Characterisation of lmx1b paralogues in zebrafish reveals divergent roles in skeletal, kidney, and muscle development

LMX1B, a LIM-homeodomain family transcription factor, plays critical roles in the development of multiple tissues, including limbs, eyes, kidneys, brain, and spinal cord. Mutations in the human LMX1B gene cause the rare autosomal-dominant disorder, Nail-patella syndrome which affects development of limbs, eyes, brain, and kidneys. In zebrafish, lmx1b has two paralogues: lmx1ba and lmx1bb. While lmx1b morpholino data exists, stable mutants were previously lacking. Here we describe the characterisation of lmx1b stable mutant lines, with a focus on development of tissues which are affected in Nail-patella syndrome. We demonstrate that the lmx1b paralogues have divergent developmental roles in zebrafish, with lmx1ba affecting skeletal and neuronal development, and lmx1bb affecting renal development. The double mutant, representing loss of both paralogues (lmx1b dKO) showed a stronger phenotype which included additional defects to trunk muscle patterning, and a failure to fully inflate the notochord leading to a dramatic reduction in body length. Overall, these mutant lines demonstrate the utility of zebrafish for modelling Nail- patella syndrome and describe a previously undescribed role for lmx1b in notochord cell inflation. SUMMARY STATEMENTZebrafish lmx1ba and lmx1bb knockout lines exhibit paralogue-specific roles in cartilage, renal, muscle, and notochord development, establishing zebrafish as a viable model for dissecting LMX1B- related pathologies such as Nail-patella syndrome.