneration, but do not successfully replace all lost structures. Both anterior and posterior regeneration potential of larvae were evaluated following amputation. We used several methods to analyze wound sites: EdU incorporation to assess cell proliferation; in situ hybridization to assess stem cell and differentiation marker expression; immunohistochemistry and phalloidin staining to determine presence of neurites and muscle fibers, respectively; and observation to assess re‐epithelialization and determine regrowth of structures. Wound healing occurred within 6 h of amputation for both anterior and posterior amputations. Cell proliferation at both wound sites was observed for up to 7 days following amputation. In addition, the stem cell markervasawas expressed at anterior and posterior wound sites. However, growth of new tissue was observed only in posterior amputations. Neurites from the ventral nerve cord were also observed at posterior wound sites. De novoashexpression in the ectoderm of anterior wound sites indicated neuronal cell specification, although the absence ofelavexpression indicated an inability to progress to neuronal differentiation. In rare instances, cilia and eyes re‐formed. Both amputations induced expanded expression of the myogenesis geneMyoDin preexisting tissues. Our results indicate that amputated larvae complete early, but not late, stages of regeneration, which indicates a gradual acquisition of regenerative ability inC. teleta. Furthermore, amputated larvae can metamorphose into burrowing juveniles, including those missing brain and anterior sensory structures. To our knowledge, this is the first study to assess regenerative potential of annelid larvae. 

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3. The FUSED LEAVES1‐ ADHERENT1 regulatory module is required for maize cuticle development and organ separation

   https://doi.org/10.1111/nph.16837  

   Liu, Xue; Bourgault, Richard; Galli, Mary; Strable, Josh; Chen, Zongliang; Feng, Fan; Dong, Jiaqiang; Molina, Isabel; Gallavotti, Andrea (August 2020, New Phytologist)

   Summary All aerial epidermal cells in land plants are covered by the cuticle, an extracellular hydrophobic layer that provides protection against abiotic and biotic stresses and prevents organ fusion during development.Genetic and morphological analysis of the classic maizeadherent1(ad1) mutant was combined with genome‐wide binding analysis of the maize MYB transcription factor FUSED LEAVES1 (FDL1), coupled with transcriptional profiling offdl1mutants.We show thatAD1encodes an epidermally‐expressed 3‐KETOACYL‐CoA SYNTHASE (KCS) belonging to a functionally uncharacterized clade of KCS enzymes involved in cuticular wax biosynthesis. Wax analysis inad1mutants indicates thatAD1functions in the formation of very‐long‐chain wax components. We demonstrate that FDL1 directly binds to CCAACC core motifs present inAD1regulatory regions to activate its expression. Over 2000 additional target genes of FDL1, including many involved in cuticle formation, drought response and cell wall organization, were also identified.Our results identify a regulatory module of cuticle biosynthesis in maize that is conserved across monocots and eudicots, and highlight previously undescribed factors in lipid metabolism, transport and signaling that coordinate organ development and cuticle formation. 

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4. Vertebral morphology in the tail-whipping common thresher shark, Alopias vulpinus

   https://doi.org/10.1098/rsos.231473  

   Knaub, Jamie L; Passerotti, Michelle; Natanson, Lisa J; Meredith, Tricia; Porter, Marianne (January 2024, Royal Society Open Science)

   Thresher sharks (Alopiasspp.) are characterized by an elongated, scythe-like caudal fin that is used in tail-whipping, a behaviour where the tail is thrown overhead to stun prey. Tail-whipping is performed via extreme dorsoventral bending of the vertebral column, and is dramatically different from lateral oscillatory motion used for swimming. Previous work has examined thresher shark vertebral morphology and mechanical properties, but in the context of swimming loads. Our goal was to assess centra morphometrics and microarchitecture for variations that may support extreme dorsoventral bending. We examined anterior and posterior body vertebrae from an embryo, five juvenile, and four adult thresher sharks using micro-computed tomography. We used principal component and landmark analyses to examine variables influencing vertebral morphology and mineral arrangement, respectively. We found that morphology and microstructure significantly varied across body regions and ontogeny. We hypothesize that anterior body vertebrae increase stability, while posterior body vertebrae support the caudal fin. Vertebral size and quantity of mineral structures (lamellae and nodes) increased across ontogeny, suggesting vertebrae adapt over development to support a larger body and tail. Based on our results, we hypothesize that thresher shark vertebrae vary in morphometrics and mineralization (amount and arrangement) supporting the mechanical needs for tail-whipping. 

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5. Serial block-face scanning electron microscopy of the tail tip of post-metamorphic amphioxus finds novel myomeres with odd shapes and unusually prominent sclerocoels

   Holland, Nicholas D.; Holland, Linda Z. (January 2024, Journal of Morphology)

   Serial block-face scanning electron microscopy of the tail tip of post-metamorphic amphioxus (Branchiostoma floridae) revealed some terminal myomeres never been seen before with other techniques. The morphology of these myomeres differed markedly from the chevron shapes of their more anterior counterparts. Histologically, these odd-shaped myomeres ranged from empty vesicles bordered by undifferentiated cells to ventral sacs composed of well-developed myotome, dermatome, and sclerotome. Strikingly, several of these ventral sacs gave rise to a nipple-like dorsal projection composed either entirely of sclerotome or a mixture of sclerotome and myotome. Considered as a whole, from posterior to anterior, these odd-shaped posterior myomeres suggested that their more substantial ventral part may represent the ventral limb of a chevron, while the delicate projection represents a nascent dorsal limb. This scenario contrasts with formation of chevron-shaped myomeres along most of the antero-posterior axis. Although typical chevron formation in amphioxus is surprisingly poorly studied, it seems to be attained by a dorso-ventral extension of the myomere accompanied by the assumption of a V-shape; this is similar to what happens (at least superficially) in developing fishes. Another unusual feature of the odd-shaped posterior myomeres of amphioxus is their especially distended sclerocoels. One possible function for these might be to protect the posterior end of the central nervous system from trauma when the animals burrow into the substratum. 

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