Sex Differences in Endogenous Retinoid Release in the Post-Embryonic Spinal Cord of the Western Mosquitofish, Gambusia affinis affinis

Abstract

Retinoic acid, a potent transcriptional activator, is believed to be an important factor in the regulation of vertebrate development (for review see Eichele, 1989; Gudas, 1994; Tabin, 1991; Boncinelli, et al., 1991; Kessel and Gruss, 1991a; 1991b; Kessel, 1992; Gudas, 1994). Retinaldehyde dehydrogenases catalyze the last step of retinoic acid synthesis and these enzymes are known to belong to a larger aldehyde dehydrogenases family (for review see Petersen and Lindahl, 1997). The distribution of endogenous retinaldehyde dehydrogenases in the developing animal sets up patterns of endogenous gradients of retinoic acid which modulate gene transcription and has been suggested to aid in establishing the developmental framework which organizes both the segmented body plan and the structure of individual organs (for review see Kessel and Gruss, 1991a; 1991b; Marsh-Armstrong, et al., 1995; 1994; Hyatt, et al., 1992; Watterson, et al., 1954; McCaffery, et al., 1991; 1992; McCaffery and Dräger, 1993; 1994; 1995; Dräger and McCaffery, 1995). This is clearly seen during the anteroposterior patterning of the trunk (Marsh-Armstrong, et al., 1994) in the Zebrafish, Danio rerio, in which an endogenous gradient of retinaldehyde dehydrogenase creates a matching gradient of retinoic acid along the anterior-to-posterior axis of the trunk, such as the pectoral, pelvic and anal fin. This occurs during the critical periods in embryogenesis when axial and appendicular structures are forming. Transcriptional regulation of the family of homeobox (Hox) genes, which are normally expressed in sequence along the length of the trunk (for review see Krumlauf, 1994; Krumlauf, et al., 1993; Kenyon, 1994; McGinnis and Krumlauf, 1992; Kessel and Gruss, 1991; Kessel, 1992), has been shown to be activated during development by retinoic acid in a sequential order, with 3′ end genes being activated more rapidly after exposure to retinoic acid, and 5′ end genes responding at progressively later times following retinoic acid exposure (for reviews see Krumlauf, 1994; Krumlauf, et al., 1993; Kenyon, 1994; McGinnis and Krumlauf, 1992; Kessel and Gruss, 1991; Kessel, 1992). Normal patterns of developmental gene expression, such as in the case of Hox genes, are altered in conditions of exogenous retinoic acid excess and deficiency (for review see Eichele, 1989; Gudas, 1994; Tabin, 1991; Boncinelli, et al., 1991; Kessel and Gruss, 1991a; 1991b; Kessel andGruss, 1991; Kessel, 1992; Langston and Gudas, 1994), resulting in “homeotic” transformations, which change the normal order of vertebrae (changing the phenotype of anterior vertebra to that of posterior vertebrae), or the neurons in the hindbrain (Manns and Fritzsch, 1992).