Biology subjects

Piekarz, K. M.

Publications and source records attributed to Piekarz, K. M..

4 recordsLinked to original sources

bioRxiv2024

A change in cis-regulatory logic underlying obligate versus facultative muscle multinucleation in chordates

Vertebrates and tunicates are sister groups that share a common fusogenic factor, Myomaker (Mymk), that drives myoblast fusion and muscle multinucleation. Yet they are divergent in when and where they express Mymk. In vertebrates, all developing skeletal muscles express Mymk and are obligately multinucleated. In tunicates, Mymk is only expressed in post-metamorphic multinucleated muscles, but is absent from mononucleated larval muscles. In this study, we demonstrate that cis-regulatory sequence differences in the promoter region of Mymk underlie the different spatiotemporal patterns of its transcriptional activation in tunicates and vertebrates. While in vertebrates Myogenic Regulatory Factors (MRFs) like MyoD1 alone are required and sufficient for Mymk transcription in all skeletal muscles, we show that transcription of Mymk in post-metamorphic muscles of the tunicate Ciona requires the combinatorial activity of MRF/MyoD and Early B-Cell Factor (Ebf). This macroevolutionary difference appears to be encoded in cis, likely due to the presence of a putative Ebf binding site adjacent to predicted MRF binding sites in the Ciona Mymk promoter. We further discuss how Mymk and myoblast fusion might have been regulated in the last common ancestor of tunicates and vertebrates, for which we propose two models.

evolutionary biology↗

bioRxiv2024

A gene regulatory network for specification and morphogenesis of a Mauthner Cell homolog in non-vertebrate chordates

Transcriptional regulation of gene expression is an indispensable process in multicellular development, yet we still do not fully understand how the complex networks of transcription factors operating in neuronal precursors coordinately control the expression of effector genes that shape morphogenesis and terminal differentiation. Here we break down in greater detail a provisional regulatory circuit downstream of the transcription factor Pax3/7 operating in the descending decussating neurons (ddNs) of the tunicate Ciona robusta. The ddNs are a pair of hindbrain neurons proposed to be homologous to the Mauthner cells of anamniotes, and Pax3/7 is sufficient and necessary for their specification. We show that different transcription factors downstream of Pax3/7, namely Pou4, Lhx1/5, and Dmbx, regulate distinct "branches" of this ddN network that appear to be dedicated to different developmental tasks. Some of these network branches are shared with other neurons throughout the larva, reinforcing the idea that modularity is likely a key feature of such networks. We discuss these ideas and their evolutionary implications here, including the observation that homologs of all four transcription factors (Pax3/7, Lhx5, Pou4f3, and Dmbx1) are key for the specification of cranial neural crest in vertebrates.

developmental biology↗

bioRxiv2023

Specification and survival of post-metamorphic branchiomeric neurons in the hindbrain of a non-vertebrate chordate.

Tunicates are the sister group to the vertebrates, yet most species have a life cycle split between swimming larva and sedentary adult phases. During metamorphosis, larval neurons are largely replaced by adult-specific ones. Yet the regulatory mechanisms underlying this neural replacement remain largely unknown. Using tissue-specific CRISPR/Cas9-mediated mutagenesis in the tunicate Ciona, we show that orthologs of conserved hindbrain and branchiomeric neuron regulatory factors Pax2/5/8 and Phox2 are required to specify the "Neck", a compartment of cells set aside in the larva to give rise to cranial motor neuron-like neurons in the adult. Using bulk and single-cell RNAseq analyses, we also characterize the transcriptome of the Neck downstream of Pax2/5/8. Surprisingly, we find that Neck-derived adult ciliomotor neurons begin to differentiate in the larva, contrary to the long-held assumption that the adult nervous system is formed only after settlement and the death of larval neurons during metamorphosis. Finally, we show that manipulating FGF signaling during the larval phase alters the patterning of the Neck and its derivatives. Suppression of FGF converts Neck cells into larval neurons that fail to survive metamorphosis, while prolonged FGF signaling promotes an adult neural stem cell-like fate instead.

developmental biology↗

bioRxiv2023

Specification of distinct cell types in a sensory-adhesive organ for metamorphosis in the Ciona larva

The papillae of tunicate larvae contribute sensory, adhesive, and metamorphosis-regulating functions that are crucial for the biphasic lifestyle of these marine, non-vertebrate chordates. We have identified additional molecular markers for at least five distinct cell types in the papillae of the model tunicate Ciona, allowing us to further study the development of these organs. Using tissue-specific CRISPR/Cas9-mediated mutagenesis and other molecular perturbations, we reveal the roles of key transcription factors and signaling pathways that are important for patterning the papilla territory into a highly organized array of different cell types and shapes. We further test the contributions of different transcription factors and cell types to the production of the adhesive glue that allows for larval attachment during settlement, and to the processes of tail retraction and body rotation during metamorphosis. With this study, we continue working towards connecting gene regulation to cellular functions that control the developmental transition between the motile larva and sessile adult of Ciona.

developmental biology↗