Biology subjects

Klementz, B. C.

Publications and source records attributed to Klementz, B. C..

4 recordsLinked to original sources

bioRxiv2024

A chromosome-level genome of the giant vinegaroon Mastigoproctus giganteus exhibits the signature of pre-Silurian whole genome duplication

Within the arachnids, chromosome-level genome assemblies have greatly accelerated the understanding of gene family evolution and developmental genomics in key groups, such as spiders (Araneae), mites and ticks (Acariformes and Parasitiformes). Among other poorly studied arachnid orders that lack genome assemblies altogether are the clade Pedipalpi, which is comprised of three orders that form the sister group of spiders, which diverged over 400 Mya. We close this gap by generating the first chromosome-level assembly from a single specimen of the vinegaroon Mastigoproctus giganteus (Uropygi). We show that this highly complete genome retains plesiomorphic conditions for many gene families that have undergone lineage-specific derivations within the more diverse spiders. Consistent with the phylogenetic position of Uropygi, macrosynteny in the M. giganteus genome substantiates the signature of an ancient whole genome duplication.

genomics↗

bioRxiv2024

A novel expression domain of extradenticle underlies the evolutionary developmental origin of the chelicerate patella

Neofunctionalization of duplicated gene copies is thought to be an important process underlying the origin of evolutionary novelty and provides an elegant mechanism for the origin of new phenotypic traits. One putative case where a new gene copy has been linked to a novel morphological trait is the origin of the arachnid patella, a taxonomically restricted leg segment. In spiders, the origin of this segment has been linked to the origin of the paralog dachshund-2, suggesting that a new gene facilitated the expression of a new trait. However, various arachnid groups that possess patellae do not have a copy of dachshund-2, disfavoring the direct link between gene origin and trait origin. We investigated the developmental genetic basis for patellar patterning in the harvestman Phalangium opilio, which lacks dachshund-2. Here, we show that the harvestman patella is established by a novel expression domain of the transcription factor extradenticle. Leveraging this definition of patellar identity, we surveyed targeted groups across chelicerate phylogeny to assess when this trait evolved. We show that a patellar homolog is present in Pycnogonida (sea spiders) and various arachnid orders, suggesting a single origin of the patella in the ancestor of Chelicerata. A potential loss of the patella is observed in Ixodida. Our results suggest that the modification of an ancient gene, rather than the neofunctionalization of a new gene copy, underlies the origin of the patella. Broadly, this work underscores the value of comparative data and broad taxonomic sampling when testing hypotheses in evolutionary developmental biology.

evolutionary biology↗

bioRxiv2023

A taxon-restricted duplicate of Iroquois3 is required for patterning the spider waist

The chelicerate body plan is distinguished from other arthropod groups by its division of segments into two tagmata: the anterior prosoma ("cephalothorax") and the posterior opisthosoma ("abdomen"). Little is understood about the genetic mechanisms that establish the prosomal-opisthosomal (PO) boundary. To discover these mechanisms, we created high-quality genomic resources for the large-bodied spider Aphonopelma hentzi. We sequenced specific territories along the antero-posterior axis of developing embryos and applied differential gene expression analyses to identify putative regulators of regional identity. After bioinformatic screening for candidate genes that were consistently highly expressed in the posterior segments, we validated the function of highly ranked candidates in the tractable spider model Parasteatoda tepidariorum. Here, we show that an arthropod homolog of the Iroquois complex of homeobox genes is required for proper formation of the boundary between arachnid tagmata. The function of this homolog had not been previously characterized, because it was lost in the common ancestor of Pancrustacea, precluding its investigation in well-studied insect model organisms. Knockdown of the spider copy of this gene, which we designate as waist-less, in P. tepidariorum resulted in embryos with defects in the PO boundary, incurring discontinuous spider germ bands. We show that waist-less is required for proper specification of dorso-ventral identity in the segments that span the prosoma-opisthosoma boundary, which in adult spiders corresponds to the narrowed pedicel. Our results suggest the requirement of an ancient, taxon-restricted paralog for the establishment of the tagmatic boundary that defines Chelicerata.

evolutionary biology↗

bioRxiv2022

Dual functions of labial resolve the Hox logic of chelicerate head segments

Despite an abundance of gene expression surveys, comparatively little is known about Hox gene function in Chelicerata, with emphasis on the Hox logic of the anterior prosomal segments, which bear the mouthparts. Previous investigations of individual paralogs of labial (lab) and Deformed (Dfd) in the spider Parasteatoda tepidariorum have shown that these play a role in tissue maintenance of the pedipalpal segment (labial-1) and in patterning the first walking leg identity (Deformed-1), respectively. However, broader extrapolations of these data points across chelicerates are hindered by the existence of duplicated copies of Hox genes in arachnopulmonates (e.g., spiders and scorpions), which have resulted from an ancient whole genome duplication event. Here, we investigated the function of single-copy orthologs of lab in the harvestman Phalangium opilio, an exemplar of a lineage that was not subject of this whole genome duplication. Embryonic RNAi against lab resulted in homeotic transformations of pedipalps to chelicerae, as well as reduction and fusion of the pedipalpal segment with adjacent segments. To test for combinatorial function, we performed double knockdown of lab and Dfd, which results in homeotic transformation of both pedipalps and first walking legs into cheliceral identity, whereas the second walking leg is transformed into a pedipalpal identity. Taken together, these results elucidate a model for the Hox logic of head segments in Chelicerata. To substantiate the validity of this model, we additionally performed expression surveys for duplicated copies of lab and Dfd in scorpions and horseshoe crabs, toward understanding the genetic basis of a heteronomous prosoma. We show that repetition of morphologically similar appendages is correlated with uniform expression levels of the Hox genes lab and Dfd, irrespective of the number of gene copies.

developmental biology↗