May be required for the coordinated crosstalk of factors involved in the maintenance of energy homeostasis, possibly by regulating the transcription of specific factors involved in energy balance. Detected as early as embryonic stage 10.5 dpc in the ventral mesencephalon, metencephalon, and ventral neural tube and continues to be expressed from this embryonic stage onward, predominantly in the ventral neural tube and the mid/hindbrain boundary region. In the later stages, 12.5 to 16.5 dpc, expression in the brain is detected more specifically in the pons and medulla oblongata. Autoregulated by a negative-feedback mechanism in the ventral midbrain and a positive-feedback mechanism in the midbrain-hindbrain boundary region and the eyes. Homozygous knockout mice for Sax2 exhibit growth retardation starting immediately after birth and leading to premature death within the first 3 weeks postnatal. Mice do not exhibit any obvious abnormal behavior or motor skills. All mice show normal suckling behavior, but at 2 or 3 days prior to their death, they become lethargic and show signs of wasting. The few homozygous animals surviving to adulthood are fertile, but all the offspring from homozygous intermatings die within 4 days postnatally (PubMed:14645517, PubMed:17879320). At 2 weeks postnatal days, mice lack subcutaneous fat and intra-abdominal epididymal and mesenteric white adipose tissue (WAT) (PubMed:17879320). Belongs to the NK-1 homeobox family.