Genetic control of murine limb morphogenesis: relationships with human syndromes and evolutionary relevance

Cooperation of Hoxa5 and Pax1 genes during formation of the pectoral girdle

Hox and Pax transcription factors are master regulators of skeletal and organ morphogenesis. Some skeletal malformations encountered in Hoxa5 mutants are shared by the undulated (un) mice, which bear a point mutation in the Pax1 gene. To investigate whether Hoxa5 and Pax1 act in common pathways during skeletal development, we analyzed Hoxa5;un compound mutants. Our genetic studies show that Hoxa5 and Pax1 cooperate in the vertebral patterning of the cervicothoracic transition region and in acromion morphogenesis. The dynamics of expression of Hoxa5 and Pax1 in the pectoral girdle region suggest that both genes function in a complementary fashion during acromion formation. Whereas Pax1 is required for the recruitment of acromion precursor cells, Hoxa5 may provide regional cues essential for the correct formation of the acromion by ensuring Pax1 expression at the proper time and position during morphogenesis of the pectoral girdle. Hoxa5 also has a distinctive role in specifying the fate of perichondrial and chondrogenic cell lineages in a Sox9-dependent way.

Finger length and distal finger extent patterns in humans

The fingers in the adult human hand differ in length and in distal extent. The literature agrees that in the clear majority of males, the distal extent of the ring finger tends to be relatively greater (using the middle finger as standard) than the index finger. However, the results for females vary considerably, with some studies reporting that females show a similar pattern to that of males, while others suggest that the prevalence of a longer index finger is relatively or absolutely more common in females. We provide a review of the literature, and a set of data for both finger length and distal fingertip extent of the finger for a contemporary cohort of young adult females and males (n = 502). Finger length measures favor the ring finger of both sexes, with smaller between-finger differences for females than for males. However, while the distal fingertip extent favors the ring finger of both hands in males, in females the left hand shows no significant differences, and the right hand shows a small index finger advantage. Thus, the sexual dimorphism in finger measures is more strongly expressed in the distal extent of fingertips than in the length of fingers. The sex differences in distal fingertip extent derive from the index finger only, with a lesser distal extent of the index finger, relative to the middle finger, in males than in females.

Perspectives on the evolutionary origin of tetrapod limbs

The study of the origin and evolution of the tetrapod limb has benefited enormously from the confluence of molecular and paleontological data. In the last two decades, our knowledge of the basic molecular mechanisms that control limb development has grown exponentially, and developmental biologists now have the possibility of combining molecular data with many available descriptions of the fossil record of vertebrate fins and limbs. This synthesis of developmental and evolutionary biology has the potential to unveil the sequence of molecular changes that culminated in the adoption of the basic tetrapod limb plan.

Amphibian metamorphosis as a model for studying the developmental actions of thyroid hormone

The thyroid hormones L-thyroxine and triiodo-L-thyronine have profound effects on postembryonic development of most vertebrates. Analysis of their action in mammals is vitiated by the exposure of the developing foetus to a number of maternal factors which do not allow one to specifically define the role of thyroid hormone (TH) or that of other hormones and factors that modulate its action. Amphibian metamorphosis is obligatorily dependent on TH which can initiate all the diverse physiological manifestations of this postembryonic developmental process (morphogenesis, cell death, re-structuring, etc.) in free-living embryos and larvae of most anurans. This article will first describe the salient features of metamorphosis and its control by TH and other hormones. Emphasis will be laid on the key role played by TH receptor (TR), in particular the phenomenon of TR gene autoinduction, in initiating the developmental action of TH. Finally, it will be argued that the findings on the control of amphibian metamorphosis enhance our understanding of the regulation of postembryonic development by TH in other vertebrate species.

Amphibian metamorphosis as a model for studying the developmental actions of thyroid hormone

The thyroid hormones L-thyroxine and triiodo-L-thyronine have profound effects on postembryonic development of most vertebrates. Analysis of their action in mammals is vitiated by the exposure of the developing foetus to a number of maternal factors which do not allow one to specifically define the role of thyroid hormone (TH) or that of other hormones and factors that modulate its action. Amphibian metamorphosis is obligatorily dependent on TH which can initiate all the diverse physiological manifestations of this postembryonic developmental process (morphogenesis, cell death, re-structuring, etc.) in free-living embryos and larvae of most anurans. This article will first describe the salient features of metamorphosis and its control by TH and other hormones. Emphasis will be laid on the key role played by TH receptor (TR), in particular the phenomenon of TR gene autoinduction, in initiating the developmental action of TH. Finally, it will be argued that the findings on the control of amphibian metamorphosis enhance our understanding of the regulation of postembryonic development by TH in other vertebrate species.