Question: what is the function of the proteins secreted by cells of the ventral midline of the spinal cord
[{'answer': 'patterning the ventral axis', 'provenance': [{'wikipedia_id': '208900', 'title': 'Neural tube', 'start_paragraph_id': 25, 'start_character': 366, 'end_paragraph_id': 25, 'end_character': 393, 'bleu_score': 1.0, 'section': 'Section::::Dorsal-ventral patterning.\n'}]}, {'provenance': [{'wikipedia_id': '208900', 'title': 'Neural tube', 'start_paragraph_id': 25, 'start_character': 0, 'end_paragraph_id': 25, 'end_character': 771, 'bleu_score': 0.9828310228624961, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 12498672373347732342}, 'section': 'Section::::Dorsal-ventral patterning.\n'}]}]