Estimation of the number of hematopoietic precursor cells during fetal mouse development by covariance analysis

Differentiation of hematopoietic precursor cells results in the formation of clonally related descendent cells. Using the mosaic expression of beta-galactosidase in female mouse fetuses heterozygous for an X-linked lacZ transgene, we analyzed the clonal relationship of the hematopoietic progeny. The proportion of beta-galactosidase positive cells for different T- and B-lymphoid and myeloid cell populations was determined at different stages of fetal development. We found excellent correlations of the proportion of beta-galactosidase expressing cells for all hematopoietic lineages confirming that they share a common ancestry. Therefore, it was possible to estimate the number of common precursor cells (PC) based on binomial distribution and covariance analysis of pairs of different hematopoietic cell populations. Our results obtained from hematopoietic cells at 15.5 to 18.5 days of gestation indicated the presence of 15 to 18 lymphoid and 18 to 22 myeloid/lymphoid specific precursor cells. Statistical analysis of the precursor cell numbers showed a trend of increasing numbers that was highly significant. The precursor cell number was inversely related to maturity of the cell populations analyzed; ie, the lowest number of lymphoid and lymphoid/myeloid precursors was calculated when the most mature CD3+ T-cell population was used for comparison. Determination of PC numbers can therefore be used to assess the relative maturity and developmental potential of individual cell populations.