Authors:

Sharon G. Dayan

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About Paper:

The development of the vertebrate skeleton is controlled by several signaling cascades, including the TGF-B and BMP pathways, which are essential for bone growth, remodeling and craniofacial patterning [1]. These pathways play important roles in shaping phenotypic variation across fish and disruptions to them can produce dramatic morphological outcomes. Recent evidence from Lake Malawi cichlid fish has revealed how variations to TGF-8 signaling can impact craniofacial morphology, with smad7 identified as a candidate gene within a pleiotropic locus for oral and pharyngeal jaw shape that exhibits correlated expression between the two tissues [2]. We hypothesized that changes to TGF-8 signaling during early development would produce changes in craniofacial morphology consistent with known macroevolutionary trends in cichlids. To test this, we exposed a cichlid species, Labeotropheus fuelleborni, to stevia leaf extract, a compound known to alter TGF-8 signaling [3]. We reared juvenile (15 day) L. fuelleborni in stevia-infused water for 18 days, extracted RNA from body tissues, and utilized qPCR to assay TGF-B related gene expression. We observed a decrease in the inhibitory smad7 and an increase in the activating smad-2, -3, and -4, indicating an increase in TGF-B pathway expression, consistent with an over-activation of the TGF-f signaling pathway. Long term treatments, with L. fuelleborni exposed to stevia for 5 weeks, exhibited shorter and wider jaws, a pattern that mirrors macroevolutionary changes in cichlid jaw shape. These morphological shifts are consistent with known patterns of jaw divergence across Lake Malawi cichlids, where variation in TGF-f signaling has been linked to differences in both oral and pharyngeal jaw morphology. Our findings suggest that stevia impacts TGF-B signaling in L. fuellebori, potentially revealing a novel mechanism for modulating cichlid craniofacial morphology across the clade, and further implicating the TGF-f pathway as a key axis through which adaptive jaw shape diversity is generated.

Source:

DePaul University

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Co-authors:

Sharon G. Dayan