β4GalT7 is a transmembrane Golgi enzyme, encoded by B4GALT7, that plays a pivotal role in the proteoglycan linker region formation during proteoglycan biosynthesis. Defects in this enzyme give rise to a rare autosomal recessive form of Ehlers-Danlos syndrome (EDS), currently known as ‘spondylodysplastic EDS (spEDS-B4GALT7)’. This EDS subtype is mainly characterized by short stature, hypotonia and skeletal abnormalities, thereby illustrating its pleiotropic importance during human development. Insights into the pathogenic mechanisms underlying this disabling disease are very limited, in part due to the lack of a relevant in vivo model.

As the majority of mutations identified in patients with spEDS-B4GALT7 are hypomorphic, we generated zebrafish models with partial loss of B4galt7 function, including different knockdown (morphant) and mosaic knockout (crispant) b4galt7 zebrafish models and studied the morphologic, functional and molecular aspects in embryonic and larval stages.

Morphant and crispant zebrafish show highly similar morphological abnormalities in early development including a small, round head, bowed pectoral fins, short body-axis and mild developmental delay. Several craniofacial cartilage and bone structures are absent or strongly misshapen. In addition, the total amount of sulfated glycosaminoglycans is significantly diminished and particularly heparan and chondroitin sulfate proteoglycan levels are greatly reduced. We also show impaired cartilage patterning and loss of chondrocyte organization in a cartilage-specific Tg(Col2a1aBAC:mcherry) zebrafish reporter line. The occurrence of the same abnormalities in the different models confirms these are specifically caused by B4galt7 deficiency. A disturbed actin pattern, along with a lack of muscle tone, was only noted in morphants in which translation of b4galt7 was blocked.

In conclusion, we generated the first viable animal models for spEDS-B4GALT7, and show that in early development the human spEDS-B4GALT7 phenotype is faithfully mimicked in these zebrafish models. Our findings underscore a key role for β4GalT7 in early development of cartilage, bone and muscle. These models will lead to a better understanding of spEDS-B4GALT7 and can be used in future efforts focusing on therapeutic applications.

β4GalT7是由B4GALT7编码的跨膜高尔基酶，在蛋白聚糖生物合成过程中蛋白聚糖接头区域的形成中起着关键作用。该酶的缺陷会导致罕见的常染色体隐性遗传形式的Ehlers-Danlos综合征（EDS），目前称为“脊柱增生性EDS（spEDS- B4GALT7）”。这种EDS亚型的主要特征是身材矮小，肌张力低下和骨骼异常，从而说明了其在人类发育过程中的多效性重要性。对导致这种致残性疾病的致病机制的见解非常有限，部分原因是缺乏相关的体内模型。

由于在spEDS- B4GALT7患者中发现的大多数突变都是亚型的，因此我们生成了斑马鱼模型，其中部分B4galt7功能丧失，包括不同的敲除（突变体）和镶嵌敲除（脆性）b4galt7斑马鱼模型，并研究了形态，功能和分子方面在胚胎和幼虫阶段。

Morphant和脆皮斑马鱼在早期发育中表现出非常相似的形态异常，包括小而圆的头，弓形胸鳍，短身轴和适度的发育延迟。缺少几个颅面软骨和骨骼结构或畸形严重。另外，硫酸化糖胺聚糖的总量显着减少，尤其是乙酰肝素和软骨素硫酸盐蛋白聚糖的含量大大降低。我们还显示了软骨模式受损和软骨特异性Tg（Col2a1aBAC：mcherry）中软骨细胞组织的丧失斑马鱼记者专线。在不同模型中相同异常的发生证实了这些异常是由B4galt7缺乏引起的。被干扰的肌动蛋白格局，缺乏肌张力一起，在翻译morphants只注意到b4galt7被封堵。

总之，我们为spEDS- B4GALT7生成了第一个可行的动物模型，并表明在早期开发中，人的spEDS- B4GALT7表型忠实地模仿了这些斑马鱼模型。我们的发现强调了β4GalT7在软骨，骨骼和肌肉的早期发育中的关键作用。这些模型将使您对spEDS- B4GALT7有更好的了解，并可以用于将来的治疗应用中。