Conserved and divergent aspects of leg development in Tardigrada

Presenter Information

Mandy Game
Frank W. Smith

Faculty Sponsor

Frank W. Smith

Faculty Sponsor College

College of Arts and Sciences

Faculty Sponsor Department

Biology

Location

SOARS Virtual Conference

Presentation Website

https://unfsoars.domains.unf.edu/2021/posters/conserved-and-divergent-aspects-of-leg-development-in-tardigrada/

Keywords

SOARS (Conference) (2021 : University of North Florida) – Archives; SOARS (Conference) (2021 : University of North Florida) – Posters; University of North Florida -- Students -- Research – Posters; University of North Florida. Office of Undergraduate Research; University of North Florida. Graduate School; College students – Research -- Florida – Jacksonville – Posters; University of North Florida – Undergraduates -- Research – Posters; University of North Florida. Department of Biology -- Research – Posters; Honorable Mention Award

Abstract

Honorable Mention Winner

Legs are a defining characteristic of Panarthropoda, a lineage of animals that includes Arthropoda, Onychophora, and Tardigrada. Arthropod and onychophoran leg development are well studied, but little is known about the leg development of tardigrades. Our recent investigations revealed several intriguing examples about the conservation and diversification of downstream developmental mechanisms in the appendages of the tardigrade Hypsibius exemplaris. In arthropods and onychophorans, the leg gap genes homothorax, extradenticle, dachshund, and Distal-less regulate appendage growth and specify proximodistal leg identities. However, in tardigrades the leg gap genes are not expressed in the regionalized patterns that are seen in onychophorans and arthropods. Dachshund is missing from the tardigrade genome. A distal leg patterning network is active downstream of Distal-less in arthropods and many features of this network are conserved in onychophorans. However, of the distal leg patterning genes thus far investigated, only aristaless is expressed in all leg buds during tardigrade development. Here, we investigate upstream components of tardigrade leg development. In arthropods, wnt1 activates Sp6-9 to specify ventral appendages. This mechanism is most likely conserved in onychophorans. We identified orthologs of two Sp genes in Hypsibius expemplaris, including two copies of Sp6-9. We did not find a buttonhead ortholog, suggesting that this gene is missing from the tardigrade genome. While Sp6-9 is expressed strongly in the developing legs of tardigrades, wnt1 is missing from the tardigrade genome. Placed in a phylogenetic context, our results reveal that leg development has been secondarily simplified in Tardigrada in association with miniaturization.

Comments

Audio Presentation Transcript:

Hi there. My name is Mandy Game and I am an undergrad at the University of North Florida where I study body plan evolution in tardigrades with Dr. Frank Smith. My research is focused on tardigrade appendages, the genes that pattern them, and how they got so small. The first thing I looked at in tardigrades were the leg gap genes, and through that study found that tardigrades are missing a very important gene called dachshund, which patterns intermediate regions of the appendages in other animals. This led us to the conclusion that tardigrades have lost an intermediate region of their appendages, and have a reduced proximodistal axis. To learn more about leg gap genes in tardigrades, we published a paper about it this past summer, and the information to find that paper is right here. Next, I looked at the distal components of leg patterning. I discovered that while many of these distal patterning genes found in tardigrades’ closest relatives are present in tardigrades, the expression patterns of those genes are very different in tardigrade legs. In fact, only this gene aristaless appears in all four distal tips of tardigrade appendages during the developmental stages we have investigated. This suggests that the distal patterning network has also been secondarily simplified in tardigrade legs. More recently I have been focusing on upstream components of tardigrade leg patterning. In other animals, the gene SP6-9 is an activator of Distal-less – this important leg-gap gene. My insitu results show a pattern that is very similar to that of distal-less at these developmental stages in tardigrades. Other components to consider are the wnt genes. Here I have confocal images of wnt5 and wnt16b. These experiments were performed by my labmate Raul Chavarria, he is a really cool scientist and you should go check out his poster about wnt genes in tardigrades. Wnt5 shows broad expression across each developing tardigrade limb, while wnt16 is expressed in these ventral-leg stripes. All of these patterns are consistent with what is found in other animals with appendages, but we will need to do more experiments to determine whether these genes are truly upstream in the leg patterning network of tardigrades. So, as you can see, while many of these genes known for patterning the appendages of other animals are present in the genomes of tardigrades, the expression patterns of the genes tend to be very different. The predicted upstream components so far appear to be more conserved in their expression, but things get messy when we start looking at the predicted downstream components.

This supports the hypothesis that tardigrade appendages are secondarily simplified beyond just their reduced proximodistal axis. In the future, we hope to use RNAi to determine the functions of these genes, and to see if interactions between genes such as Sp6-9 and Distal-less, are conserved in tardigrade legs.

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