HOXA9 is a human protein encoded in the HOXA9 gene, which is important in maintaining stem cell populations and guiding their differentiation in mammalian development, where there are three distinct stages of erythrocyte formation with adult erythrocyte being the most common.
From these results, it appears that HOXA9 is important in maintaining HSC populations, as well as guiding their differentiation, especially towards myeloid (erythroid and granulocyte) lineages. 
