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Vertebrate limbs classically illustrate the morphological diversity of homologous structure. Bat limbs exemplify this, having strikingly divergent limbs: wings with asymmetrically elongated digit elements, supporting expansive membranes; and hindlimbs with short, symmetrical, free digits. An understanding of the genes, interactions and events that shape bat limbs, will inform conventional models of development. This dissertation characterised differential expression of Meis2, in the context of interdigital regression, and the 5'HoxD genes in the context of digit formation in developing bat autopods (CS15 - CS18). Meis2 is involved in limb proximodistal patterning, and has been shown to promote proliferation, and survival of cells in other developmental contexts. Meis2 had strong expression in the expanding bat forelimb interdigits, with lowered expression in mouse and bat hindlimb interdigits, and did not correspond with Hoxa13 expression, which was reduced in the forelimb. Autopod expression was independent of retinoic acid (RA) signalling, with genes involved in RA synthesis ( Rdh10 , Aldha2 ) , degradation ( Cyp26b1 ) and signalling (Rar β) expressed in bat limbs. Altered expression patterns of Aldha2 and Cyp26b1, indicate that this pathway may be modulated in the forelimb. Meis2 is suggested to play a role in interdigital tissue retention, enhancing cell proliferation and contributing to wing expansion. 5'HoxD genes (Hoxd10 - 13) are involved in limb patterning, digit formation and growth. Their modular autopod expression domains correspond to the bat skeletal element phenotype, with strong overexpression of Hoxd10 - 11 (and to a lesser extent Hoxd12) in the forelimb posterior elements (digits II - V), which are highly elongated, and a loss of expression of these genes in hindlimb digits. These genes were not expressed in a typical reverse collinear relationship, with absolute q PCR revealing highest expression of Hoxd10. While the coding protein sequence of these genes appeared highly conserved between bats and other mammals, several changes were found in the CsC region of the digit enhancer Prox, some of which were associated with alterations in transcription binding sites. These findings indicate that Hoxd10 - 12 expressions contribute to the altered skeletal element morphologies of bat forelimbs and hindlimbs. This study makes a valuable contribution to the growing body of work that explores bat limb development and the evolutionary adaptation s of these unique structures.

This study reports the first characterisation of the embryonic bat limb transcriptome, allowing the identification of novel candidate genes that were differentially expressed between the bat hand and foot plate. These genes may have played important roles in the evolution of the bat wing and hindlimb. The reproduction and development of an African bat species, Miniopterus natalensis, was characterised and three maternal features (mass, belly size and plasma progesterone levels) examined as potential predictors of embryonic stages of development. Belly palpitation was found to be a useful field method to distinguish between non-pregnancy, early development or late development in female bats. A microarray analysis between the hand and foot plates of CS 16 and CS 17 bat embryos, and the hand plates of E 13.5 mouse embryos, revealed high correlation between the transcriptomes of the bat autopods and the mouse hand plate (r > 0.88) and among all the bat autopods (r > 0.98). However, ten genes were found to be differentially expressed in both the CS 16 and the CS 17 bat hand plate as compared to the mouse hand plate while only three genes were identified as being significantly differentially expressed between bat foot plates and mouse hand plates. A comparison between the bat hand and foot plates identified fifteen genes that were differentially expressed at the stage CS 17 stage and six at the stage CS 16. Closer examination of gene families involved in limb development revealed novel expression of genes in the retinoic acid (RA) pathway, and the Hoxd family. This included the apparent co- regulation of the 5' Hoxd genes (Hoxd10, 11, 12 and 13). Of the genes characterised in bat limb development (Hoxd13, Bmp2, Fgf8 and Prrxl), higher mRNA transcript levels in the CS 17 bat hand plate relative to the mouse hand plate was found for Hoxd13 (FC = 2.6) and Prrxl (FC = 1.8). These differences were also found in a comparison to the CS 17 bat foot plate (Hoxd13: FC = 1.4; Prrxl: FC = 1.4). A potentially novel transcript of Meis2, a gene important in specifYing the proximal-distal (P-D) axis of the limb, was noted for its high fold changes in the bat hand plate as compared the foot plate (CSI7: FC = 7.0; CSI6: FC = 2.2) and the mouse hand plate (FC = 13.1).