Université de Rouen Normandie

The quadriceps femoris (QF) is classically described as a four-headed muscle. However, anatomical and radiological studies increasingly reveal supernumerary heads and tendon stratifications, challenging this concept.

This review synthesizes current cadaveric, imaging, and surgical evidence to propose a reclassification of QF as a multiceps femoris (MF). A five-type tendon-based classification system is introduced, reflecting distinct morphological variants and layering complexities.

An extensive review of anatomical dissection studies, radiological investigations (MRI and ultrasound), and clinical reports were conducted to evaluate morphological variability and its implications for tendon harvesting and surgical access.

Accessory heads such as the tensor vastus intermedius and caput tertium were present in over 60 % of cases, often contributing to distinct layers within the quadriceps femoris tendon (QFT). These configurations influence graft length, harvesting safety, and radiological interpretation. Misidentification of these structures may result in surgical complications or diagnostic errors. Functional and evolutionary analogies with other multiceps systems support the anatomical independence of these heads.

The MF model aligns with modular systems seen in the triceps surae and biceps femoris. Recognizing QF as MF offers a more anatomically accurate and clinically relevant framework. Adoption of updated terminology and imaging protocols may improve diagnosis, reduce surgical risk, and support personalized interventions.

Circular RNAs (circRNAs) have recently garnered significant attention due to their emerging regulatory roles across eukaryotic organisms. These non-coding RNA molecules are generated through a non-canonical back-splicing mechanism that covalently joins the 5' and 3' ends, resulting in a closed-loop structure. Although the complete functional landscape of circRNAs remains to be elucidated, advances in RNA sequencing technologies and computational biology have accelerated their identification and functional annotation in both plant and mammalian systems. CircRNAs are increasingly implicated in the regulation of key cellular and metabolic processes, including transcription, translation, protein-protein interactions, cellular proliferation, development, and stress responses, thereby contributing to homeostasis and survival. In this study, we present a comprehensive overview of circRNA biogenesis, structural features, biological roles, and bioinformatic tools used for their prediction in eukaryotes. However, no prior studies have systematically characterized circRNAs in microalgae. To address this gap, we analyzed RNA-seq datasets from three phylogenetically distinct microalgal species (e.g., Chlamydomonas reinhardtii, Dunaliella salina, and Phaeodactylum tricornutum) using the CIRI2 pipeline to identify putative circRNAs. Our analysis revealed candidate circRNAs potentially involved in essential biological pathways, including RNA transcription regulation, mRNA splicing, translational control, chlorophyll function, cytochrome c maintenance, and various post-transcriptional and post-translational modifications. These findings offer novel insights into the regulatory landscape of circRNAs in microalgal species and lay the groundwork for future functional investigations.