TLX-1 AND TLX-3 HOMEOBOX GENE-EXPRESSION IN CRANIAL SENSORY GANGLIA AND HINDBRAIN OF THE CHICK-EMBRYO - MARKERS OF PATTERNED CONNECTIVITY

Recent evidence suggests that in vertebrates the formation of distinct neuronal cell types is controlled by specific families of homeodomain transcription factors. Furthermore, the expression domains of a numbe r of these genes correlates with functionally integrated neuronal popu lations. We have isolated two members of the divergent T-cell leukemia translocation (HOX11/Tlx) homeobox gene family from chick, Tlx-1 and Tlx-3, and show that they are expressed in differentiating neurons of both the peripheral and central nervous systems. In the peripheral ner vous system, Tlx-1 and Tlx-3 are expressed in overlapping domains with in the placodally derived components of a number of cranial sensory ga nglia. Tlx-3, unlike Tlx-1, is also expressed in neural crest-derived dorsal root and sympathetic ganglia. In the CNS, both genes are expres sed in longitudinal columns of neurons at specific dorsoventral levels of the hindbrain. Each column has distinct anterior and/or posterior limits that respect inter-rhombomeric boundaries. Tlx-3 is also expres sed in D2 and D3 neurons of the spinal cord. Tlx-1 and Tlx-3 expressio n patterns within the peripheral and central nervous systems suggest t hat Tlx proteins may be involved not only in the differentiation and/o r survival of specific neuronal populations but also in the establishm ent of neuronal circuitry. Furthermore, by analogy with the LIM genes, Tlx family members potentially define sensory columns early within th e developing hindbrain in a combinatorial manner.