Teashirt-3, a novel regulator of muscle differentiation, associates with BRG1-associated factor 57 (BAF57) to inhibit myogenin gene expression.

In adult muscles and under normal physiological conditions, satellite cells are found in a quiescent state but can be induced to enter the cell cycle by signals resulting from exercise, injury-induced muscle regeneration, or specific disease states. Once activated, satellite cells proliferate, self-renew, and differentiate to form myofibers. In the present study, we found that the zinc finger-containing factor Teashirt-3 (TSHZ3) was expressed in quiescent satellite cells of adult mouse skeletal muscles. We showed that following treatment with cardiotoxin TSHZ3 was strongly expressed in satellite cells of regenerating muscles. Moreover, immunohistochemical analysis indicated that TSHZ3 was expressed in both quiescent and activated satellite cells on intact myofibers in culture. TSHZ3 expression was maintained in myoblasts but disappeared with myotube formation. In C2C12 myoblasts, we showed that overexpression of Tshz3 impaired myogenic differentiation and promoted the down-regulation of myogenin (Myog) and up-regulation of paired-box factor 7 (Pax7). Moreover, knockdown experiments revealed a selective effect of Tshz3 on Myog regulation, and transcriptional reporter experiments indicated that TSHZ3 repressed Myog promoter. We identified the BRG1-associated factor 57 (BAF57), a subunit of the SWI/SNF complex, as a partner of TSHZ3. We showed that TSHZ3 cooperated with BAF57 to repress MYOD-dependent Myog expression. These results suggest a novel mechanism for transcriptional repression by TSHZ3 in which TSHZ3 and BAF57 cooperate to modulate MyoD activity on the Myog promoter to regulate skeletal muscle differentiation.

Teashirt 3 regulates development of neurons involved in both respiratory rhythm and airflow control.

Neonatal breathing in mammals involves multiple neuronal circuits, but its genetic basis remains unclear. Mice deficient for the zinc finger protein Teashirt 3 (TSHZ3) fail to breathe and die at birth. Tshz3 is expressed in multiple areas of the brainstem involved in respiration, including the pre-Bötzinger complex (preBötC), the embryonic parafacial respiratory group (e-pF), and cranial motoneurons that control the upper airways. Tshz3 inactivation led to pronounced cell death of motoneurons in the nucleus ambiguus and induced strong alterations of rhythmogenesis in the e-pF oscillator. In contrast, the preBötC oscillator appeared to be unaffected. These deficits result in impaired upper airway function, abnormal central respiratory rhythm generation, and altered responses to pH changes. Thus, a single gene, Tshz3, controls the development of diverse components of the circuitry required for breathing.

LIFR beta plays a major role in neuronal identity determination and glial differentiation in the mouse facial nucleus.

In the hindbrain, generation of the facial nucleus involves complex developmental processes that will lead to the formation of a structure composed of motor neurons, astrocytes and oligodendrocytes. The implication of LIF-related cytokines in the development of this nucleus came to light with the analysis of mice mutant for the receptor of these cytokines, LIFR beta, which exhibit a massive loss of facial branchiomotor (fbm) neurons at birth and a severe decrease in GFAP expression, a marker of astrocytes. To uncover the cellular mechanisms regulated by LIFR beta during facial nucleus development, we first analyzed its expression pattern in the hindbrain. lifr beta is first expressed at E11.5 in the hindbrain neuroepithelium. The receptor is absent during the migration of fbm post-mitotic neurons but is strongly expressed when fbm neurons have reached rhombomere 6 at E12.5, and its expression is maintained until E18.5. From the analysis of lifr beta mutant embryos, we established that LIFR beta is necessary for fbm neurons' identity determination. We also show that LIFR beta is implicated in astrocyte and oligodendrocyte differentiation, specifically within the facial nucleus.

GDNF acts through PEA3 to regulate cell body positioning and muscle innervation of specific motor neuron pools.

Target innervation by specific neuronal populations involves still incompletely understood interactions between central and peripheral factors. We show that glial cell line-derived neurotrophic factor (GDNF), initially characterized for its role as a survival factor, is present early in the plexus of the developing forelimb and later in two muscles: the cutaneus maximus and latissimus dorsi. In the absence of GDNF signaling, motor neurons that normally innervate these muscles are mispositioned within the spinal cord and muscle invasion by their axons is dramatically reduced. The ETS transcription factor PEA3 is normally expressed by these motor neurons and fails to be induced in most of them in GDNF signaling mutants. Thus, GDNF acts as a peripheral signal to induce PEA3 expression in specific motor neuron pools thereby regulating both cell body position and muscle innervation.