# Comparing the expression patterns and differences of LOX and LOXL1 during the development of myodural bridge and ligamentum flavum

## TL;DR

This study explores how two tissues in the spine, the myodural bridge and ligamentum flavum, develop differently by comparing the roles of LOX and LOXL1 in their formation.

## Contribution

The study reveals that LOX and LOXL1 have differential expression patterns that influence structural differences between the myodural bridge and ligamentum flavum during development.

## Key findings

- The MDB and LF show distinct histological developmental patterns, with the MDB forming complete structures earlier than the LF.
- LOX and LOXL1 are critical for collagen and elastic fiber formation in both the MDB and LF.
- Differential expression of LOX and LOXL1 leads to variations in fiber composition and maturation timing, contributing to structural differences.

## Abstract

The ligamentum flavum (LF) is a passive stabilizing tissue that connects two adjacent vertebral arches and contributes to the enclosure the spinal canal, thereby closing the entire canal posteriorly. However, a gap exists at the posterior atlanto-occipital and atlanto-axial interspaces, where the LF is absent and replaced by the myodural bridge (MDB), which attaches to the spinal dura mater. The reasons for this anatomical difference and how it arises during development remain unclear. There are notable structural differences between MDB and LF. The MDB consists primarily of type I collagen fibers, while the LF contains both collagen and elastin fibers, with the latter comprising a higher proportion. This study speculates that LOX and LOXL1, as key regulators of fiber synthesis, play an essential role in the development of MDB and LF. Differences in the expression of LOX and LOXL1, which are involved in collagen and elastin cross-linking, may be one of the main factors underlying this structural divergence in the posterior cervical interspace. This study examined the cervicooccipital regions of rat embryos and young rats using histology, immunohistochemistry, and RT-qPCR to compare morphological and developmental differences between the MDB and LF. Additional experiments using the BAPN inhibitor were conducted to investigate the expression patterns and functional differences of LOX and LOXL1 during the development of the MDB and LF. Our aim is to clarify the developmental processes of the MDB and LF, identify the causes of structural differences in the posterior cervical interspaces, and reveal the molecular mechanisms regulating their formation. The conclusion of the current study as follows: ①The MDB and LF exhibit distinct histological developmental patterns: cells and fibers in the MDB align in an organized manner later than those in the LF, while the MDB forms its complete structures earlier than the LF. ②LOX and LOXL1 play critical roles in collagen and elastic fibers formation, mediating fiber synthesis in both the MDB and LF. ③Differential expression of LOX and LOXL1 during development leads to variations in fiber composition and maturation timing between the MDB and LF, contributing to their structural differences in the posterior cervical spinal interspace.